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Solving a sweet problem for renewable biofuels and chemicals

June 30, 2017

ASU scientists harness the trial-and-error power of evolution to coax nature into revealing answer to energy challenge

Whether or not society shakes its addiction to oil and gasoline will depend on a number of profound environmental, geopolitical and societal factors.

But with current oil prices hovering around $50 dollars a barrel, it won’t likely be anytime soon.

Despite several major national research initiatives, no one has been able to come up with the breakthrough renewable biofuel technology that would lead to a cheaper alternative to gasoline. 

That research challenge led ASU scientists Reed Cartwright and Xuan Wang to enter the fray, teaming up to try to break through the innovation bottleneck for the renewable bioproduction of fuels and chemicals.

“My lab has been very interested in converting biomass such as agricultural wastes and even carbon dioxide into useful and renewable bio-based products,” said Wang
(pictured above, right), an assistant professor in the School of Life Sciences. “As a microbiologist, I’m interested in manipulating microbes as biocatalysts to do a better job.”

To do so, they’ve looked into a new approach: harnessing the trial-and-error power of evolution to coax nature into revealing the answer.

By growing bacteria over generations under specially controlled conditions in fermentation tanks, they have test-tube-evolved bacteria to better ferment sugars derived from biomass — a rich, potential renewable-energy source for the production of biofuels and chemicals. Their results appeared recently in the online edition of PNAS.

The research team includes postdoctoral scholar Christian Sievert, Lizbeth Nieves, Larry Panyon, Taylor Loeffler and Chandler Morris, and was led by Cartwright and Wang, in a collaboration between the ASU’s School of Life Sciences and the Biodesign Institute.

A sweet problem

The appeal of plants is ideal. Just add a little carbon dioxide, water and plentiful sunshine, and presto! Society has a rich new source of renewable carbons to use.  

Corn ethanol (using starch from corn for alcohol production primarily in the U.S.) has been one major biofuel avenue, and sugarcane another alternative (abundant in Brazil) — but there is a big drawback. Turning the sugar-rich kernels of corn or sugarcane into ethanol competes with the food supply.

So scientists over the past few decades have migrated to research on conversion of non-food-based plant materials into biofuels and chemicals. These so-called lignocellulosic biomasses, like tall switchgrasses and the inedible parts of corn and sugarcane (stovers, husks, bagasses, etc.) are rich in xylose, a five-carbon, energy-rich sugar relative of glucose.

Lignocellulosic biomass has an abundance of glucose and xylose, but industrial E. coli strains can’t use xylose because when glucose is available, it turns off the use of xylose. And so, to date, it has been an inefficient and costly to fully harvest and convert the xylose to biofuels. 

Benchtop evolution

Wang and Cartwright wanted to squeeze out more energy from xylose sugars. To do so, they challenged E. coli bacteria that could thrive comfortably on glucose — and switch out the growth medium broth to grow solely on xylose.

The bacteria would be forced to adapt to the new food supply or lose the growth competition.

They started with a single colony of bacteria that were genetically identical and ran three separate evolution experiments with xylose. At first, the bacteria grew very slowly. But remarkable, in no more than 150 generations, the bacteria adapted and, eventually, learned to thrive in the xylose broth. 

Next, they isolated the DNA from the bacteria and used next-generation DNA sequencing technology to examine the changes within the bacteria genomes. When they read out the DNA data, they could identify the telltale signs of evolution in action, mutations.

Nature finds a way

The bacteria, when challenged, randomly mutated their DNA until it could adapt to the new conditions. They held on to the fittest mutations over generations until they became fixed beneficial mutations.

And in each case, when challenged with xylose, the bacteria could grow well. Their next task was to find out what these beneficial mutations were and how did they work. To grow better on xylose, the three bacterial E. coli lines had “discovered” a different set of mutations to the same genes. The single mutations the research team identified all could enhance xylose fermentation by changing bacterial sugar metabolism.

“This suggests that there are potentially multiple evolutionary solutions for the same problem, and a bacterium’s genetic background may predetermine its evolutionary trajectories,” said Cartwright, a researcher at ASU’s Biodesign Institute and assistant professor in the School of Life Sciences.  

The most interesting mutation happened in a regulatory protein called XylR whose normal function is to control xylose utilization. Just two amino acid switches in the XylR could enhance xylose utilization and release the glucose repression, even in the non-mutated original hosts.

Through some clever genetic tricks, when the XlyR mutant was placed back in a normal “wild-type” strain or an industrial E. coli biocatalyst, it could also now grow on xylose and glucose, vastly improving the yield. Wang’s team saw up to a 50 percent increase in the product after four days of fermentation. 

Together, Wang and Cartwright’s invention has now significantly boosted the potential of industrial E. coli to be used for biofuel production from lignocellulosic materials. In addition, they could use this same genetic approach for other E. coli strains for different products.

Arizona Technology Enterprises (AzTE) is filing a non-provisional patent for their discovery. Wang hopes they can partner with industry to scale up their technology and see if this invention will increase economic viability for bioproduction.  

“With these new results, I believe we’ve solved one big, persistent bottleneck in this field,” Wang said. 

Top photo: ASU undergraduate Eric Taylor (left) and Xuan Wang demonstrate the fermentation tanks used in the benchtop evolution experiments.​

Joe Caspermeyer

Manager (natural sciences) , Media Relations & Strategic Communications

480-727-4858

ASU professor leads gender workshop for STEM careers in Pakistan

U.S.-Pakistan Centers for Advanced Studies in Energy makes headway in gender quality


May 22, 2017

The U.S.-Pakistan Centers for Advanced Studies in Energy (USPCAS-E) held a workshop in Islamabad, Pakistan this spring with the hopes of improving gender equity for women in science, technology, engineering and math fields.

The three-day workshop was helmed by Professor Chad Haines of Arizona State University, who specializes in cultural anthropology and topics related to the contemporary Muslim world. The prominence of women in STEM fields from Pakistan differs greatly depending on the region according to Haines. In the Punjab region for example, 20 to 30 percent of STEM students are women. In the Khyber Pakhtunkhwa region, the percentage of women is actually much lower. Participants of the ASU/USPCAS-E workshop on gender. Photographer: Hassan Zulfiqar/USPCAS-E Participants of the ASU/USPCAS-E workshop on gender. Photo by Hassan Zulfiqar/USPCAS-E Download Full Image

Haines summarized that the challenge in the region, “is creating a foothold where women are encouraged and supported and based on that, there is much greater potential for increasing the number of Pakistani women in the STEM fields.”

The workshop is part of a greater effort by USPCAS-E, which is a project funded by USAID as part of a partnership between Arizona State University and two leading Pakistani universities: the National University of Sciences and Technology (NUST) and the University of Engineering and Technology (UET) Peshawar. The goal is to focus on applied research relevant to Pakistan’s energy needs and help produce skilled graduates in the field of energy. Fostering student and faculty exchanges are part of a greater goal, which also includes an emphasis in gender equality.

The workshop attracted a variety of participants including students, educational administrators, professors, researchers as well as professionals from the engineering field.

Muhammad Asad, a professional engineer who attended the workshop said that the subject of gender equality was eye-opening for him. “I [had] never heard about this type of topic being discussed on this kind of platform before.” Asad had high hopes about the workshop saying, “it all starts from self-development you know. If you learn something then you practice it yourself.” The workshop has the potential to ripple beyond its original audience. Asad has plans to disseminate what he has learned throughout his social circles.

There was a mix of both men and women attending the event, some of whom were seeking role models and others, inspiration. H. Masooma Naseer Cheema, a scientist and assistant professor said she attended to, “revitalize my passion and keep my spirit high by knowing that I am not alone in the journey of becoming a successful professional female.” Speaking from experience she said, “the life of a professional career women is not an easy task.”

Following the workshop, another attendee, Anaiz Gul Fareed, who is a graduate student at NUST hoped to spread, “awareness to different localities and [various] under-developed areas of my country regarding girls education.”

Ishtiaq Hussain, who is self-described as being from a very conservative family expressed that, “Before attending the workshop I was not really in favor of females getting an equal opportunity everywhere, but now I have learned how to help females and provide them with an equal opportunity to become a successful.”

Cultural anthropologist Professor Chad Haines of Arizona State University speaks on a panel about gender equity to an audience in Pakistan. Photographer: Hassan Zulfiqar/USPCAS-E

Content is king ... and queen

The format of the workshop was less of a lecture, and more of an open exchange of ideas.

Cheema praised the event saying that, “most of the gender equity-related workshops usually address women. But [the] good thing about this workshop is that it addressed both genders.”

Participants weighed and analyzed the difference between, equality, equity and justice. “I would like to get justice rather than equity and equality,” Cheema said.

Anaiz Gul Fareed reflected on several examples of gender inequity, citing, “that there are several offices in Pakistan where there are no facilities for women restrooms.” He also learned that, “more than 50 percent of girls who opt for medical sciences,” may do so, “just because they can get a well-settled boy to marry.”

“While attending this session, I decided to help my three daughters to grow without limiting them,” Fareed said. “I promised myself that I would help them to achieve whatever they want to.”

The workshop hoped to reach individuals because it is the everyday administrators, faculty members, professional and students who become empowered to speak up that possess the potential to foster a culture of gender equity and encourage women in the STEM fields.

Gender issues in Pakistan are also addressed by the project through a scholar exchange program in which ASU which has had an exponential growth of female participants.

To date, this is the fifth workshop that USPCAS-E and ASU has held in Pakistan on various topics related to the project, including green building practices and photovoltaics to name a few.

USPCAS-E will continue to deliver workshops in Pakistan through 2019.

Erika Gronek

Communications Specialist, Ira A. Fulton Schools of Engineering

ASU Fulton Schools graduates 17 more Grand Challenge Scholars to tackle global challenges


May 15, 2017

Engineers strive to better the world through technology and new ideas. However, engineering alone can’t solve the world’s problems.

High-achieving students in Arizona State University’s Ira A. Fulton Schools of Engineering go above and beyond the typical engineering curriculum in the Grand Challenge Scholars Program (GCSP), as they learn to be collaborative, transdisciplinary, global problem solvers. 13 of the 17 Spring 2017 Grand Challenge Scholars pose for a group photo at the Grand Challenge Scholars Program Graduation Reception. Thirteen of the 17 Grand Challenge Scholars graduating in spring 2017 celebrated at the Grand Challenge Scholars Program Graduation Reception on April 19. This semester's group is the largest cohort of graduating GCSP students. Photographer: Marco-Alexis Chaira/ASU Download Full Image

This spring, the GCSP program graduated 17 students — the largest cohort yet. These graduates will be added to the official Grand Challenge Scholars Registry.

“I am extremely proud of all the students’ accomplishments, and the people they have become,” says Amy Trowbridge, lecturer and director of the ASU GCSP. “Our graduates this year have published their research in journal articles, started entrepreneurial ventures, immersed themselves in new cultures through studying or implementing projects abroad, and have completed service learning projects that have impacted the community, both locally and globally.”

Students prepare to solve global challenges

The National Academy of Engineering has designated 14 Grand Challenges facing society over the next century.

  • advance personalized learning
  • make solar energy economical
  • enhance virtual reality
  • reverse-engineer the brain
  • engineer better medicines
  • advance health informatics
  • restore and improve urban infrastructure
  • secure cyberspace
  • provide access to clean water
  • provide energy from fusion
  • prevent nuclear terror
  • manage the nitrogen cycle
  • develop carbon sequestration methods
  • engineer the tools of scientific discovery

GCSP scholars choose one of these grand challenge or a broader grand challenge theme — education, energy, health, security or sustainability — and complete five program requirements around that theme.

Students engage in research relating to their selected grand challenge, explore interdisciplinary coursework, gain an international perspective, engage in entrepreneurship, and give back to the community through service learning.

After completing these program requirements, students are designated Grand Challenge Scholars by ASU and the National Academy of Engineering, and added to the official Grand Challenge Scholars Registry.

A growing program

Arizona State University’s Grand Challenge Scholars Program began in 2011 as the largest participating school in the United States.

The program started with about 60 students admitted, and has grown to more than 400 scholars at all levels.

These scholars are a diverse group, with 31 percent female students and 23 percent underrepresented minorities, Trowbridge says.

More than half of GCSP scholars are also in Barrett, the Honors College, and others are Entrepreneurship + Innovation Fellows, both of which are highly ambitious programs that offer a well-rounded experience.

Since the Grand Challenge Scholars Program produced its first graduate in 2013, graduation rates have grown significantly.

  • 1 graduate in 2013
  • 3 graduates in 2015
  • 11 graduates in 2016
  • 17 graduates in the spring 2017 semester

Trowbridge believes this growth is due to a variety of factors on the program side and student side.

Coordinator Senior for Undergraduate Student Engagement Jade Silva, recent biomedical engineering graduate Mariama Salifu and Lecturer and Director of the ASU Grand Challenge Scholars Program Amy Trowbridge. Photographer: Marco-Alexis Chaira/ASU

Left to right: Jade Silva, coordinator senior for Undergraduate Student Engagement, recent biomedical engineering graduate Mariama Salifu, and Amy Trowbridge, lecturer and director of the ASU Grand Challenge Scholars Program. Photo by Marco-Alexis Chaira/ASU

“Over the past few years we have implemented several efforts to provide opportunities and support for students to enhance their experience and success from their first day in the program,” Trowbridge said, adding that “students have worked hard to provide additional support and opportunities for each other through the affiliated student organization, the Grand Challenge Scholars Alliance.”

Jade Silva, coordinator senior for undergraduate student engagement, also credits an increase in dedicated staff and resources to help scholars understand the program’s requirements and how to progress without significantly increasing their course load.

“The focus on adding more staff and faculty support to the program, as well as the summer institute, made it something that was a hands-on learning experience for incoming first-year students into the program,” Silva said.

Support continues for students through checklists, required meetings and degree audits that have a positive effect on keeping students engaged and progressing through program requirements.

“The support from Jade Silva and Amy Trowbridge is overwhelming,” said Kaleia Kramer, a biomedical engineering recent graduate. “They do everything they can to help you succeed, so there is less concern for the students. We can just focus on doing well in the classes.”

A dedicated community of scholars

When introduced to the program, students are excited to see the exceptional opportunities GCSP presents.

“I saw that it was a nationally recognized program … and I also liked the emphasis on things such as research and service learning,” says chemical engineering spring 2017 graduate Lyle Bliss.

Students looking for a well-rounded education find that GCSP requirements help them meet their academic goals.

“I decided to apply because I believed it was an amazing program that would help me customize my college experience,” said Mariama Salifu, a recent biomedical engineering graduate. “Having [the GCSP requirements] gave me discipline to do extracurricular activities like research.”

The program also aligns well with activities students are often already involved in, including Engineering Projects in Community Service (EPICS), the Fulton Undergraduate Research Initiatives (FURI) and others.

“The requirements list seemed like the perfect recipe for engineers to be prepared after graduating,” Kramer saod. “In addition, most of the requirements were things I was already looking to do — I was already in a research lab, enrolled in EPICS and was very interested in entrepreneurship.”

As students have these positive experiences, word of mouth helps get their peers involved and has led to program growth, Silva said.

A connection between GCSP students in the program is also a key factor to their success, Trowbridge said.

“The students’ connection to each other and the community they built was one of the biggest factors for their success and engagement in the program,” Trowbridge said. “Several of the students have mentioned that staying connected with our ASU GCSP community kept them motivated to succeed in the program.”

A once-in-a-lifetime experience

It’s a challenging program, but one that ultimately pays off, Kramer said.

“It wasn’t until my junior year that the rewards of the program started to come back to me,” Kramer said. “As a freshman and a sophomore it seemed like I was just taking extra classes and I could see why some students were dropping out.”

Staying involved in the program provided her with many unique opportunities, including an invitation to the first annual White House BRAIN Conference in 2014, followed by a trip to the Global Grand Challenges Summit in Beijing, China, in 2015.

Scholars graduating this semester have studied global issues, and some even traveled the world, with studies and ventures taking them to Aruba, the United Kingdom, Ghana, Kenya, Israel, India and China.

Photo of Raquel Camarena and Tirupalavanam Ganesh.

Raquel Camarena, industrial engineering recent graduate, and Tirupalavanam Ganesh, GCSP mentor, associate research professor and assistant dean of engineering education. Photo by Marco-Alexis Chaira/ASU

Students also gained new perspectives on engineering issues through courses across the university in related subjects such as biology and sustainability, but also the seemingly unrelated topics of anthropology, sociology, urban planning, cultural geography, political science and management.

“The experiences that students have as part of GCSP have helped them to better understand how and why they as engineers need to work with people from other disciplines to develop solutions to the interdisciplinary, global problems we face,” Trowbridge says.

These experiences also give them purpose.

“Students can find meaning — social and personal relevance — in their chosen profession, and know that they can impact the world in significant ways, improving life locally and globally through their work while pursuing their undergraduate degree and beyond,” said Tirupalavanam Ganesh, GCSP mentor, associate research professor and assistant dean of engineering education.

Kramer and Bliss have obtained internships through the connections they made while completing the program requirements, and feel confident that their experience has prepared them for industry jobs and grad school, respectively.

Finding other callings through GCSP experiences

Though hundreds of students are involved in GCSP, few complete all program requirements, but Silva says this is not an entirely negative outcome.

“When students leave the program, it’s not a loss,” Silva said. “It means that the program did what we wanted it to do — to get students to start to explore, get that experience and find who they want to be as problem solvers.”

In completing research, entrepreneurship, service learning and other requirements, students might find passion in one of the five areas of the GCSP requirements, like an Engineering Projects in Community Service project, a startup, research in a specific faculty member’s lab, or leadership in a student organization.

No matter where they end up, they’re prepared to help the world.

“These students really are the future of engineering and technology, and they are committed to solving some of the world’s toughest problems,” Silva said. “It’s really breaking down this idea that engineers are just technical people, that they are just doing the behind-the-scenes work. These students really understand the importance of what they’re doing, how it impacts society and their role in society. I’m excited to see how they impact the world for the better.”

Monique Clement

Communications specialist, Ira A. Fulton Schools of Engineering

480-727-1958

Postcards from the ledge

Hoover Dam excursion for Pakistani scholars bridges knowledge, culture


May 4, 2017

A group of 27 Pakistani engineering scholars from the U.S.-Pakistan Centers for Advanced Energy, better known as USPCAS-E, set off on an adventure over spring break, learning what nature can engineer, what people can engineer and the power their imagination has to inspire innovation.

An $18 million United States Agency for International Development grant supports the project with Arizona State University as the hub for the energy component of the project in partnership with the National University of Science and Technology — Islamabad (NUST), the University of Engineering and Technology in Peshawar and Oregon State University. “Big dams in Pakistan are normally earth and rock fill dams, so there is a need to build concrete arc dams like Hoover Dam in Pakistan that are more impressive, efficient and modern,“  says Muhammad Ahsan Amjed, NUST. Photo courtesy of Muhammad Ahsan Amje “Big dams in Pakistan are normally earth and rock fill dams, so there is a need to build concrete arc dams like Hoover Dam in Pakistan that are more impressive, efficient and modern,“ say Muhammad Ahsan Amjed, National University of Science and Technology. Photo courtesy of Muhammad Ahsan Amjed Download Full Image

The scholars are part of the third cohort to visit the United States in order to study renewable energy at ASU’s Ira A. Fulton Schools of Engineering as part of a larger effort to boost development of solutions for Pakistan’s growing energy needs. Spring break offered a respite from their classes and lab work, and provided a chance to see engineering in action.

The scholars kicked off their journey by visiting one of nature’s greatest engineering wonders, the Grand Canyon. The canyon stood as a compelling example of the power found in nature, as seen by the river carving away at the landscape for millennia. The challenge for the scholars was to learn from nature and learn how to harness that energy.

Their next stop at Hoover Dam illustrated just that. The scholars saw first hand how the Colorado River was used as a source of renewable hydroelectric power through ingenuous civil engineering.

USPCAS-E Scholars, Left to right: Farah Akram, Anam Zahra, Maham Akhlaq, Atoofa Zainab, Photographer: Erika Gronek/ASU

“The sheer brilliance that the engineers displayed in [their] era with such a megastructure was a rarity, [and] is a sight to behold. It solved the water distribution problems for seven different states,” said Haider Saif Agha from NUST.

Learning about this pinnacle of clean energy was key for the scholars because many of them are studying photovoltaic, wind and hydroelectric energy options. The USPCAS-E project set out to explore renewable energy as a means for resolving the energy crisis happening in Pakistan today, leaving the country with rolling blackouts that last 6–16 hours a day.

The dam was created for the purposes of flood control, irrigation and power production, all of which are applicable to Pakistan’s needs.

“I see a comparison with Pakistan’s Kalabagh Dam,” said Asfand Yar Ali, of the University of Engineering and Technology, Peshawar. Kalabagh Dam is proposed dam that could help Pakistan with flood control. “We are facing minor and major floods every year in [the] monsoon [season]. Similarly, the dam will help Pakistan rejuvenate its agriculture and overcome [the] energy crisis.“

Hoover Dam was an example of what could be implemented back home for the scholars.

“I learned that we can solve all of our country’s energy problems by just mixing innovation and engineering in the right proportions,” said Usman Salahuddin of NUST.

To shake things up, the scholars next visited the California Science Center. Atoofa Zainab of NUST had a personal favorite there – the earthquake simulator.

“I learned about the how certain buildings are made in case of an earthquake. The lesson that I learned is that Pakistan is in dire need of these types of services and technologies.”

Inspiring the heart and the exchange of culture

Inside Hoover Dam. Photo credit: Usama Khalid, NUST/ASU.

Though engineering is the primary point of USPCAS-E, other aspects of the initiative like promoting gender equality and engaging in cultural exchange are key aspects as well. The scholars expressed heartfelt thanks to be a part of a program that educates not just their inner engineer, but also cements their role as a global citizen.

“I have honestly no words to define my experience I had on spring break. It was both fun and a learning experience,” said Farah Akram of NUST. “The places we visited showed us a new face of the world. The views of the Grand Canyon, [the] innovative construction of Hoover Dam, fun and virtual reality-based rides of Universal Studios, learning at the California Science Center and [having a] playful time in Santa Monica gave us the most beautiful time of our lives.”

“Something that really impacted my heart was the celebration of diversity in America. America celebrates its diversity, be it in L.A., Tempe, Las Vegas or any other city. I was impacted by views on tolerance, freedom of speech, action,” reflected Haider Saif Agha of NUST.

Muhammad Ahsan Amjed of NUST ruminated that, “if you really want to understand the culture and people of any particular area, you will have to travel across that region in order to better understand their traditions, their peculiarities, cultural idiosyncrasies [and] subtle differences in their way of living. Such excursions help us renew our perspective about our research, our lives and our goals.”

The cultural exchange component of the program provides unlimited opportunity for visitors and Americans to engage with each other, allows visitors to find their place in the global community, breaks down prejudices and misunderstandings, and in the long-term expands and strengthens relationships between the two countries.

Erika Gronek

Communications Specialist, Ira A. Fulton Schools of Engineering

ASU engineer looks to improve next-gen materials for solar cells


April 25, 2017

New findings by an Arizona State University engineer outline new advances in solar cell technology and point to the incredible potential of the material used to fabricate the cell — gallium nitride.

A research paper published April 17 in Applied Physics Letters details electrical engineering Assistant Professor Yuji Zhao’s efforts to use gallium nitride to create a high-performance solar cell capable of operating under extremely high temperatures. Electrical engineering Assistant Professor Yuji Zhao stands in his Metal-Organic Chemical Vapor Deposition lab on the Tempe campus, where he works with gallium nitride, a compound with unique properties. Zhao's research is focused on exploring gallium nitride's use in optoelectronics and high-power and high-frequency devices. Photo by Pete Zrioka/ASU Download Full Image

Gallium nitride is a unique compound, the properties of which make it an excellent candidate for use in optoelectronics and high-power and high-frequency devices.

“This material is remarkable and has such high potential,” Zhao said.

Zhao notes that some have called gallium nitride the next silicon — the ubiquitous material that serves as an integral component of many of our electronics, from computer chips and solar cells to transistors and integrated circuits. Gallium nitride could prove to be superior to silicon, and Zhao’s work is paving the way toward faster, more efficient and higher-powered devices of all kinds.

Zhao first began working with the material under pioneering researcher Shuji Nakamura of the University of California, Santa Barbara. Nakamura was awarded the Nobel Prize in Physics in 2014 for developing efficient blue-light-emitting diodes, which has enabled bright and energy-saving white-light LEDs.

While working toward his doctorate, Zhao focused on employing gallium nitride for use in LEDs and lasers. Now he’s taken the material far beyond optoelectronics, expanding its use for solar panels, power systems and more. His exploration of the material’s myriad uses has earned him support from both NASA and the U.S. Department of Defense.

In 2015, Zhao was awarded a prestigious Early Career Faculty Space Tech Research Grant from NASA, a first for Fulton Schools faculty. The award supported the focus of his Applied Physics paper to create high-temperature resistant solar cells.

“They have high hopes for this project. They seem to believe this is one of the most promising methods to achieve their goals,” Zhao said.

Currently, Zhao is prototyping the solar panels, and will begin thermal testing soon.

“It’s not a question of whether or not the panels will work under high temperatures, but of how efficiently they will perform,” Zhao said.

More recently, he received a $300,000 award from the DOD’s Defense Threat Reduction Agency, which supports basic research to counter weapons of mass destruction. Zhao’s work with the DTRA is focused on using aluminum nitride to create transistors that can withstand high voltage and resist radiation damage.

To test this, he and his team will construct a Schottky Diode — a basic two-terminal electric component — and place it in a radioactive environment, subjecting it to different types of radiation in varying doses and rates of exposure. This radioactive stress test will eventually cause degradation in performance in the diode. That’s when Zhao will turn to materials studies to determine how to improve the material’s resistance and performance.

The applications are far reaching, such as for more robust power electronics and communications systems, but the DTRA is primarily interested in military devices that would remain operational following a radiation event, Zhao said.

Zhao credits his success in attracting funding to refine materials and explore their uses to the work being done in his cutting-edge Metal-Organic Chemical Vapor Deposition lab on the Tempe campus.

“One of the key reasons I was awarded these grants was first my background with this work, but also the capability of the MOCVD lab,” Zhao said. “The equipment we use is industry standard, not different from what you’d find in a major company.”

The lab required an estimated investment of $800,000 to set up and became fully operational in fall 2016.

He envisions the lab as a truly interdisciplinary space, and not only because his research draws on the expertise of physicists, materials scientists and device designers. Zhao wants the MOCVD lab to be an unparalleled resource for all of the Fulton Schools.

His ultimate goal mirrors the Nobel Prize description: developing science and tech for the betterment of humanity. He’s chosen refining and improving next-generation materials, such as gallium nitride, as his avenue to do so.

“The idea is to benefit as much of ASU as possible, which will hopefully extend outside of the university as well,” Zhao said.

Pete Zrioka

Communications specialist, Office of Knowledge Enterprise Development

480-727-5631

 
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Federal officials tour ASU's photovoltaics lab, the nation's largest

ASU boasts nation's largest photovoltaic research facility, key to solar power.
ASU expert says a trillion dollars will be invested into solar in next 20 years.
April 24, 2017

Solar research facility on Tempe campus poised for big developments

Federal representatives are visiting Arizona State University’s powerhouse photovoltaics lab this week to review progress made in research on the energy of the future.

ASU’s Quantum Energy and Sustainable Solar Technologies Engineering Research Center is the largest photovoltaic research facility in the country, and the only one funded by the National Science Foundation and the Department of Energy.

In the past year, more solar has been installed than any other source of electricity. Photovoltaic installations were up 95 percent in 2016. There are more jobs in solar than exist in oil or gas extraction. It’s a power source supported by all sides of the political spectrum.

Society’s advancement is tied to the amount of energy it can harness, center director Christiana Honsberg said. Right now, compared with automotive technology, solar cells are at a Ford Model T level.

Solar is at a tipping point, Honsberg said. In the next 20 years, about a trillion dollars will be invested.

“In a lot of ways, the goal is to define a path that helps that trillion-dollar industry become more sustainable and addresses a lot of the critical issues,” she said.

The center identifies technical barriers to sustained improvement — high efficiency, scalability and sustainability — and tackles them by breaking down research barriers.

“Our central defining feature is that you can continue to improve both the cost of solar at the same time you improve its performance,” Honsberg said. “You continue to get higher efficiency and lower cost simultaneously. That’s a little bit hard to do. As cars improve, they get more expensive. … Semiconductor technologies get better and cheaper, but most things don’t get better and cheaper.”

QESST Lab

 ASU Quantum Energy and Sustainable Solar Technologies Engineering researchers deposit one of many layers while building a solar cell. Photo by Jessica Hochreiter/ASU

 ASU’s center opened in 2010 and has been ramping up every year, adding facilities and faculty. It started with two faculty members and now has seven.

It holds several world records.

“Some of them are true world records, and some are voltage records,” Honsberg said. “The term ‘world record’ is very precisely defined in solar. … The fact that we hold the voltage record in every commercially relevant material is significant in that our physics and ideas are better than anything else out there.”

Engineering Research Centers are the largest awards bestowed by the National Science Foundation. At any given time, there are only 20 ERCs operating in the country. It’s a prestigious and rare award. Only one-quarter of 1 percent of applicants to the program win funding. It’s a 10-year award, given only after five stringent reviews.

ASU has two of them.

“ASU has really ramped up in the ERCs,” Honsberg said. “There aren’t a whole lot of ERCs, given the very, very broad mission that NSF funds in.”

This week’s visit by a 15-member team is one of three funding reviews during the 10-year period of the award. As well as learning what taxpayer dollars are discovering, they’ll get a look inside how ASU operates.

“We are absolutely embedded into ASU’s mission,” Honsberg said. “Every single aspect of what we do fits in directly. One of the key things we want to do is change the standard university picture of people just sitting in a lab producing papers in obscure journals to actually being able to tackle larger problems and make a larger impact.

“If you’re going to do that, the single-faculty, single-lab model is not the right model. … We want to not only make an impact on a big problem, but we’re also working to develop how you optimally combine many different universities, different (principal investigators), how you integrate education in.” 

Top photo: Solar cells — such as this one being examined by researchers at ASU’s Quantum Energy and Sustainable Solar Technologies Engineering Research Center — are poised to become more efficient and cheaper thanks to an influx of investments. Photo by Jessica Hochreiter/ASU

Scott Seckel

Reporter , ASU Now

480-727-4502

Young engineers envision an energy-independent Pakistan


April 10, 2017

Improving the energy grid in Pakistan is, without exception, the priority for a cohort of Pakistani graduate scholars studying engineering at Arizona State University this semester.

Participants in the U.S.–Pakistan Centers for Advanced Studies In Energy program, the students recently demonstrated renewable energy concepts during ASU’s Night of the Open Door — an event during which Phoenix-area residents visit campus, meet faculty and students, and explore research projects.  Above: Hira Rehman (in pink) and Asma Shamim (in gold) demonstrate the power of photovoltaics with members of the Tempe community during Night of the Open Door. Photographer Erika Gronek/ASU Above: Hira Rehman (in pink) and Asma Shamim (in gold) demonstrate the power of photovoltaics with members of the Tempe community during Night of the Open Door. Participants in the U.S.–Pakistan Centers for Advanced Studies In Energy program, the students recently demonstrated renewable energy concepts during ASU’s Night of the Open Door – an event during which Phoenix-area residents visit campus, meet faculty and students, and explore research projects. Photo by: Erika Gronek/ASU Download Full Image

Toy solar car races at the USPCAS-E exhibit attracted many young guests, giving the engineering students an opportunity to explain the importance of developing renewable sources of power. They also handed out LED light-up fans that, when they spin, spell out, “Renewable Energy: I’m a big fan.”

USPCAS-E is a partnership between ASU and two leading Pakistani universities: the National University of Science and Technology Islamabad and the University of Engineering and Technology in Peshawar. Funded through the U.S. Agency for International Development, the program is designed to find innovative solutions to Pakistan’s energy challenges. The group of students, comprised of 18 men and 11 women, represents the third cohort to spend a semester at ASU before returning to Pakistan to complete their master's degrees.

Ussama Khalid Barki (left) and Usman Salahuddin (right) explain how photovoltaics could change the energy situation in their home country at Night of the Open Door – Polytechnic. Photographer Erika Gronek/ASU

Ussama Khalid Barki (left) and Usman Salahuddin (right) explain how photovoltaics could change the energy situation in their home country at Night of the Open Door on the Polytechnic campus. Photo by Erika Gronek/ASU

Different backgrounds lead to diverse solutions to common goal

A NUST grad with a bachelor’s degree in telecommunications engineering, Anam Zahara from Southern Punjab is now working on a master’s degree in energy policy, with a focus on electrical engineering, through the program.

“We have many rolling blackouts in my area of the country,” she explained. Her vision is to integrate her telecommunications and electrical engineering education so she can “be a part of the process that improves Pakistan’s energy infrastructure.”

Education is a priority in Zahara’s family – both parents are teachers, two sisters are medical doctors and another has a master’s degree in agriculture. 

“One thing I’ve learned here is that time is money,” she said. “It’s important to be punctual for class.”

For Usman Salahuddin from Karachi, the decision to pursue an advanced degree in energy systems was born of frustration. With a bachelor’s degree in chemical engineering from NUST, Salahuddin found himself literally powerless on the job almost daily in the fertilizer industry.

“There was not enough gas to feed the furnace, so we’d have to shut down the factory,” he explained. “It taught me that we cannot rely on fossil fuels. We must develop renewable technologies that can be safely implemented for industry.” 

His attraction to the USPCAS-E program was heightened by the opportunity to focus on entrepreneurship. “This program not only makes us researchers, it also emphasizes becoming entrepreneurs,” Salahuddin said. “I believe small start-up companies will contribute significantly to solving my country’s energy problems.”

“Physics is about making theories,” said Ussama Khalid Barki, who holds a physics degree from NUST. “Engineering is about execution.” Noting that his country is struggling, Barki said it’s time for action, not theories.

Barki is now pursuing a master’s degree in energy systems engineering with an interest in developing technologies for rechargeable, solar powered batteries, but said he is inspired by energy researchers at ASU. He says he would like to continue conferring with ASU faculty once he returns home and work toward his doctorate.

“I have a new perspective,” he said. “Scientists explore space, but engineers build the telescopes.”

Farah Akram, who has a power electronics degree from NUST, did not let her poor sense of direction thwart her aspirations to pursue a master’s degree in electrical power engineering. “The ASU campus is so big that I got completely lost on my first day,” she said, explaining that her campus at NUST was small in comparison. “But everyone was so helpful, and eventually I found my way.”

The majority of Akram’s family is in business and she, who describes herself as “extremely organized,” is the only engineer. “Our family is passionate about education,” she said. “Engineering made the most sense for me.”

Farah Akram explains to members of the public what USAID’s mission is in Pakistan at Tempe Night of the Open Door. Photographer Erika Gronek/ASU

Farah Akram explains to members of the public what USAID’s mission is in Pakistan at Tempe Night of the Open Door. Photo by Erika Gronek/ASU

Cultural exchange

Unanimously, the students declared the Arizona Renaissance Festival their favorite cultural experience to date. They donned crowns along with other festival-goers and enjoyed the jousting knights, circus performers, musicians and the marketplace.

Actually, marketplaces of all sorts are of interest to the students. “We love shopping,” said Zahara, who says she’s particularly enjoyed Arizona Mills and Tempe Marketplace — both accessible via public transportation.

But more important than shopping and festivals are the opportunities to collaborate with other students.

“I feel so welcome — faculty has been extremely supportive,” Akram said. “This has been an unimaginable, new experience.”

“The cultural exchange has helped me learn how to socialize with people who are different,” says Barki. “One day on a trip via the light rail, a group of elderly ladies got on — so we stood up and gave them our seats. Everyone clapped. It was definitely a notable moment.”

Salahuddin noteed that the learning exchange extends well beyond American customs and culture. “We are not just meeting American students — there are students from five different countries working on one of my lab projects,” he said. “Exposure to these new, wide-ranging perspectives will be incorporated into the problem-solving processes we use when we return home.”

Terry Grant

Media Relations Officer, Media Relations and Strategic Communications

480-727-4058

ASU solar, sustainability scholar sojourns to Sweden


March 21, 2017

Though Arizona State University is committed to sustainability and renewable energy, weaning our civilization off fossil fuels and combating our changing climate is a much larger issue than the university can tackle on its own. Creating a truly sustainable world will take a global collaboration from researchers.

Electrical engineering Professor Meng Tao is one such researcher. He'll take his solar energy expertise to collaborate with Swedish researchers as the 2017 Fulbright Distinguished Chair in Alternative Energy Technology. As part of this $125,000 estimated package that includes a monthly allowance, housing assistance and airfare, Tao will work at the Chalmers University of Technology in Gothenburg, Sweden, for the 2017–2018 academic year. Portrait of Meng Tao Electrical engineering Professor Meng Tao has been awarded the 2017 Fulbright Distinguished Chair in Alternative Energy Technology, which will take him to Sweden's Chalmers University of Technology over the 2017–2018 academic year to study solar-powered charging for electric vehicles and solar module recycling. Photo courtesy of Meng Tao Download Full Image

“I hope to exchange ideas with my Swedish colleagues, to learn from one another, to stimulate new ideas and to facilitate long-term collaborations on some of the most pressing energy issues we are facing,” Tao said.

Tao is one of 45 Fulbright Distinguished Chairs awarded in 2017 to top scholars with exemplary teaching and publication records, many of whom are in the social sciences. The position is considered one of the most prestigious Fulbright Scholar Program appointments.

Douglas Cochran, who served as 2015 Fulbright Distinguished Chair in Science and Technology at the Australian Department of Defence’s Defence Science and Technology Group, said Tao’s appointment reflects favorably on ASU and the Ira A. Fulton Schools of Engineering.

“The Fulbright Distinguished Chair in Sweden will provide Professor Tao with an excellent platform for building a new base of international collaborators, affecting not only his own scholarly and educational activities but potentially extending to enduring ties between his broader circle of ASU and U.S. colleagues and their counterparts in Europe,” said Cochran, a fellow faculty member in the School of Electrical, Computer and Energy Engineering, one of the six Fulton Schools.

Tao’s research during his Fulbright Distinguished Chair appointment focuses on two areas: charging electric vehicles with solar energy and making solar modules more sustainable through value-added recycling.

Since the electric grid is largely powered by fossil fuels, Tao said electric cars lose their environmental benefit if they’re charged through the grid, but solar may hold the answer to this problem.

“Charging electric vehicles by solar electricity makes environmental sense, but it is still expensive and unreliable,” he said. “That’s why we are developing a new solar photovoltaic system for charging electric vehicles that reduces the cost of solar electricity by 30 percent while eliminating its intermittency.”

With the potential for more solar photovoltaic systems in place for charging electric vehicles and other uses, Tao hopes to make paying for photovoltaic module recycling more attractive.

“There are valuable and bulky materials in silicon solar modules such as solar-grade silicon, silver, aluminum and glass,” Tao said. “When properly recovered, they can generate enough revenue to allow a profitable recycling business without any subsidies. We are developing a technology to do just that.”

Tao, who is also a senior sustainability scientist at ASU’s Julie Ann Wrigley Global Institute of Sustainability, is looking forward to connecting the work done at ASU with that of Chalmers University of Technology.

“There is a wide range of research projects going on within the Fulton Schools and within ASU in the domain of energy, environment and sustainability,” Tao said. “I hope to be able to serve as a bridge and connect faculty and students of similar interests on two campuses for a broader collaboration across the Atlantic Ocean.”

For one week during Tao’s stay, one of his students will visit to help introduce the Fulton Schools’ work in these areas.

Sweden’s Chalmers University of Technology is an excellent fit for Tao’s Fulbright research proposal, especially the Swedish Electromobility Centre, a national Center of Excellence for hybrid and electric vehicle technology and charging infrastructure, and the Chalmers Competence Centre Recycling.

“The Swedish Electromobility Centre involves experts from all over Sweden and serves as a base for interaction between academia, industry and society. As an added bonus, major automaker Volvo is headquartered nearby,” he said. “The goal of the Chalmers Competence Centre Recycling is to be a network and catalyst for multidisciplinary R&D collaboration within the field of circular use of materials. Recycling is critical for a resource-efficient society.”

He hopes to spread knowledge of solar technology scalability and sustainability issues beyond Sweden to other European Union countries as well.

Beyond the engineering issues, he’s looking forward to learning about his new host country.

“I hope to learn a bit about the culture, history, geography and people of Sweden,” Tao said. “I hope to renew old relations, build new relations and make friends from all walks of life: college students, faculty members and average Joes in my neighborhood.”

He also finds it interesting to be a representative of the United States in a new country.

“As a first-generation immigrant, I was surprised when I received the notification,” he said. “I will represent, unofficially, the United States in a country that is neither my birth country nor my adoptive country. How fascinating this experience will be.”

First things first, Tao said, is getting ready for the Swedish climate.

“My wife and I are struggling to find suitable attire for the 2017 Nobel Award Ceremony and the long, cold winter in Sweden,” he says. “Phoenix is definitely not the best place for winter clothes.”

Monique Clement

Communications specialist, Ira A. Fulton Schools of Engineering

480-727-1958

UNAM team joins ASU power ‘boot camp’


March 10, 2017

The term “microgrid” may not conjure excitement in the average person, but for organizations or people that stand to lose money, life, limb or living standards due to power outages, it does.

Microgrids can keep the lights on even after main power sources fail and they were the focus of a week-long “boot camp” held at Arizona State University’s Polytechnic campus this week for military veteran students and an academic trio from Mexico City.   people working with solar panel UNAM doctoral students Fernanda Alvarez and Jose Fuentes, center (left to right), examine part of a microgrid solar-powered system alongside student veterans at Arizona State University’s Polytechnic campus, Wednesday, March 8, 2017, during the Microgrid Boot Camp. Photo by Peter Zrioka/ASU Download Full Image

Two doctoral students and a professor from the Universidad Nacional Autónoma de México (UNAM) joined the event organized by the Ira A. Fulton Schools of Engineering and part of the U.S. Navy’s NEPTUNE energy research project with ASU.  

“The microgrid boot camp is a 40-hour intensive, all-inclusive approach to microgrid education focusing on infrastructure basics,” said Nathan Johnson, assistant professor for the Fulton Schools at the Polytechnic campus and director of the Laboratory for Energy and Power Solutions. “This week and the involvement of UNAM is one example of how we’re taking our research and training to be a true global program. We’re on the early stages of developing global microgrid centers of excellence.”

NEPTUNE is an energy research project established with Department of Defense funding to break new ground in alternative energy while employing student veterans to assist and gain marketable skills. Veterans and other military-affiliated students are the primary audience but Johnson saw the benefit in having UNAM participate and continue the existing collaboration.

“For them to come up was more of a good opportunity,” Johnson said. “Given that UNAM and ASU have an exchange, this is part of their exchange to come work with us from an educational research standpoint. The work we’re doing with Cesár Angeles [UNAM lead professor], focuses on the problem of significant amount of solar on the grid. How do you effectively manage those with storage and advanced controls.”

Johnson said that part of the goal in partnering with UNAM is to develop energy simulations, hardware and then connecting them to “control the dial” and make sure it meets utilities’ safety and reliability requirements for one grid, and then for multiple ones connected together.  

The objective of using microgrids is to provide quality, reliable stand-alone energy during a loss of power from the main grid — i.e., the main electric power infrastructure. Microgrid systems, which can be powered by solar or other energy, are being installed in hospitals, military bases, college campuses and have become very common in data centers, Johnson said.  They can also be packaged and transported where needed during disaster response.

“So places that need to have 100 percent reliable power,” Johnson said. “They go down for seconds and it’s millions of dollars.  For many of the small businesses and household consumers, the focus is on renewable energy and reduced electric bills.”

The boot camp included interactive tours, lessons, lectures and talks from corporate and other ASU partners.  More importantly it enabled the exchange of perspectives and capabilities, a valuable aspect to the UNAM students.

“I’ve worked with photovoltaic systems, I’ve utilized these inverters, and utilized practically the same brand of panels, so it’s something that we know,” said UNAM doctoral electrical engineering student Jose Fuentes, about being familiar with some of the boot camp concepts and equipment. “What is interesting here is how easily the systems can be built and integrated quickly with the support needed to assemble everything and have it running within a semester or so.”

Another key aspect of the course is the focus on renewable energy, said Fernanda Alvarez, also a doctoral electrical engineering student at UNAM and a Colombia native. 

“There are many parts in Mexico, Colombia, here and other places where due to distance or location, there isn’t quality access to energy,” Alvarez said. “Systems like these will obviously make life easier and give everyone the rightful access to electricity and quality of life.”

The Micogrid Boot Camp is one of six NEPTUNE projects at ASU. The acronym stands for Naval Enterprise Partnership Teaming with Universities for National Excellence. Locally, the program is a collaboration between ASU LightWorks, the Ira A. Fulton Schools of Engineering and the Pat Tillman Veterans Center. 

Jerry Gonzalez

Media Relations Officer, Media Relations and Strategic Communications

 
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ASU, Stanford researchers achieve record-breaking efficiency with tandem solar cell

February 20, 2017

Some pairs are better together than their individual counterparts: peanut butter and chocolate, warm weather and ice cream, and now, in the realm of photovoltaic technology, silicon and perovskite.

As existing solar-energy technologies near their theoretical efficiency limits, researchers are exploring new methods to improve performance — such as stacking two photovoltaic materials in a tandem cell. Collaboration between researchers at Arizona State University and Stanford University has birthed such a cell with record-breaking conversion efficiency — effectively finding the peanut butter to silicon’s chocolate.

The results of their work, published Feb. 17 in Nature Energy, outline the use of perovskite and silicon to create a tandem solar cell capable of converting sunlight to energy with an efficiency of 23.6 percent, just shy of the all-time silicon efficiency record.

“The best silicon solar cell alone has achieved 26.3 percent efficiency,” said Zachary Holman, an assistant professor of electrical engineering at the Ira A. Fulton Schools of Engineering. “Now we’re gunning for 30 percent with these tandem cells, and I think we could be there within two years.”

Silicon solar cells are the backbone of a $30 billion-a-year industry, and this breakthrough shows that there’s room for significant improvement within such devices by finding partner materials to boost efficiency.

The high-performance tandem cell’s layers are each specially tuned to capture different wavelengths of light. The top layer, composed of a perovskite compound, was designed to excel at absorbing visible light. The cell’s silicon base is tuned to capture infrared light.

Perovskite, a cheap, easily manufacturable photovoltaic material, has emerged as a challenger to silicon’s dominance in the solar market. Since its introduction to solar technology in 2009, the efficiency of perovskite solar cells has increased from 3.8 percent to 22.1 percent in early 2016, according to the National Renewable Energy Laboratory.

The perovskite used in the tandem cell came courtesy of Stanford researchers — professor Michael McGehee and doctoral student Kevin Bush, who fabricated the compound and tested the materials.

The research team at ASU provided the silicon base and modeling to determine other material candidates for use in the tandem cell’s supporting layers.

Overcoming challenges with perovskites

Though low-cost and highly efficient, perovskites have been limited by poor stability, degrading at a much faster rate than silicon in hot and humid environments. Additionally, perovskite solar cells have suffered from parasitic absorption, in which light is absorbed by supporting layers in the cell that don’t generate electricity.

“We have improved the stability of the perovskite solar cells in two ways,” said McGehee, a materials science and engineering professor at Stanford’s College of Engineering. “First, we replaced an organic cation with cesium. Second, we protected the perovskite with an impermeable indium tin oxide layer that also functions as an electrode.”

Though McGehee’s compound achieves record stability, perovskites remain delicate materials, making it difficult to employ in tandem solar technology.

“In many solar cells, we put a layer on top that is both transparent and conductive,” said Holman, a faculty member in the School of Electrical, Computer and Energy Engineering. “It's transparent so light can go through and conductive so we can take electrical charges off it.”

This top conductive layer is applied using a process called sputtering deposition, which historically has led to damaged perovskite cells. However, McGehee was able to apply a tin oxide layer with help from chemical engineering professor Stacey Bent and doctoral student Axel Palmstrom of Stanford. The pair developed a thin layer that protects the delicate perovskite from the deposition of the final conductive layer without contributing to parasitic absorption, further boosting the cell’s efficiency.

The deposition of the final conductive layer wasn’t the only engineering challenge posed by integrating perovskites and silicon.

“It was difficult to apply the perovskite itself without compromising the performance of the silicon cell,” said Zhengshan (Jason) Yu, an electrical engineering doctoral student at ASU.

Silicon wafers are placed in a potassium hydroxide solution during fabrication, which creates a rough, jagged surface. This texture, ideal for trapping light and generating more energy, works well for silicon, but perovskite prefers a smooth — and unfortunately reflective — surface for deposition.

Additionally, the perovskite layer of the tandem cell is less than a micron thick, opposed to the 250-micron-thick silicon layer. This means when the thin perovskite layer was deposited, it was applied unevenly, pooling in the rough silicon’s low points and failing to adhere to its peaks.

Yu developed a method to create a planar surface only on the front of the silicon solar cell using a removable, protective layer. This resulted in a smooth surface on one side of the cell, ideal for applying the perovskite, while leaving the backside rough, to trap the weakly absorbed near-infrared light in the silicon.

“With the incorporation of a silicon nanoparticle rear reflector, this infrared-tuned silicon cell becomes an excellent bottom cell for tandems," said Yu.  

Building on previous successes

The success of the tandem cell is built on existing achievements from both teams of researchers. In October 2016, McGehee and post-doctoral scholar Tomas Leijtens fabricated an all-perovskite cell capable of 20.3 percent efficiency. The high-performance cell was achieved in part by creating a perovskite with record stability, marking McGehee’s group as one of the first teams to devote research efforts to fabricating stable perovskite compounds.

Likewise, Holman has considerable experience working with silicon and tandem cells.

“We’ve tried to position our research group as the go-to group in the U.S. for silicon bottom cells for tandems,” said Holman, who has been pursuing additional avenues to create high-efficiency tandem solar cells.

In fact, Holman and Yu published a comment in Nature Energy in September 2016 outlining the projected efficiencies of different cell combinations in tandems.

“People often ask, ‘Given the fundamental laws of physics, what’s the best you can do?’” said Holman. “We’ve asked and answered a different, more useful question: Given two existing materials, if you could put them together, ideally, what would you get?”’

The publication is a sensible guide to designing a tandem solar cell, specifically with silicon as the bottom solar cell, according to Holman.

It calculates what the maximum efficiency would be if you could pair two existing solar cells in a tandem without any performance loss. The guide has proven useful in directing research efforts to pursue the best partner materials for silicon.

“We have eight projects with different universities and organizations, looking at different types of top cells that go on top of silicon,” said Holman. “So far out of all our projects, our perovskite/silicon tandem cell with Stanford is the leader.”

Pete Zrioka

Communications specialist , Office of Knowledge Enterprise Development

480-727-5631

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