Lab profile: Section for Solar Energy, DTU

Fast, cheap, and thin: Low cost solar power for all

Solar panels are a common sight on rooftops around the world. But while generating green electricity cheaply is of great benefit to the developed world, the ability to harness the power of the sun could be transformative for those without any access to a regular electricity supply. Low-cost, solar power for all, based on thin, flexible polymer cells that can be manufactured quickly and easily using regular printing processes, simple equipment, and abundant materials is the aim of Danish scientist Frederik C. Krebs. His lab, the Section for Solar Energy (SOL) at the Technical University of Denmark (DTU), aims to speed up the progress of polymer solar cell technology with an innovative, holistic approach.

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Materials Today takes a closer look...

“It is all about the idea of printed electronics,” he explains. “Printing enables the integration of many discrete functionalities into one device. Integration is key – enabling infinite complexity infinitely fast.”

Krebs’s lab is not just exploring the underlying science and developing new materials and designs for printed polymer solar cells. SOL has also been highly successful in demonstrating the practicalities of polymer solar cells and promoting their development in novel ways.

Two years ago, SOL launched a cheap, easy-to-produce solar module that was made freely available to academics, students and even school children. While the freeOPV module was far from mark when it comes to power conversion efficiency, admits Krebs, the concept was to make the technology as accessible and open to all as possible.

Kreb’s lab has also created its own 1000 m² solar park test site using in-house developed solar cells, which can be installed (and removed) at a rate of 100 m per minute – much faster than conventional solar technologies.

Materials Today spoke to Lead professor Frederik C. Krebs, to find out more about his lab...

How long has the group been running?

The Section for Solar Energy has been running for 15 years at DTU since 2001.

How large is the group?

The group is made up of 30 staff including scientists, engineers, postdocs, and PhD students.

What are the major themes of research?

SOL is focused on organic photovoltaics (OPV), printed organic and polymer solar cells, and perovskite solar cells. Printing methods for light-emitting electrochemical cells, electrochromics, transistors, batteries, and fuel cells are also being explored. Solar cell research efforts range from designing new light-harvesting materials and stacked solar cells to the industrial roll-to-roll processing of polymer devices and panels for large-scale energy production for the grid.

“We use generic materials, generic equipment, and generic printing techniques to approach the integration of solar cells in a completely new way,” says Krebs. “I believe in scaling! If a potential technology does not have infinite scaling potential then it will never make a difference.”

How and why did you come to work in these areas?

“I am an organic chemist in my heart but a multidisciplinary scientist to the bone,” says Krebs.

He has directed his research towards organic solar cells because an organic chemist can design molecules for any purpose, and solar energy conversion is a challenging and rewarding mission, Krebs explains.

“Energy has been on the agenda for a long time,” he says. “Scientists have to make their work matter to real people, the results should be good for society and have a positive impact.”

What facilities and equipment does your lab have?

The Characterization Laboratory for Organic Photovoltaics (CLOP) has standardized performance testing equipment including a class A solar simulator, IPCE testing, 1000 h lifetime testing using thermal cycling and weathering chambers, and outdoor testing facilities. SOL has several industrial-scale roll-to-roll (R2R) processing lines including flexo printing, rotary screenprinting, slot-die, inkjet, and inspection equipment. Further laboratories provide facilities for polymer synthesis, ink development, materials characterization, and prototype fabrication using mini roll coaters (MRC).

Do you have a favorite piece of kit/equipment?

“No! I am not ‘in love’ with any one piece of equipment or technique,” says Krebs. “It’s just a tool for the scientist.”

What is the key to running a successful lab?

“I am an active researcher and I spend a lot of time in the lab,” says Krebs. “I believe in the concerted effort of the many, so I set the targets and the goals but the lab has a very flat structure. We have a shared objective and agenda, but I trust in my team members – it is a team effort.”

How do you plan to develop the lab in the future?

“So far, we have worked on the ‘can we’ questions about flexible solar cells,” says Krebs.

He believes that those questions have been answered with a resounding ‘yes’, so the next step is to develop and test actual devices. It will be a natural progression to put the science to work in real life, says Krebs.

“As a scientist, I must make my research matter to real people,” says Krebs. “I want our work to be good for society and have a positive impact. Our solar cell technology could have a major, transformative impact on people who have very little. This is what matters.”

Most influential publications

• F. C. Krebs, N. Espinosa, M. Hösel, R. R. Sondergard, M. Jorgensen. Rise to Power – OPV-based solar parks. Adv. Mater. (2014) 26, 29-39, http://dx.doi.org/10.1002/adma.201302031
• F. C. Krebs, S. A. Gevorgyan, J. Alstrup. A roll-to-roll process to flexible polymer solar cells: model studies, manufacture and operational stability studies. J. Mater. Chem. (2009) 19, 5442-5451,  http://dx.doi.org/10.1039/B823001C
• F. C. Krebs, Fabrication and processing of polymer solar cells: A review of printing and coating techniques. Sol. Energy Mater. Sol. Cells (2009) 93, 394-412, http://dx.doi.org/10.1016/jsolmat.2008.10.004
• F. C. Krebs, M. Hösel, M. Corazza, B. Roth, M. V. Madsen, S. A. Gevorgyan, R. R. Sondergard, D. Karg, M. Jorgensen. Freely available OPV – The fast way to progress. Energy Technology (2013) 1(7), 378–381, http://dx.doi.org/10.1002/ente.201300057

Recent publications

• M. Hösel, H. F. Dam, F. C. Krebs. Development of lab-to-fab production equipment across several length scales for printed energy technologies, including solar cells. Energy Technology (2015) 3, 293-304, http://dx.doi.org/10.1002/ente.201402140
• T. R. Andersen, et al. Scalable, ambient atmosphere roll-to-roll manufacture of encapsulated large area, flexible organic tandem solar cell modules. Energy & Environmental Science (2014) 7, 2925-2933, http://dx.doi.org/10.1039/c4ee01223b
• M. Jorgensen, et al. The state of organic solar cells – A meta analysis. Solar Energy Materials & Solar Cells (2013) 119, 84–93, http://dx.doi.org/10.1016/j.solmat.2013.05.034 

Further information

http://www.plasticphotovoltaics.org/
http://www.sol.energy.dtu.dk/
http://www.energy.dtu.dk/
http://www.clop.dk/