Associate Professor Ergang Wang.​​​​​
Photo: Knut and Alice Wallenberg Foundation

Polymer solar cells, new Wallenberg Academy Fellow project

Solar cells are predicted to play an important role in reaching a sustainable energy production, but a problem with the silicon based is their complicated manufacture process. Associate Professor Ergang Wang receives funding as a Wallenberg Academy Fellow to develop polymer solar cells that are bendable and easy to produce.
Organic solar cells, OSCs, normally consist a polymer as donor and a fullerene derivative as acceptor in the active layer. However, the fullerene derivate, which is the most common acceptor, cannot guarantee high enough efficiency and stability of OSCs to change the solar power market. As a Wallenberg Academy Fellow Ergang Wang will explore another, fullerene-free path for the OSC.
“This fellowship gives me freedom to explore the fields where I believe a solution may exist. It is of course an honour to become a Wallenberg Academy Fellow and a great feeling to finally get it. You should never give up!” he says.
OSCs have the advantages of light-weight, low cost and fast high-volume production. They are also believed to have little environmental impact. Due to the promise of OSCs, many countries have invested heavily in the research and development of OSCs with the aim of commercializing them. As a result, the development of OSCs has been significant with efficiencies improving from 1 percent to over 14 percent in the last two decades. Still the technology is not yet ready for practical applications.

Fullerenes are football shaped molecules that have many good characteristics in many applications. In many OSCs of today they are used as acceptors in the cell’s active layer. The problem, however, is low stability caused by molecular diffusion, weak absorption in solar spectrum region, high cost and high-energy consumption required to produce fullerene derivatives themselves. Therefore, in order to boost the efficiency and stability of OSCs, there is a strong need to replace fullerenes as the acceptors in OSCs.
“For long researchers have tried to improve the fullerenes to be optimised for the OSCs. I want to try a different path. I want my OSCs to be independent from the limitations of fullerenes,” says Ergang Wang.
Ergang Wang and his group have already come far in the development of solar cells only consisting of polymers in the active layer. They have reached an efficiency of nine percent with a blend based on three polymers. They are very light and easy to produce in big roll-to-roll printing machines, kind of like the ones than newspapers are produced in. The major issue now is to get a better stability and efficiency.
“I believe that we are on the right track and my vision is that we, because of the funding, may be able to create a prototype with the right efficiency and stability to be able to start collaborations with industry.”
Ergang Wang thinks there is a great interest for breakthroughs in this kind of technology since it is sustainable both ecologically and economically. His goal is to reach towards an efficiency of around fifteen percent, which is a figure he says may make OSCs profitable and competitive in the market.
“The silicon cells will be more efficient for a long time forward but OSCs will be more cost effective in the long run. In ten years we may have reached far enough to have the technology on the market with for example polymer solar cells that you may put on your window or at the roof top,” says Ergang Wang.
The funding for the Wallenberg Academy Fellowship is SEK 7.5 million over five years with a possible extension of five more years. In addition Chalmers will fund the fellowship with another SEK 5 million for five years. 
Text: Mats Tiborn

Published: Thu 14 Dec 2017. Modified: Tue 09 Jan 2018