Development of Semiconducting Polymers for Solar Energy Harvesting

Semiconducting polymer solar cells are an attracting class of devices for low-cost solar energy harvesting. The bulk hetero-junction structure based on composite materials of semiconducting polymer donor and fullerene acceptor is an effective form of active layers for polymer solar cells. So far, the limiting factors for widespread, practical applications in polymers solar cell is their low power conversion efficiency (PCE) and potential instability under light exposure. Thus new polymeric materials with desired properties and stability are crucial for improving the solar cell performance. Numerous conjugated polymers, such as poly[phenylene vinylene]s (PPVs) and polythiophenes, have been explored for this purpose, which lead to PCE as high as 5%. To improve the performance, low bandgap polymers and polymers with low lying HOMO energy levels have been the subject of recent focus. Efficiencies close to 8% have been achieved in the polymer system composed of thieno[3,4-b]thiophene and benzodithiophene alternating units (PTB). The high efficiency is due to the synergistic combinations of desired properties in the polymer system through detailed fine-tuning of the polymer structure. The recent results reaffirmed the notion that better solar cell polymers could be further developed for vital applications in real devices.