Optimization of postproduction heat treatment for plastic solar cells

We present this detailed study of a postproduction heat treatment of flexible organic solar cells based on regio-regular (RR) P3HT:PCBM composite in a wide temperature range from 75°C to 150°C. The efficiency of the photovoltaic device was significantly improved by postproduction heat treatment and both optimal annealing temperature and time dependencies were determined. Optimized parameters yielded >3% efficiency for devices on glass substrates and, using these optimized parameters, an efficiency of >2% was found for devices fabricated on flexible substrates. The optimal phase separation of PCBM and RR-P3HT into bi-continuous network structure occurs within a very short period of time and are very stable. We found that optimal concentration of PCBM in a RR-P3HT matrix is rather low, only 34 w.%. We show the performance of plastic solar cells fabricated on flexible substrates (ITO coated PET) using these optimized heat treatment parameters.