Influence of P3HT molecular weight on film processing and solar cell performance

Here, the influence of molecular weight (Mw) of P3HT on film morphology, film processing, and BHJ performance were investigated. The film morphology of Mw=10000 P3HT film is asperous, which corresponds to the relatively low device performance. The donor ratio of BHJ based on P3HT Mw=700000 at 10:7 (donor:acceptor) achieves the best photovoltaic performance. And the BHJs with various P3HT Mw (from 10000 to 700000) demonstrates that P3HT Mw=50000 achieves the highest power conversion efficiency probably due to the appropriate chain length thus good film morphology and donor-acceptor interface contact. Although large Mw P3HT has strong light absorption, however, the ropy solution limits the film fabrication. Therefore, relatively large but not too large Mw for donor polymer is suitable for polymer solar cells. The results show that the Mw of P3HT plays no large role in the device stability.