Non-Halogenated Solvent Processed Fullerene Free Ambient Stable Organic Solar Cells: Impact of Molecular Weight of New π-Conjugated Donor Polymer on Efficiency

Environmentally benign solvent-processed photoactive materials are urgently required to replace the current toxic solvent processing, especially for nonfullerene organic solar cells (NFOSCs). In this regard, we report an efficient new π-conjugated polymer (P1) for high performance NFOSCs. The careful choice of side chain, number-average molecular weight (Mn) tuning (low, medium, and high Mn, denoted as P12, P19, and P32), and dedicated device engineering of NFOSCs resulted an impressive device performance. Interestingly, P19-based NFOSCs achieved a high power conversion efficiency (PCE) of over 10% with nonhalogenated solvents, which is much superior than the P12- and P32-based NFOSCs. The high performance of P1-M-Mn polymer is very well correlated with its high short-circuit current density and fill factor values attained via well-defined active layer morphology. Moreover, the energy losses of the optimized devices are lower, which is very well correlated with the high Voc of the NFOSCs. Additionally, th...