Comprehensive and Comparative Analysis of Photoinduced Charge Generation, Recombination Kinetics, and Energy Losses...

In this work, a unique comprehensive and comparative analysis of photoinduced charge generation, recombination kinetics, and energy losses has been carried out to study the effect of different fullerene-based acceptors (FBAs) and nonfullerene acceptors (NFAs) on the performance of organic solar cells (OSCs). For this, different FBAs, specifically ICBA, PC60BM, and PC70BM, and NFAs, namely, ITIC, IT-4F, and IEICO-4F, were employed independently along with a particular donor polymer, PBDB-T, to fabricate bulk heterojunction OSCs and their performances have been compared. This donor molecule is known to give similar power conversion efficiency (PCE) with FBAs and NFAs and hence is ideal for comparative studies. The origin of the higher PCE of NFA-based OSCs vs FBA-based OSCs is analyzed in terms of spectral coverage, charge generation, recombination, and energy loss. It is found that the energy loss (ΔE_loss) is ∼0.8 to 1 eV for FBA-based OSCs, while it is 0.5-0.7 eV for NFA-based OSCs. Interestingly, for the PBDB-T:IEICO-4F-based system, energy losses due to charge generation (ΔE_CT) are ∼0 eV and therefore this system has minimum ΔE_loss among all of the studied devices. Providing a systematic, comprehensive, and comparative outlook, our study may further be extended to new upcoming NFA systems and beyond the donor system used in this work.