An unfused-ring acceptor enabling ∼12% efficiency for layer-by-layer organic solar cells

Cost-effective acceptors and device fabrication processes are decisive factors for commercializing organic solar cells (OSCs). Herein, a simple unfused-ring electron acceptor (ThPF-4F) cored with 3,4-bis(3-fluoro-4-methylphenyl)thiophene has been developed for layer-by-layer (LBL) high-efficiency OSCs. PBDB-T was selected as the donor and a non-orthogonal solvent system was used to fabricate the device. LBL OSCs (PBDB-T/ThPF-4F) exhibit a better vertical gradient distribution of a donor and an acceptor in the active layers than bulk-heterojunction (BHJ) ones (PBDB-T:ThPF-4F) as revealed by film-depth-dependent light absorption spectroscopy. The charge transport was thus facilitated with reduced recombination losses during charge transfer. LBL OSCs deliver a maximum power conversion efficiency (PCE) of 11.83% with a higher short-circuit current and fill factor in comparison to the optimized BHJ counterparts (11.10%). Importantly, the PCE of LBL OSCs is further improved to 11.97% by adding 10 wt% PC71BM in the PBDB-T layer. This work demonstrates the integration of the rational molecular design and facile device processing as a promising strategy to develop high-performance cost-effective OSCs.

Automated summary

In this study, a simple unfused-ring electron acceptor (ThPF-4F) was developed for high-efficiency layer-by-layer (LBL) organic solar cells (OSCs). Compared to conventional bulk-heterojunction (BHJ) OSCs, LBL OSCs showed a better vertical gradient distribution of the donor and acceptor in the active layers, resulting in improved charge transport efficiency. The performance of LBL OSCs was further enhanced by adding 10 wt% PC71BM in the donor layer.