The Role of Balanced Dual Charge Generation Pathways in Ternary Organic Solar Cells

Efficient charge generation and transfer is crucial for Organic Solar Cells (OSCs) to achieve high power conversion efficiency (PCE). The ternary strategy is commonly used to expand the absorption range of the device by utilizing comprehentary absorptions of three materials. However, the role of balanced electron transfermation and hole transfermation in the ternary OSC is rarely reported, although it is essential to improve the performance of the device. Here, we achieve a balanced photoinduced electron transfer process (PET) and photoinduced hole transfer (PHT) processes in PBDB-T:PC71BM:IT-M ternary OSCs, which is identified by the absorption, internal quantum efficiency (IQE) and photoluminescence (PL) quenching measurements. In addition, the VOC of the ternary devices is found to be increased with the ratio of IT-M, which is in good accordance with the “alloy model”, as revealed by the increased ECT estimated from the EL measurements. Therefore, the enhanced PHT from IT-M to PBDB-T is supposed to be a result of the deeper hybrid HOMO level of the “acceptors alloy”. As a result, along with enhanced absorption and optimized morphology, the charge generation and the transportation of the ternary device is improved, which increases JSC and FF of the devices. Therefore, this study proposed for the first time the mechanism of improving the PHT process due to the formation of acceptor alloys in ternary devices.The findings here are of great importance to understand the role of balanced dual charge generation pathways in ternary OSCs, providing potential methods to further improve the performance of materials and devices.