Unraveling High Reproducibility and Broad Composition Tolerance in High-Efficiency Organic Solar Cells via Sequential Deposition

The reproducibility issue is impeding the progress of commercialization in organic photovoltaic (OPV) devices, as the difficulty in precise micro-nano structure control in bulk heterojunction films, as well as the ineluctable fluctuations of molecular weight and polydispersity index in the synthetic process. Due to such intrinsic properties, the poor regioregularity significantly affects the batch-to-batch variation in performance of large-area or integrative scattered OPV devices. Seeking alternatives as compensatory strategies is expected to reduce the inevitable problem of reproducibility in the fabrication process. Herein, the application potential of a pseudo-bilayer structure in high-performance OPVs, by using the solution-processed method is thoroughly examined, and it is observed that the sequentially-deposited solar cells enjoy improve device reproducibility in addition to the power conversion efficiency (PCE) enhancement. Importantly, such desirable reproducibility in layer-by-layer structures raised from the film formation process provides new opportunities in ternary OPV devices, and an improved PCE of 18.70% can be achieved in a PM6/L8-BO:PY-IT device, where the counterpart ternary cases exhibit a decreasing trend in performance with the increasing content of PY-IT. This work illustrates the spatial effects of pseudo-bilayer OPV devices in the aspect of charge carrier transport/transfer, morphology and film formation kinetics, and provides a novel perspective to overcome the barriers to commercialization. An improved device reproducibility in addition to the power conversion efficiency improvement can be achieved by a sequential deposited process for organic solar cells. The interpenetrating donor/acceptor interfaces and reduced surface roughness result in more uniform charge transfer, charge dissociation, and charge transport processes of layer-by-layer (LBL) films. Meanwhile, the LBL processed ternary devices exhibit broad third component tolerance.image