Efficient non-fullerene organic solar cells based on thickness-insensitive conjugated small molecule cathode interface

Abstract Interfacial engineering plays an essential role in the enhancement of device performance of organic solar cells (OSCs). Plentiful dopant-free electron- transporting materials have been effectively applied to modify ZnO in the inverted OSCs. However, these materials usually work with strict thickness, which observably limits their application in large area device fabrication. In this manuscript, an industrial small-molecule PyM with simply chemical structure solved in methyl alcohol was applied to modify ZnO in non-fullerene OSCs. PyM has good solubility in both methyl alcohol and chlorobenzene. Therefore, there is only a thin PyM layer left and distributed on the ZnO surface after coating the active layer. Meanwhile, a small amount PyM may be blended with the active layer near ZnO layer. The intense interaction between ZnO and PyM layer as well as the potential n-doping between PyM and the electron acceptor could modify the work function of ZnO and reduce the charge carrier recombination. Correspondingly, the inverted PBDB-T:ITIC OSCs with ZnO/PyM serving as electron transport layers achieve device power conversion efficiency (PCE) of 10.9% and 10.0% with 10 nm and 105 nm thick PyM film, respectively. The device performance is insensitive to the thickness of PyM. This phenomenon indicates that the PyM can be employed in roll-to-roll techniques to fabricate large-area devices at low cost. Similar results also emerged in PBDB-T:IT-M system, and the PCE was improved from 10.4% to 11.5% for ZnO and ZnO/PyM (~10 nm)-based devices.