High-performance inverted polymer solar cells without an electron extraction layer via a one-step coating of cathode buffer and active layer

Low cost and efficient processing are key factors to be considered for the future practical application of polymer solar cells (PSCs). Herein, we report a novel strategy for the fabrication of high performance inverted PSCs via a simple one-step coating of the mixture of an amino-functionalized n-type small molecule POF-N and the active layer to simultaneously form the active layer and cathode interlayer. Interestingly, the inverted device based on one-step coating yielded enhanced or comparable power conversion efficiency (PCE) for fullerene, non-fullerene and polymeric acceptor based solar cells. The underlying mechanism was disclosed to be that POF-N preferred to aggregate closely on the indium tin oxide (ITO) surface during the coating process and served as the electron transport layer. Electron spin resonance spectra and space-charge-limited charge mobility tests showed that the electron mobility of the active layer was obviously enhanced due to the efficient doping interaction between POF-N and PC71BM. Consequently, the balanced charge transport contributed to the increased short-circuit current of the device. Our universal results, based on different systems, provide a promising device structure and design concept to reduce the cost of efficient PSCs.