Organic Solar Cells' Efficiency Enhanced by Perylene Monoimide Phosphorus Salt Cathode Interfacial Layer

The composite high‐performance electrode is very important for excellent photoelectric devices. Interfacial modification is the dominating method to optimize electrode properties. Two easily synthesized perylene monoimide (PMI)‐derived organic phosphonium bromide salts are found interestingly valuable when they are applied as cathode interlayers (CILs) in bulk heterojunction (BHJ) organic solar cells (OSCs). Using the PBDB‐T:ITIC blend as the BHJ active layer in the inverted device structure, the power conversion efficiency (PCE) is greatly improved from 9.49% of the referenced device, which is without phosphonium CIL, to a PCE of 10.42% with PMI‐triphenyl‐phosphonium bromide (PMI‐TPP) and a PCE of 9.87% with PMI‐trimethoxylphenylphosphonium bromide (PMI‐TMOPP) as the CIL. Moreover, the two organic phosphonium bromide salts are also investigated by the traditional device structure, the PCE is 4.21% for the bare aluminum cathode referenced device, in contrast with a moderate increased PCE of 5.18% with PMI‐TPP CIL or a PCE of 5.05% with PMI‐TMOPP CIL. Therefore, the organic phosphonium bromide salt PMI‐TPP is a promising candidate of CIL material in OSCs.