Cathode interlayer-free organic solar cells with enhanced device performance upon alcohol treatment

An organic solar cell (OSC) usually contains a cathode interlayer (CIL) to enhance the device performance. However, if a cell without a CIL (CIL-free) still shows high performance, the cost of the cell can be reduced. In this study, we demonstrate that methanol soaking of the active layers is efficient to improve the performance of porphyrin small molecule-based bulk heterojunction photovoltaic devices. Compared with the CIL-free devices without treatment, the champion power conversion efficiency (PCE) of the CIL-free OSCs upon 15 s MeOH soaking treatment is improved by 18.7% from 7.55% to 8.96%. The PCE is even higher than those of the devices with widely used PFN-Br cathode interlayers (PCE: 8.55%) (PFN-Br: (poly[(9,9-bis(3 '-((N,N-dimethyl)-N-ethylammonium)-propyl)-2,7-fluorene)-alt-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]dibromide). Methanol soaking of the active layers improves the exciton dissociation and charge carrier transport and collection in the devices. This work provides a simple approach for preparing highly efficient CIL-free organic solar cells, which can be beneficial for large-scale and commercial applications.