Impact of PCBM/C60 electron transfer layer on charge transports on ordered and disordered perovskite phases and hysteresis-free perovskite solar cells

For perovskite solar cells, thermal treatment of perovskite/PCBM layer is typically required for facilitated charge extraction, thereby eliminating the notorious photocurrent hysteresis. However, a simple manufacturing process without additional heat treatment is desirable for low-cost production. Remarkably, we observed an absence of photocurrent hysteresis of perovskite solar cell with as-deposited PCBM/C60 layer. To understand what caused hysteresis-free photocurrent behaviors, PL quenching studies were conducted using time-resolved lifetime decays and deconvoluted PL analysis. It is found that the perovskite/PCBM layer, which was not thermally treated after deposition, led to inefficient defect passivation of grain boundaries (GBs) and defective domains at the perovskite interface. This led to charge trapping and detrapping events at the perovskite/PCBM interface, which caused the photocurrent hysteresis behaviors. In contrast, it is found that C60 diffused from the PCBM/C60 layer effectively passivated the perovskite GBs even without thermal treatment, which facilitated the charge transfer through GBs to electrodes and eliminated the photocurrent hysteresis. Our result provides a more economical manufacturing process without heat treatment of perovskite/PCBM layer while achieving defect passivation and high charge extraction efficiency of perovskite solar cells.