Solution-processed and evaporated C60 interlayers for improved charge transport in perovskite photovoltaics

Interlayers can strongly influence the interfaces of perovskite solar cells (PSCs), and significantly increase the cells’ stabilized power conversion efficiencies (PCEs). This study compares for the first time the fabrication of C60 interlayers, deposited either by solution-processing or vacuum-based thermal evaporation, at the interface between a SnO2 electron transport layer (ETL) and the perovskite (MAPbI3-xClx) absorber layer in a n-i-p architecture. We evaluate the influence of the C60 deposition method on the perovskite crystallization dynamics and relate it to the device performance. With an optimized C60 layer, the devices exhibit an improvement in the stabilized PCE along with reduced hysteresis. As a result, we achieve improvement from 12.5% to 17.3% on the stabilized PCE of the PSCs. Furthermore, we investigate the influence of the C60 layer thickness on the transport dynamics through time-resolved photoluminescence and transient absorption measurements. Finally, we demonstrate that the C60 interlayers stabilize the constant power output of the solar cells over time due to the reduction in charge carrier accumulation at the ETL/Perovskite interface. Our results indicate that the ETL/perovskite interface is a governing factor in the reduction of hysteresis and in the extension of the stability in the PSCs.