Hot-Air Treatment-Regulated Diffusion of LiTFSI to Accelerate the Aging-Induced Efficiency Rising of Perovskite Solar Cells

Perovskite solar cells (PSCs) with LiTFSI-doped Spiro-OMeTAD as the hole transport layer (HTL) generally require aging in the air to achieve high efficiency (a.k.a. aging-induced efficiency rising), but attention is rarely paid to the synergistic effects of temperature and humidity during the ambient aging. In this work, based on the understanding of the doping mechanism of Spiro-OMeTAD, we develop an ambient condition-controlled hot-air treatment (HAT) for such kinds of PSCs to further improve the device efficiency and relieve the photocurrent hysteresis. After storing the PSCs at a temperature of 35-40 degrees C and humidity of 35-40% RH for 30 min, efficient redistribution of LiTFSI in Spiro-OMeTAD enables much-increased conductivity due to the increased concentration of Spiro-OMeTAD(+)center dot O-2(-) and Spiro-OMeTAD(+)center dot TFSI-, leading to an enhanced fill factor. From the light intensity-dependent V-oc and capacitance-voltage measurements, the Voc enhancement is proven to be originated from the change in dominant recombination type from trap-assisted interfacial recombination to bulk Shockley-Read-Hall recombination and the improved carrier dynamics at the perovskite/HTL interface. Furthermore, the decreased density and migration of shallow-level charge traps result in the negligible hysteresis of treated devices. Our work provides new insights into the effect of ambient aging on PSCs with SpiroOMeTAD and reveals the potentials of HAT to improve the device performance.