ESR Insights into PDINO-Modified Interfaces in Perovskite Solar Cells

Perovskite solar cell (PSC) development has achieved remarkable progress over the past decade. For further improvements in efficiency and stability, inserting cathode interlayers such as PDINO to modify the electron transporting layer (ETL)/metal cathode interface has proven effective in improving electron extraction in inverted PSCs. However, the microscopic mechanisms governing these effects remain insufficiently understood. For this study, we employ electron spin resonance (ESR) spectroscopy for direct observation of the charge states of ETL/PDINO/metal cathode structures in inverted PSCs. ESR measurements reveal electron diffusion from a Ag cathode to PC₆₁BM ETL through the PDINO layer by the contact formation between them, providing direct evidence that PDINO reduces the effective work function of Ag and facilitates Ohmic contact formation. In addition, systematic investigations with various ETLs and metal cathodes further clarify the relation between energy-level alignment and electron diffusion. These findings elucidate the microscopic charge-transfer processes induced by PDINO modification.