Spectroscopic Correlation of Interfacial Electronic Structures with Voltage-Loss Trends in Perovskite Solar Cells

Abstract

Interfacial energy loss remains a key limitation to further improvements in perovskite solar cells because the electronic structures at buried interfaces can differ substantially from those of isolated films. The effects of molecular doping of charge transport layers on interfacial energetics, carrier dynamics, and voltage loss are investigated in perovskite solar cell stacks. Two representative systems are studied: F4TCNQ-doped Spiro-OMeTAD as a p-type hole transport layer in regular n-i-p stacks, and DMBI-doped PCBM as an n-type electron transport layer in inverted p-i-n stacks. The results show that the reported open-circuit voltage trends cannot be explained by conductivity enhancement alone. For F4TCNQ-doped Spiro-OMeTAD, a smaller vacuum-level shift is observed at the perovskite/Spiro-OMeTAD interface, together with carrier-decay changes that are consistent with changes expected for reduced interfacial charge accumulation and recombination. In inverted stacks, the effect of DMBI-doped PCBM is more complex because the interfacial energy alignment is altered under illumination. The observations provide a spectroscopic basis for interpreting the reported voltage-loss trends, while the microscopic origin of the measured interfacial shifts cannot be determined uniquely from ultraviolet photoelectron spectroscopy (UPS) alone.