Evaluation of interfacial photophysical processes by time-resolved optical spectroscopy in perovskite solar cells

Enhancing the passivation of the perovskite (PVK)/charge transport layer interface is the primary strategy for minimizing losses in the open circuit voltage of PVK solar cells. We examined systems comprising half-stacks of hole transport layers (HTLs) deposited atop the mixed cation lead halide PVK photoactive layer (Cs0.05FA0.85MA0.1PbI3) using time-resolved photoluminescence and transient absorption spectroscopy. Photovoltaic devices were constructed to validate our findings, yielding power conversion efficiencies of up to 24%. Combining spectroscopic measurements reflected the complexity associated with interpretation of the kinetics as multiple processes overlap over time. The 2,2′,7,7′-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD) HTL resulted in low interface recombination and effective charge extraction, whereas poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) exhibited high interface recombination. The NiOx HTL passivated with [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) exhibited prolonged photoluminescence carrier lifetimes, signifying interface passivation through a Me-4PACz self-assembled monolayer. Theoretical calculations demonstrated an electrostatic interaction between Me-4PACz and the iodine vacancies at the PVK interface, indicating defect passivation.