Analysis of Interfacial Losses and Passivation Strategies for Narrow‐Bandgap Perovskite Solar Cells

Tin‐lead (Sn–Pb) halide perovskites hold promise as narrow‐bandgap semiconductors in future solar cells. Currently, non‐radiative recombination induced open‐circuit voltage losses limit their full potential. To determine their origin, intrinsic and interfacial non‐radiative recombination losses are investigated for Sn–Pb perovskite solar cells, and the effects of bulk and surface passivation strategies are assessed. Absolute photoluminescence is used to determine the quasi‐Fermi level splitting in perovskite layers, with and without charge transport layers, and distinguish bulk and interface contributions. The intrinsic losses in the perovskite semiconductor and at its interfaces with the poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and C 60 charge transport layers contribute significantly to the overall voltage deficit. Incorporating glycine hydrochloride as bulk additive during processing reduces the non‐radiative losses in the absorber. Likewise, surface passivation with alkane‐diammonium iodides or cadmium iodide mitigates the non‐radiative recombination induced by the C 60 electron transport layer by eliminating direct contact with the perovskite semiconductor. While each of these passivation strategies are beneficial, shortcomings remain in implementing them in actual devices because effective passivation of the perovskite can limit the efficient extraction of charges.