Interface Passivation and Energy Level Alignment for Enhanced Photovoltage and Stability of Inverted Perovskite Solar Cells Using a Multifunctional Molecule

Abstract

Voltage loss induced by surface defects at the interfaces of perovskite is one of the key factors limiting further efficiency improvements in inverted perovskite solar cells (PSCs). Tailoring the uncoordinated bonds at perovskite surfaces can effectively suppress defects thereby enhancing charge transport and overall device performance of PSCs. In this study, L-tryptophan methyl ester hydrochloride (L-TMeCl) is employed to passivate the top interface of the perovskite. The protonated primary amine (R₁NH₃⁺) and the carboxylate ester (R₂COOCH₃) groups of L-TMeCl function as electron pair acceptors and donors, respectively, facilitating interactions with the negative and positive dangling bonds of the perovskites. As a result, the L-TMeCl-treated perovskite films exhibit enhanced n-type characteristics, improved energy level alignment, and reduced nonradiative recombination losses. This leads to the best performing PSC with a power conversion efficiency (PCE) of 24.73%, an enhanced open-circuit voltage (V_OC) of 1.17 V, and a decreased V_OC loss of 92.3 mV. Furthermore, due to the hydrophobic fused-ring core in L-TMeCl, the unencapsulated L-TMeCl-treated PSCs exhibit excellent storage stability, retaining 92.6% of their initial PCE after 1200 hours in air at 30±5% relative humidity, and 84.8% of their initial PCE after 510 hours of thermal annealing at 80°C. The use of multifunctional molecule provides an effective approach to fabricating high-performance and stable inverted PSCs.