Interface passivation and energy level alignment for enhanced photovoltage and stability of inverted perovskite solar cells using a multifunctional molecule

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 (R 1 NH 3 + ) and the carboxylate ester (R 2 COOCH 3 ) 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 h in air at 30 ± 5 % relative humidity , and 84.8 % of their initial PCE after 510 h of thermal annealing at 80 °C. The use of multifunctional molecule provides an effective approach to fabricating high-performance and stable inverted PSCs. A multifunctional molecule, L-tryptophan methyl ester hydrochloride (L-TMeCl), was employed to enhance the perovskite quality and device performance. L-TMeCl can effectively passivate the surface defects by interacting with various defect sites, optimize energy level alignment at the perovskite/electron transport layer interface and alleviate the voltage loss from undesirable nonradiative recombination. Consequently, the L-TMeCl-treated device achieved an efficiency of 24.73 % with improved device stability. • A multifunctional passivation agent is used for perovskite solar cells . • Perovskite solar cells with passivation show an excellent efficiency of 24.73 %. • The optimized energy level alignment leads to a reduced voltage loss. • The perovskite solar cells with passivation exhibit improved thermal stability.