Lewis BaseStrategy for Crystallization Control andBuried Interface Passivation on Hydrophobic PTAA Substrate for EfficientTin–Lead Perovskite and All-Perovskite Tandem Solar Cells

Nonionic PTAA is an ideal substitute for PEDOT:PSS as a hole-selective layer to improve the stability of mixed tin–lead (Sn–Pb) perovskite solar cells (PSCs). However, its hydrophobic nature aggravates the unbalanced crystallization and poor buried contacts of Sn–Pb perovskite films. Here, we report a Lewis base strategy to tackle these issues by introducing 4-bromophenylurea (BPU) or 4-bromophenylthiourea (BPSU) to interact with precursor ingredients to form large clusters, which accelerate nucleation and delay crystal growth as well as suppress buried interfacial nonradiative recombination. Compared to BPU, the more polar BPSU enables stronger interactions with Sn-halides than Pb-halides, resulting in improved film and interface qualities. Consequently, the Sn–Pb PSCs achieve a power conversion efficiency of 23.87%, the highest reported value for Sn–Pb cells on PTAA. Furthermore, the all-perovskite tandems deliver an efficiency of 27.61% (certified 27.17%) and retain 90% of their initial value after 1200 h of maximum power point tracking in nitrogen.