Self-assembled bilayer for perovskite solar cells with improved tolerance against thermal stresses

The adoption of perovskite solar cells (PSCs) requires improved resistance to high temperatures and temperature variations. Hole-selective self-assembled monolayers (SAMs) have enabled progress in the performance of inverted PSCs, yet they may compromise temperature stability owing to desorption and weak interfacial contact. Here we developed a self-assembled bilayer by covalently interconnecting a phosphonic acid SAM with a triphenylamine upper layer. This polymerized network, formed through Friedel–Crafts alkylation, resisted thermal degradation up to 100 °C for 200 h. Meanwhile, the face-on-oriented upper layer exhibited adhesive contact with perovskites, leading to a 1.7-fold improvement in adhesion energy compared with the SAM–perovskite interface. We reported power conversion efficiencies exceeding 26% for inverted PSCs. The champion devices demonstrated less than 4% and 3% efficiency loss after 2,000 h damp heat exposure (85 °C and 85% relative humidity) and over 1,200 thermal cycles between −40 °C and 85 °C, respectively, meeting the temperature stability criteria outlined in the International Electrotechnical Commission 61215:2021 standards.