Chemically coupled dual-interface self-regulation for perovskite solar cells

Roughness and fragility of bottom-up interfaces in perovskite solar cells accelerate device degradation and increase maintenance costs, while conventional interface engineering often fails to address issues at multiple interfaces simultaneously. Here, trimethyl(cyanomethyl)ammonium iodide is employed for a dual-interface self-regulation. Solution containing this molecule selectively desorbs non-covalently bonded self-assembled molecules, facilitating deprotonation of P−OH groups on self-assembled molecules. The resulting −PO− headgroups undergo secondary homogeneous assembly, converting weakly adsorbed self-assembled molecules into stable bonded P−O−metal species and reducing potential barriers in the bottom depletion region. Simultaneously, trimethyl(cyanomethyl)ammonium iodide is extracted to the perovskite surface, spontaneously forming a one-dimensional n-type capping layer with a robust edge-sharing skeleton and enhancing quasi-Fermi level splitting at the interface. This coupled interfacial reinforcement leads to a high efficiency of 27.05% (certified 26.61%) and maintains over 95% of the initial efficiency after 2,100 hours of continuous operation at 65 °C. Wu et al. show that cooperative coupling at buried and top perovskite interfaces promotes chemically bonded self-assembled monolayers and forms a stable 1D heterojunction, enabling perovskite solar cells with 27.05% efficiency and maintaining over 95% of the efficiency after 2,100-hour continuous operation at 65 °C.