Stabilizing Metal Oxide Free n-i-p Perovskite Solar Cells by Electron-Transporting, Strong-Dipole Self-Assembled...

Metal oxides are widely used as electron-transporting layers in n-i-p perovskite solar cells (PSCs). However, their intrinsic disadvantages constrain device efficiency and stability. Here, we report a self-assembled molecule (SAM), 3-cyanopropionic acid (CPA), as an alternative to SnO2. The carboxyl (-COOH) group of CPA anchors firmly to the fluorine-doped tin oxide (FTO) substrate via stable covalent bonds, while the cyano (-CN) group enables vertical molecular assembly on FTO. This leads to the formation of an interfacial dipole that favors energy-level alignment and promotes efficient electron extraction. Furthermore, CPA modulates perovskite crystallization, reduces the lattice strain, and enhances interfacial contact. As a result, we achieve a champion power conversion efficiency of 25.17%, which is the highest reported value for metal oxide free n-i-p PSCs to date. Notably, unencapsulated devices also exhibit a remarkable enhancement in long-term storage stability, retaining approximately 90% of its initial PCE after 2500 h of storage in a nitrogen-filled glovebox.