Edge/Corner-Sharing 2D Perovskite Functional Layer for Efficient and Stable Inverted Perovskite Solar Cells.

Tuning the surface structure of perovskite films based on two-dimensional (2D) perovskites with narrow octahedral interlayer spacing is essential yet challenging to mitigate quantum and dielectric confinement, achieve interfacial energy-level matching, and promote efficient carrier transport kinetics in inverted perovskite solar cells (PSCs). Innovatively, an n-type 2D perovskite functional layer featuring a distinctive edge/corner-sharing (E/C-sharing) [PbI6]4- octahedral framework is constructed on a 3D film surface by utilizing N-methylethylenediamine cations (MEDA2+) to regulate the connection modes of [PbI6]4- octahedral units. Specifically, the 2D-MEDAPb2I6 with the E/C-sharing octahedra yields the narrowest interlayer spacing recorded to date (8.39 Å) among 2D perovskites, thus boosting the octahedral interlayer coupling effect and weakening the quantum and dielectric confinement effect to improve carrier mobility. Additionally, the 2D capping layer reinforces surface lattice stability by inducing a compressive stress field and increasing defect formation energy. The resulting type-II 3D/2D heterojunction significantly lowers the interfacial energy barriers for electron transfer and reduces the carrier recombination losses. Consequently, the inverted PSCs achieve an optimal efficiency of 26.43% (certified at 26.10%) and maintain over 94% of their initial efficiency after operating for 1200 hours under simulated AM 1.5G illumination. This research provides a unique perspective for developing novel 2D perovskites in perovskite-based photovoltaics.