Extended Dual-Functional Engineering for High-Performance 2D Dion–Jacobson CsPbI ₃ Perovskite Solar Cells with Enhanced Stability

Two-dimensional (2D) CsPbI3 perovskite shows excellent prospects in the optoelectronics field, attributed to the superior phase stability compared to its 3D counterpart. However, it inherently faces quantum and dielectric confinement effects of the insulating bulky organic cations, leading to poor carrier transport kinetics. Here, we developed diamine cations [OEA, 2,2-oxybis(ethylamine)] and [EDBE, 2,2-(ethylenedioxy)bis(ethylamine)] with extended C–O chains for 2D Dion–Jacobson (DJ) CsPbI3 perovskites, aiming to avoid the undesirable charge tunneling barrier across the organic interlayer. Detailed characterization reveals that EDBE eliminates electron adsorption during interlayer transport, optimizing band alignment and enhancing the Pb-s orbital contribution at the valence band maximum (VBM), which leads to improved carrier lifetime. Through strategic molecular design, the extended dual-functional groups in EDBE strengthen hydrogen bonding and reduce interlayer distance, resulting in compact films with an enhanced carrier lifetime. More importantly, the EDBE spacer induces perovskite crystalline growth with a preferred vertical orientation and forms a multiphase distribution to facilitate carrier transport. Owing to these advantages, the optimized 2D DJ EDBECs4Pb5I16 solar cells deliver a champion power conversion efficiency (PCE) of up to 11.21%. Importantly, the devices exhibit exceptional stability, retaining 90% of their initial PCE after 720 h at 85 °C. It is believed that extended C–O chain engineering paves an effective route for solving carrier transport problems in 2D CsPbI3.