Stacking-order-driven interfacial dipole flip and chlorine-iodine exchange for high-performance perovskite-organic tandem solar cells.

The physical adsorption of a self-assembled monolayer (SAM) onto an anchored layer introduces disordered stacking and a tangled dipole orientation at the hole-selective layer (HSL) surface, which affects the charge-transport dynamics and interface-driven energy loss in photovoltaic devices. Herein, we develop a collaborative strategy that combines stacking-order-driven interfacial dipole flipping with a chlorine-iodine exchange, achieved by depositing bismuth oxychloride (BiOCl) onto SAMs. This HSL exhibits a crystalline order characterized by dipole flipping and long-range periodic alignment in in-plane direction, driven by π-π interactions among carbazole units. It demonstrates enhanced stability against perovskite precursor solvents and thermal perturbations. The chlorine from BiOCl undergoes a chlorine-iodine exchange at the buried interface, modulating perovskite crystallization and weakening electron-phonon coupling. Our champion single-junction inverted perovskite solar cells (PSCs) achieve remarkable power conversion efficiencies (PCEs) of 27.25% (1.55 eV, 0.09 cm²) and 20.24% (1.85 eV, 0.09 cm²) with exceptional repeatability and operational stability. When employing SAMs/BiOCl as both HSL and interconnection layer, the champion perovskite-organic tandem solar cell (PO-TSC) attains an exceptional PCE of 28.14% (certified 27.84%) with steady power output of 27.86% (certified 27.59%). The device retains 90% of its initial efficiency under continuous maximum power point tracking with one-simulated-sun illumination over 600 hours.