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. Disordered stacking and tangled dipoles at hole-selective interfaces limit charge transport and raise energy losses in perovskite solar cells. Xie et al. added bismuth oxychloride to order dipoles, exchange chlorine with iodine, and boost efficiency and stability.