Low-dimensional/3D heterostructure boosts efficiency and stability of carbon-based CsPbI2Br perovskite solar cells

Hole-transport-layer-free (HTL-free) CsPbI2Br carbon-based all-inorganic perovskite solar cells (C-IPSCs) have attracted wide attention because of their low cost and moderate band gap. However, due to the direct contact between the carbon electrode and the perovskite, the surface defects of the perovskite film and the energy level mismatch seriously limit the improvement of power conversion efficiency (PCE). In this work, we systematically investigate the influence of surface modification by using benzoylcholine halide (BzChX; BzCh = benzoylcholine cation and X = I, Br, Cl) on CsPbI2Br perovskite films. The interaction between BzChX and perovskite films effectively passivates halogen vacancy defects and reduces non-radiation recombination. Simultaneously, a low-dimensional (LD)/three-dimensional (3D) heterostructure is formed on the surface of the perovskite films modified by BzChI and BzChBr, promoting the gradient energy level arrangement. Consequently, the PCE of HTL-free CsPbI2Br C-IPSCs after BzChI modification increases from 12.29% (control) to 14.15%, and the stability of the devices is also significantly enhanced.