Elegant Face-Down Liquid-Space-Restricted Deposition of CsPbBr3 Films for Efficient Carbon-Based All-Inorganic Planar Perovskite Solar Cells

It is a great challenge to obtain the uniform films of bromide-rich perovskites such as CsPbBr3 in the two-step sequential solution process (two-step method), which was mainly due to the decomposition of the precursor films in solution. Herein, we demonstrated a novel and elegant face-down liquid-space-restricted deposition to inhibit the decomposition and fabricate high-quality CsPbBr3 perovskite films. This method is highly reproducible, and the surface of the films was smooth and uniform with an average grain size of 860 nm. As a consequence, the planar perovskite solar cells (PSCs) without the hole-transport layer based on CsPbBr3 and carbon electrodes exhibit enhanced power conversion efficiency (PCE) along with high open circuit voltage (VOC). The champion device has achieved a PCE of 5.86% with a VOC of 1.34 V, which to our knowledge is the highest performing CsPbBr3 PSC in planar structure. Our results suggest an efficient and low-cost route to fabricate the high-quality planar all-inorganic PSCs.