Light Processing Enables Efficient Carbon-Based, All-Inorganic Planar CsPbIBr2 Solar Cells with High Photovoltages

Inorganic halide perovskite CsPbIBr2 possesses the most balanced band gap and stability characters among all of the concerned analogs for carbon-based, all-inorganic solar cells that are free of any hole-transporting layers and noble-metal electrodes. Yet, the current CsPbIBr2 solar cells seem to deliver the lowest record efficiency. This is originally plagued by a serious energy loss (E-loss) in the cells, which thus limits their open-circuit voltages (V-oc) severely. Herein, we demonstrate a light processing technology that can overcome this obstacle successfully, by enabling the full-coverage, pure-phase CsPbIBr2 films featured with large grains, high crystallinity, and preferential [100] grains orientation, along with favorable electronic structure. It is achieved by the exposure of CsPbIBr2 precursor film formed in a conventional one-step spin-coating route to a simulated AM 1.5 G illumination before thermal annealing. The resulting carbon-based, all-inorganic planar cells give an optimized power conversion efficiency (PCE) of 8.60% with the V-oc of 1.283 V. Notably, such an impressive V-oc stands the highest value among all of the previously reported CsPbIBr2 solar cells; hence, its PCE exceeds nearly all of them. Therefore, our work suggests a new route to further improve the efficiency of low-cost, stable, and simple-fabrication CsPbIBr2 solar cells.