SnO 2 is widely used and one of the most efficient electron transport layers in perovskite solar cells (PSCs). However, SnO 2 films often contain detrimental defects and may also have mismatches in energy level alignment with perovskite films, thus limiting the open-circuit voltage (V OC ). Managing the defects and band structure are critical to reduce energy loss in PSCs. Herein, cobalt chloride hexahydrate (CoCl 2 •6H 2 O) is introduced into a SnO 2 film, which shows favorable energy level alignment and better charge extraction. Correspondingly, an enhanced V OC up to 1.20 V was achieved along with an efficiency of 23.82%, which is the record open-circuit voltage at the optical band gap of 1.54 eV in planar structure PSCs. Moreover, the target devices show enhanced stability, which retains 83.5% of their initial efficiencies after 200 h under continuous irradiation. The doping method provides an effective strategy for reducing energy loss to further enhance the efficiency of PSCs.

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A two-step solution sequential deposition has been successfully applied to narrow-bandgap (below 1.60 eV) perovskite solar cells (PSCs), while it has not been widely used in wide-bandgap PSCs and monolithic tandem solar cells (TSCs). Here, a lead halide complex is formed by introducing a formamidinium iodide (FAI) and rubidium acetate (RbAc) into the first step. The results show that the lead halide complex alters the crystallization kinetics and promotes a prominent orientation (100) growth of the perovskite film, resulting in an efficiency of 27.64% for monolithic perovskite/silicon TSCs. Additionally, an enlarged-scaled tandem device with an efficiency of 22.81% (active area of 11.879 cm 2 ) is also achieved, which is one of the most efficient devices with an area greater than 10 cm 2 . This work provides an effective strategy to fabricate perovskite/silicon TSCs with high performance, reproducibility, and large area via the two-step solution method, which will accelerate the industrialization of perovskite/silicon tandem technique.