In this work, a fully tin‐based, mixed‐organic‐cation perovskite absorber (FA)x(MA)1− xSnI3 (FA = NH2CH = NH2 +, MA = CH3NH3 +) for lead‐free perovskite solar cells (PSCs) with inverted structure is presented. By optimizing the ratio of FA and MA cations, a maximum power conversion efficiency of 8.12% is achieved for the (FA)0.75(MA)0.25SnI3‐based device along with a high open‐circuit voltage of 0.61 V, which originates from improved perovskite film morphology and inhibits recombination process in the device. The cation‐mixing approach proves to be a facile method for the efficiency enhancement of tin‐based PSCs.

It is extremely significant to study the trap state passivation and minimize the trap states of perovskite to achieve high-performance perovskite solar cells (PSCs). Here, we have first revealed and demonstrated that a novel p-type conductor Cu(thiourea)I [Cu(Tu)I] incorporated in perovskite layer can effectively passivate the trap states of perovskite via interacting with the under-coordinated metal cations and halide anions at the perovskite crystal surface. The trap state energy level of perovskite can be shallowed from 0.35-0.45 eV to 0.25-0.35 eV. In addition, the incorporated Cu(Tu)I can participate in constructing the p-i bulk heterojunctions with perovskite, leading to an increase of the depletion width from 126 to 265 nm, which is advantageous for accelerating hole transport and reducing charge carrier recombination. For these two synergistic effects, Cu(Tu)I can play a much better role than that of the traditional p-type conductor CuI, probably due to its identical valence band maximum with that of perovskite, which enables to not only lower the trap state energy level to a greater extent but also eliminate the potential wells for holes at the p-i heterojunctions. After optimization, a breakthrough efficiency of 19.9% has been obtained in the inverted PSCs with Cu(Tu)I as the trap state passivator of perovskite.

Lead (Pb)‐free tin (Sn)‐based perovskite solar cells (PSCs) have been recognized as one of the solutions to the toxicity of Pb and drawn considerable attention. However, Sn4+ caused by oxidation or incomplete reduction during synthesis severely deteriorates the device performance. Herein, the authors firstly reveal that the addition of Sn powder into the FASnI3 (FANH2CHNH2+) precursor solution prepared from SnI2 with 99% purity leads to great improvement of the device performance with a maximum power conversion efficiency (PCE) of 6.75%, which is, to the best of their knowledge, the highest efficiency among those of the FASnI3‐based PSCs with SnF2 as the only additive, comparable to and even higher than the device fabricated from SnI2 with a high purity of 99.999%.