Contemporary thin-film photovoltaic (PV) materials contain elements that are scarce (CIGS) or regulated (CdTe and lead-based perovskites), a fact that may limit the widespread impact of these emerging PV technologies. Tin halide perovskites utilize materials less stringently regulated than the lead (Pb) employed in mainstream perovskite solar cells; however, even today’s best tin-halide perovskite thin films suffer from limited carrier diffusion length and poor film morphology. We devised a synthetic route to enable in situ reaction between metallic Sn and I2 in dimethyl sulfoxide (DMSO), a reaction that generates a highly coordinated SnI2·(DMSO) x adduct that is well-dispersed in the precursor solution. The adduct directs out-of-plane crystal orientation and achieves a more homogeneous structure in polycrystalline perovskite thin films. This approach improves the electron diffusion length of tin-halide perovskite to 290 ± 20 nm compared to 210 ± 20 nm in reference films. We fabricate tin-halide perovskite solar cells with a power conversion efficiency of 14.6% as certified in an independent lab. This represents a ∼20% increase compared to the previous best-performing certified tin-halide perovskite solar cells. The cells outperform prior earth-abundant and heavy-metal-free inorganic-active-layer-based thin-film solar cells such as those based on amorphous silicon, Cu2ZnSn­(S/Se)4 , and Sb2(S/Se)3.

Conspectus Perovskite semiconductors are regarded as next-generation photovoltaic materials owing to their superb optoelectronic properties, including an excellent carrier diffusion length, strong light absorbption, low defect density, and solution processability. The PCE of lead perovskite solar cells (LPSC) rapidly increased from 3.8 to 25.5% in the past decade. However, the inclusion of soluble, toxic lead shadows its application due to environmental concerns. Furthermore, on the basis of the Shockley–Quisser (S–Q) limit, the efficiency of lead perovskite is limited to 32% since its band gap is >1.5 eV. To increase the efficiency of perovskite solar cells further, perovskite materials with a smaller band gap are required. Tin halide perovskite is currently the most promising alternative candidate that can address the above challenges due to its potentially less toxic character and electronic configuration analogous to that of lead. Its band gap (sub-1.4 eV) is lower than that of lead perovskite, approaching the ideal band gap with a theoretical efficiency of up to 33.4% based on the S–Q equation. However, tin perovskite is extremely easy to oxidize due to its unique electronic structure. Early works focus on the development of methods to reduce tin oxidation such as the addition of antioxidant additives or using low-dimensional structures. On the basis of these strategies, the reproducibility and efficiency of TPSCs have been significantly improved. In recent years, many works including composition engineering, functional additives, and device structure engineering have been used to improve the performance of TPSCs. On the basis of these strategies, the open-circuit voltage is improved to 0.94 V and the PCE certified by an independent laboratory is up to 12.4%. Meanwhile, the stability of TPSCs is significantly improved, and the stabilized power output time is up to 1000 h. Therefore, tin perovskite is emerging as a new generation of low-cost thin-film photovoltaic technology. This Account summarizes the properties of tin halide perovskites and the material and device engineering strategies toward more efficient and stable TPSCs. We highlight the unique properties of tin perovskites that distinguish them from lead perovskites, including their electronic structure, band structure, chemical properties, and so on. We discuss the critical challenges for the further development of TPSCs such as oxidation, high background carriers, uncontrollable crystallization, interface recombination, band alignment, and instability. In the end, we introduce potential directions for the future development of TPSCs including probing the formation mechanisms of tin perovskite, revealing the basic properties of Sn perovskite, overcoming the stability issue of TPSCs, and understanding TPSC device physics and structure engineering.

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The manipulation of the dimensionality and nanostructures based on the precise control of the crystal growth kinetics boosts the flourishing development of perovskite optoelectronic materials and devices. Herein, a low‐dimensional inorganic tin halide perovskite, CsSnBrI2−x(SCN)x, with a mixed 2D and 3D structure is fabricated. A kinetic study indicates that Sn(SCN)2 and phenylethylamine hydroiodate can form a 2D perovskite structure that acts as a template for the growth of the 3D perovskite CsSnBrI2−x(SCN)x. The film shows an out‐of‐plane orientation and a large grain size, giving rise to reduced defect density, superior thermostability, and oxidation resistance. A solar cell based on this low‐dimensional film reaches a power conversion efficiency of 5.01 %, which is the highest value for CsSnBrxI3−x perovskite solar cells. Furthermore, the device shows enhanced stability in ambient air.

Li-rich cathode materials possess a much higher theoretical energy density than all intercalated cathode materials currently reported and thus are considered as the most promising candidate for next-generation high-energy density Li-ion batteries. However, the rapid voltage decay and the irreversible phase transition of O3-type Li-rich cathode materials often lessen their actual energy density and limit their practical applications, and thus, effectively suppressing the voltage decay of Li-rich cathodes becomes the hotspot of the current research. Herein, the F-doped O2-type Li-rich cathode materials Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O 2+δ−x F x (F-O2-LRO) are designed and prepared based on the P2-type sodium-ion cathode materials Na 5/6 Li 1/4 (Mn 0.54 Ni 0.13 Co 0.13 ) 3/4 -O 2+δ (Na-LRO) by ion exchange. It has been found that the asprepared F-O2-LRO exhibits excellent electrochemical performance, for example, a high discharge specific capacity of 280 mA h g −1 at 0.1 C with an initial Coulombic efficiency of 94.4%, which is obviously higher than the original LRO (77.2%). After 100 cycles, the F-O2-LRO cathode can still maintain a high capacity retention of 95% at a rate of 1 C, while the capacity retention of the original LRO is only 69.1% at the same current rate. Furthermore, the voltage difference (ΔV) of F-O2-LRO before and after cycling is only 0.268 V after 100 cycles at 1 C, which is less than that of the LRO cathode (0.681 V), indicating much lower polarization. Besides, even at a high current rate of 5 C, F-O2-LRO still displays a satisfactory discharge capacity of 210 mA h g −1 with a capacity retention of 90.1% after 100 cycles. Therefore, this work put forward a new strategy for the development and industrial application of Li-rich cathode materials in high-energy Li-ion batteries.