The optoelectronic properties of perovskite films are closely related to the film quality, so depositing dense, uniform, and stable perovskite films is crucial for fabricating high-performance perovskite solar cells (PSCs). CsPbI 2 Br perovskite, prized for its superb stability toward light soaking and thermal aging, has received a great deal of attention recently. However, the air instability and poor performance of CsPbI 2 Br PSCs are hindering its further progress. Here, an approach is reported for depositing high-quality CsPbI 2 Br films via the Lewis base adducts PbI 2 (DMSO) and PbBr 2 (DMSO) as precursors to slow the crystallization of the perovskite film. This process produces CsPbI 2 Br films with large-scale crystalline grains, flat surfaces, low defects, and long carrier lifetimes. More interestingly, PbI 2 (DMSO) and PbBr 2 (DMSO) adducts could significantly improve the stability of CsPbI 2 Br films in air. Using films prepared by this technique, a power conversion efficiency (PCE) of 14.78% is obtained in CsPbI 2 Br PSCs, which is the highest PCE value reported for CsPbI 2 Br-based PSCs to date. In addition, the PSCs based on DMSO adducts show an extended operational lifetime in air. These excellent performances indicate that preparing high-quality inorganic perovskite films by using DMSO adducts will be a potential method for improving the performance of other inorganic PSCs.

The conduction band energy, conductivity, mobility, and electronic trap states of electron transport layer (ETL) are very important to the efficiency and stability of a planar perovskite solar cell (PSC). However, as the most widely used ETL, TiO often needs to be prepared under high temperature and has unfavorable electrical properties such as low conductivity and high electronic trap states. Modifications such as elemental doping are effective methods for improving the electrical properties of TiO and the performance of PSCs. In this study, Nb-doped TiO films are prepared by a facile one-port chemical bath process at low temperature (70 °C) and applied as a high quality ETL for planar PSCs. Compared with pure TiO, the Nb-doped TiO is more efficient for photogenerated electron injection and extraction, showing higher conductivity, higher mobility, and lower trap-state density. A PSC with 1% Nb-doped TiO yielded a power conversion efficiency of more than 19%, with about 90% of its initial efficiency remaining after storing for 1200 h in air or annealing at 80 °C for 20 h in a glovebox.

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All‐inorganic CsPbX3‐based perovskites, such as CsPbI2Br, show much better thermal and illumination stability than their organic–inorganic hybrid counterparts. However, fabrication of high‐quality CsPbI2Br perovskite film normally requires annealing at a high temperature (>250 °C) that is not compatible with the plastic substrate. In this work, a Lewis base adduct‐promoted growth process that makes it possible to fabricate high quality CsPbI2Br perovskite films at low temperature is promoted. The mechanism is attributed to synthesized dimethyl sulfoxide (DMSO) adducts which allow a low activation energy route to form CsPbI2Br perovskite films during the thermal annealing treatment. A power conversion efficiency (PCE) of 13.54% is achieved. As far as it is known, this is the highest efficiency for the CsPbI2Br solar cells fabricated at low temperature (120 °C). In addition, the method enables fabrication of flexible CsPbI2Br PSCs with PCE as high as 11.73%. Surprisingly, the bare devices without any encapsulation maintain 70% of their original PCEs after being stored in ambient air for 700 h. This work provides an approach for preparing other high performance CsPbX3‐based perovskite solar cells (PSCs) at low temperature, particularly for flexible ones.

In this paper, it is demonstrated that two-dimensional TiS2 nanosheets can be applied as an effective ETL in planar PSCs for the first time.