The toxicity of lead perovskite hampers the commercialization of perovskite-based photovoltaics. While tin perovskite is a promising alternative, the facile oxidation of tin(II) to tin(IV) causes a high density of defects, resulting in lower solar cell efficiencies. Here, we show that tin(0) nanoparticles in the precursor solution can scavenge tin(IV) impurities, and demonstrate that this treatment leads to effectively tin(IV)-free perovskite films with strong photoluminescence and prolonged decay lifetimes. These nanoparticles are generated by the selective reaction of a dihydropyrazine derivative with the tin(II) fluoride additive already present in the precursor solution. Using this nanoparticle treatment, the power conversion efficiency of tin-based solar cells reaches 11.5%, with an open-circuit voltage of 0.76 V. Our nanoparticle treatment is a simple and broadly effective method that improves the purity and electrical performance of tin perovskite films.

Recently, foldable electronics technology has become the focus of both academic and industrial research. The foldable device technology is distinct from flexible technology, as foldable devices have to withstand severe mechanical stresses such as those caused by an extremely small bending radius of 0.5 mm. To realize foldable devices, transparent conductors must exhibit outstanding mechanical resilience, for which they must be micrometer‐thin, and the conducting material must be embedded into a substrate. Here, single‐walled carbon nanotubes (CNTs)–polyimide (PI) composite film with a thickness of 7 µm is synthesized and used as a foldable transparent conductor in perovskite solar cells (PSCs). During the high‐temperature curing of the CNTs‐embedded PI conductor, the CNTs are stably and strongly p‐doped using MoOx, resulting in enhanced conductivity and hole transportability. The ultrathin foldable transparent conductor exhibits a sheet resistance of 82 Ω sq.−1 and transmittance of 80% at 700 nm, with a maximum‐power‐point‐tracking‐output of 15.2% when made into a foldable solar cell. The foldable solar cells can withstand more than 10 000 folding cycles with a folding radius of 0.5 mm. Such mechanically resilient PSCs are unprecedented; further, they exhibit the best performance among the carbon‐nanotube‐transparent‐electrode‐based flexible solar cells.

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Polymers or polymeric materials are used as additives for promoting the nucleation and crystallization of perovskite films to increase the crystal grain size. Due to their high molecular weight, polymers remain within perovskite‐crystal grain boundaries (GBs), where they passivate trap sites. Furthermore, some polymers function as charge‐transport materials in interfacial layers to effectively separate charge carriers and reduce charge recombination. Certain hydrophobic polymers protect perovskite films against moisture, whereas elastic polymers contribute to the mechanical resilience of perovskite films by crosslinking and self‐healing. Although polymeric additives have become essential to perovskite fabrication, a thorough review has not summarized their application to perovskite solar cells. Therefore, various strategies are comprehensively discussed for incorporating typical polymers and 1D polymeric materials into perovskite materials to improve the efficiency and stability of perovskite devices. Herein, thermoplastic, hydrophilic, and conductive polymers and elastomers are focused and related works are chronologically discussed to clearly elucidate the advances in perovskite devices.

Lead (Pb) halide perovskites have attracted significant attention in the field of optoelectronics. However, due to the disadvantages associated with the presence of Pb in perovskite, its use should be minimized, if not completely eliminated. Herein, an efficient Pb‐free Sn‐based halide perovskite photodetector (PD) that is sensitive to visible and near‐infrared light is developed. The Sn perovskite is characterized with low toxicity and a narrow bandgap, and exhibits lower shunt leakage and a higher built‐in potential compared with a Pb‐based perovskite. Also, the relatively stronger bond strength between Sn and iodine ions in comparison with that observed in the Pb‐based perovskite effectively prevents charge injections that are vulnerable to dark current suppression. The Sn‐based perovskite PD demonstrates a high signal‐to‐noise ratio (SNR) of 51.12 dB, as well as an excellent cut‐off frequency of 763 kHz. To the best knowledge, this device is one of the fastest and most efficient photodiode‐type Sn‐based perovskite PDs developed to date. Unlike the Pb‐based perovskite device, the Sn‐based perovskite PD retains its high SNR over time. This effect may be attributed to the low movement of ion vacancies and degree of vertical shunt leakage in the perovskite material.