Tin (Sn)-based and mixed tin−lead (Sn−Pb) perovskites have attracted increased attention as promising candidates for new generation lead-free perovskite and all-perovskite tandem solar cells. However, as an inevitably critical issue, Sn(II) induced serious defects and oxidation and caused poor photovoltaic performance and unsatisfactory stability for Sn-based and mixed Sn−Pb perovskites. Herein, a comprehensive understanding on defect classification, defect formation, defect effect on performance, and defect passivation strategies is reviewed on the Sn(II) induced defects. The Sn(II)-based defects can be classified from the aspects of defect dimensions and shallow/deep levels in energy structure according to three main origins, i.e. low defect tolerance, oxidation, and fast crystallization. Then, the state-of-the-art defect passivation strategies including surface Lewis acid/base coordination, low/mixed dimensional perovskite design, composition regulation and crystal orientation modulation, and reducing agent assistance are summarized systematically. Lastly, several key scientific issues and future research prospectives are proposed for achieving stable and high-performance Sn-related perovskite photovoltaics.

Despite remarkable progress in hybrid perovskite solar cells (PSCs), the concern of toxic lead ions remains a major hurdle in the path towards PSC's commercialization; tin (Sn)‐based PSCs outperform the reported Pb‐free perovskites in terms of photovoltaic performance. However, it is of a particularly great challenge to develop effective passivation strategies to suppress Sn(II) induced defect densities and oxidation for attaining high‐performance all‐inorganic CsSnI3 PSCs. Herein, a facile yet effective thioamides passivation strategy to modulate defect state density at surfaces and grain boundaries in CsSnI3 perovskites is reported. The thiosemicarbazide (TSC) with SCN functional groups can make strong coordination interaction with charge defects, leading to enhanced electron cloud density around defects and increased vacancy formation energies. Importantly, the surface passivation can reduce the deep level trap state defect density originated from undercoordinated Sn2+ ion and Sn2+ oxidation, significantly restraining nonradiative recombination and elongating the carrier lifetime of TSC treated CsSnI3 PSCs. The surface passivated all‐inorganic CsSnI3 PSCs based on an inverted configuration delivers a champion power conversion efficiency (PCE) of 8.20%, with a prolonged lifetime over 90% of initial PCE, after 500 h of continuous illumination. The present strategy sheds light on surface defect passivation for achieving highly efficient all‐inorganic lead‐free Sn‐based PSCs.

High-efficiency and low-cost perovskite solar cells (PSCs) are desirable candidates for addressing the scalability challenge of renewable solar energy.

Despite Sn‐based perovskite solar cells (PSCs) prevailing over lead‐free candidates, the Sn vacancies (VSn) and Sn4+ defects seriously deteriorate device photovoltaic performance. The presently reported methods can only effectively achieve surface defect passivation, and it is of great challenge and fundamental importance to develop efficient strategy to deal with the intrinsic defects located inside the lattice. Herein, a novel bulk defect suppression strategy is proposed, introducing large organic piperazine cations (PZ2+) into the lattice of 3D FASnI3 perovskite to restrain the generation of bulk defects. The incorporation of PZ2+ results in forming a FA1−2yPZ2ySn1−yI3 (0 ≤ y ≤ 0.25) structure with no reduction in dimensionality, which guarantees the continuity of [SnI6] octahedral structures with unobstructed carrier transport and reduced charged defects. The potent interactions between PZ2+ and [SnI6] structures enhance VSn formation energy and effectively suppress bulk defect formation. As a result, the FASnI3+1%PZ films exhibit optimized crystalline quality, decreased background carrier density, lower p‐type self‐doping, and reduced trap state density. Benefiting from the above advantages, the FASnI3+1%PZ device achieves an optimal PCE of 9.15% and unencapsulated device maintains over 95% of initial PCE after aging for 1000 h in N2 golvebox. The bulk defect suppression strategy provides fire‐new building bricks toward high‐performance Sn‐based PSCs.

Open-circuit voltage loss and instability from surface Sn(II) oxidation and high-density Sn vacancies pose great hurdles for developing highperformance Sn-based perovskite solar cells (PSCs). Turning attention from the bulk microstructure to surface reconstruction is promising to push the performance enhancement of Sn-based PSCs. Herein, a surface-modulation strategy based on 6-maleimidohexanehydrazide trifluoroacetate is rationally designed to reconstruct the surface structure of FASnI 3 films to manage the Fermi level and passivate defects. The electronic state evolution results in an n-type Fermi level shift of the shallow surface, thereby forming an extra back-surface field for electron extraction. Meanwhile, the ion-pairing agent affords passivating cationic and anionic defects, thereby nullifying the charged-defect-rich surface. In particular, the reductive hydrazide group and carboxyl groups alleviate superficial Sn(IV) and inhibit Sn(IV) formation, homogenizing surface potential and prolonging carrier lifetime. Accordingly, devices deliver a champion power conversion efficiency (PCE) of 13.64% and an elongated lifespan, with over 75% of the original PCE after 1000 h of illumination (O 2 < 50 ppm). This work presents a new insight on the surface reconstruction strategy for developing high-performance Sn-based PSCs.