Owing to inevitable thermal/moisture instability for organic-inorganic hybrid perovskites, pure inorganic perovskite cesium lead halides with both inherent stability and prominent photovoltaic performance have become research hotspots as a promising candidate for commercial perovskite solar cells. However, it is still a serious challenge to synthesize desired cubic cesium lead iodides (CsPbI 3 ) with superior photovoltaic performance for its thermodynamically metastable characteristics. Herein, polymer poly-vinylpyrrolidone (PVP)-induced surface passivation engineering is reported to synthesize extra-long-term stable cubic CsPbI 3 . It is revealed that acylamino groups of PVP induce electron cloud density enhancement on the surface of CsPbI 3 , thus lowering surface energy, conducive to stabilize cubic CsPbI 3 even in micrometer scale. The cubic-CsPbI 3 PSCs exhibit extra-long carrier diffusion length (over 1.5 μm), highest power conversion efficiency of 10.74% and excellent thermal/moisture stability. This result provides important progress towards understanding of phase stability in realization of large-scale preparations of efficient and stable inorganic PSCs.

Since the first introduction of the organic-inorganic hybrid perovskite in the field of optoelectronics, extraordinary progress in both photoelectric-conversion-efficiency and stability of perovskite solar cells (PSCs) have been witnessed. However,...

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.

Atomically thin 2D carbon nitride sheets (CNS) are promising materials for photocatalytic applications due to their large surface area and very short charge‐carrier diffusion distance from the bulk to the surface. However, compared to their bulk counterpart, CNS' applications always suffer from an enlarged bandgap and thus narrowed solar absorption range. Here, an approach to significantly increase solar absorption of the atomically thin CNS via fluorination followed by thermal defluorination is reported. This approach can greatly increase the visible‐light absorption of CNS by extending the absorption edge up to 578 nm. The modulated CNS loaded with Pt cocatalyst as a photocatalyst shows a superior photocatalytic hydrogen production activity under visible‐light irradiation to Pt‐CNS. Combining experimental characterization with theoretical calculations shows that this approach can introduce cyano groups into the framework of CNS as well as the accompanied nitrogen vacancies at the edges, which leads to both narrowing the bandgap and changing the charge distribution. This study will provide an effective strategy to increase solar absorption of carbon‐nitride‐based photocatalysts for solar energy conversion applications.

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.

Two‐dimensional (2D) hybrid perovskites have shown many attractive properties associated with their soft lattices and multiple quantum well structure. Herein, we report the synthesis and characterization of two new multifunctional 2D hybrid perovskites, (PED)CuCl4 and (BED)2CuCl6, which show reversible thermochromic behavior, dramatic temperature‐dependent conductivity change, and strong ferromagnetism. Upon temperature change, the (PED)CuCl4 and (BED)2CuCl6 crystals exhibit a reversible color change between yellow and red‐brown. The associated structural changes were monitored by in situ temperature‐dependent powder X‐ray diffraction (PXRD). The (BED)2CuCl6 exhibits superior thermal stability, with a thermochromic working temperature up to 443 K. The conductivity of (BED)2CuCl6 changes over six orders of magnitude upon temperature change. The 2D perovskites exhibit ferromagnetic properties with Curie temperatures around 13 K.

Graphene quantum dots with the high edge-to-area ratio have possibly substantial spin polarized edge states, which theoretically can generate fascinating magnetic properties. The magnetism of well-defined graphene quantum dots is relevant with both fundamental physics and potential applications in spintronics. In this article, we report the intrinsic magnetism of graphene quantum dots. Our graphene quantum dots with the average diameter of ca. 2.04 nm show the purely Curie-like paramagnetism with the local moment of 1.2 μ B at 2 K. It is proposed that the magnetic moment of graphene quantum dots may mainly origin from the residual zigzag edges passivated by hydroxyl groups. The ratio of nonmagnetic graphene quantum dots is approximately 6/7, with most of the magnetic edge states suppressed by edge defects and/or edge reconstruction arising from the high-temperature annealing. Our study experimentally unveils the intrinsic magnetism of graphene quantum dots.