Hybrid organic-inorganic halide perovskites with the prototype material of CH 3 NH 3 PbI 3 have recently attracted intense interest as low-cost and high-performance photovoltaic absorbers. Despite the high power conversion efficiency exceeding 20% achieved by their solar cells, two key issues -the poor device stabilities associated with their intrinsic material instability and the toxicity due to water soluble Pb 2+ -need to be resolved before large-scale commercialization. Here, we address these issues by exploiting the strategy of cation-transmutation to design stable inorganic Pb-free halide perovskites for solar cells. The idea is to convert two divalent Pb 2+ ions into one monovalent M + and one trivalent M 3+ ions, forming a rich class of quaternary halides in double-perovskite structure. We find through first-principles calculations this class of materials have good phase stability against decomposition and wide-range tunable optoelectronic properties. With photovoltaic-functionality-directed materials screening, we identify eleven optimal materials with intrinsic thermodynamic stability, suitable band gaps, small carrier effective masses, and low excitons binding energies as promising candidates to replace Pb-based photovoltaic absorbers in perovskite solar cells. The chemical trends of phase stabilities and electronic properties are also established for this class of materials, offering useful guidance for the development of perovskite solar cells fabricated with them.

The material class of hybrid organic-inorganic perovskites has risen rapidly from a virtually unknown material in photovoltaic applications a short 7 years ago into a ∼ 20% efficient thin-film solar cell material. As promising as this class of materials is, however, there are limitations associated with its poor long-term stability, non-optimal band gap, presence of environmentally-toxic Pb element, etc. We herein apply a functionality-directed theoretical materials selection approach as a filter for initial screening of the compounds that satisfy the desired intrinsic photovoltaic functionalities and might overcome the above limitations. First-principles calculations are employed to systemically study thermodynamic stability and photovoltaic-related properties of hundred of candidate hybrid perovskites. We have identified in this materials selection process fourteen Ge and Sn-based materials with potential superior bulk-material-intrinsic photovoltaic performance. A distinct class of compounds containing NH3COH+ with the organic molecule derived states intriguingly emerging at band-edges is found. Comparison of various candidate materials offers insights on how composition variation and microscopic structural changes affect key photovoltaic relevant properties in this family of materials.

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Solar‐cell materials with a tetrahedral diamond structure and its derived structures (i.e., zinc blende and chalcopyrite) are the most successful family of materials, with power conversion efficiencies exceeding 20%. Recent breakthroughs based on lead halide perovskites have inspired intensive research on low‐cost photovoltaics beyond diamond‐structured materials. While research has focused on addressing the key challenges faced by lead halide perovskites, that is, the stability and toxicity issues, it is of greater interest to develop perovskites into a new family of solar‐cell materials. Here, the recent efforts toward this goal are reviewed. The focus is on computational materials design, including single, double, 2D, and nonhalide perovskites and perovskite‐like materials. Meanwhile, related experiments are also reviewed with a hope that such this will help identify potential issues as well as enlightening ideas to achieve further computation‐driven materials discovery.

Large-scale Ag nanosheet-assembled micro-hemispheres, with sufficient hot spots on their surfaces, have been achieved on an indium tin oxide substrate via electrodeposition. Surface-enhanced Raman scattering (SERS) measurements demonstrate that the Ag nanosheet-assembled micro-hemispheres can serve as sensitive and reproducible SERS substrates.