Metal halide perovskites of the general formula ABX 3 -where A is a monovalent cation such as caesium, methylammonium or formamidinium; B is divalent lead, tin or germanium; and X is a halide anion-have shown great potential as light harvesters for thin-film photovoltaics [1][2][3][4][5] . Among a large number of compositions investigated, the cubic α-phase of formamidinium lead triiodide (FAPbI 3 ) has emerged as the most promising semiconductor for highly efficient and stable perovskite solar cells [6][7][8][9] , and maximizing the performance of this material in such devices is of vital importance for the perovskite research community. Here we introduce an anion engineering concept that uses the pseudo-halide anion formate (HCOO − ) to suppress anion-vacancy defects that are present at grain boundaries and at the surface of the perovskite films and to augment the crystallinity of the films. The resulting solar cell devices attain a power conversion efficiency of 25.6 per cent (certified 25.2 per cent), have long-term operational stability (450 hours) and show intense electroluminescence with external quantum efficiencies of more than 10 per cent. Our findings provide a direct route to eliminate the most abundant and deleterious lattice defects present in metal halide perovskites, providing a facile access to solution-processable films with improved optoelectronic performance.Perovskite solar cells (PSCs) have attracted much attention since their first demonstration in 2009 [1][2][3][4][5] . The rapid expansion of research into PSCs has been driven by their low-cost solution processing and attractive optoelectronic properties, including a tunable bandgap 6 , high absorption coefficient 10 , low recombination rate 11 and high mobility of charge carriers 12 . Within a decade, the power conversion efficiency (PCE) of single-junction PSCs progressed from 3% to a certified value of 25.5% 13 , the highest value obtained for thin-film photovoltaics. Moreover, through the use of additive and interface engineering strategies, the long-term operational stability of PSCs now exceeds 1,000 hours in full sunlight 14,15 . PSCs therefore show great promise for deployment as the next generation of photovoltaics.Compositional engineering plays a key part in achieving highly efficient and stable PSCs. In particular, mixtures of methylammonium lead triiodide (MAPbI 3 ) with formamidinium lead triiodide (FAPbI 3 ) have been extensively studied 5,7 . Compared to MAPbI 3 , FAPbI 3 is thermally more stable and has a bandgap closer to the Shockley-Queisser limit 6 , rendering FAPbI 3 the most attractive perovskite layer for single-junction PSCs.Unfortunately, thin FAPbI 3 films undergo a phase transition from the black α-phase to a photoinactive yellow δ-phase below a temperature of 150 °C. Previous approaches to overcome this problem have included mixing FAPbI 3 with a combination of methylammonium (MA + ), caesium (Cs + ) and bromide (Br − ) ions; however, this comes at the cost of blue-shifted absorbance and phase segregation under...

To date, the light emitting diode (LED) based halide perovskite was rapidly developed due to the outstanding property of perovskite materials. However, the blue perovskite LEDs based on the bulk halide perovskites have been rarely researched and showed low efficiencies. The bulk blue perovskite LEDs suffered from insufficient coverage on the substrate due to the low solubility of the inorganic Cl sources or damaged by the structural instability with participation of organic cations. Here, we show the new method of fabricating stable inorganic bulk blue perovskite LEDs with the anion exchange approach to avoid use of insoluble Cl precursors. The devices showed nice operational spectral stability at the desired blue emission peak. The bulk perovskite blue LEDs showed a maximum luminance of 1468 and 494 cd m −2 for the 490 and 470 nm emission peaks, respectively.

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Over a short period of approximately 10 years, metal‐halide‐perovskite‐based photovoltaics have demonstrated unprecedented improvements in solar cell performance beyond the various major photovoltaic semiconductor materials such as organic, cadmium telluride, and copper indium gallium selenide. With this, the current focus lies on the commercialization of perovskite solar cell technology and the issues encountered while ensuring and balancing high efficiency, stability, and eco‐friendliness in the photovoltaic community. This article reviews prominent developments in perovskite‐based photovoltaic power generation based on the ABI3 structure, describing the current state and understanding of state‐of‐the‐art solar cell drives. Accordingly, methods to improve the efficiency and long‐term operational stability, lead toxicity, nonlead perovskites, bandgap optimization, and tandem solar cells are discussed. Prospects and views on future research considering the feasibility of perovskite technology commercialization are provided.

Quasi-two-dimensional (2D) perovskites have recently emerged as emitters in blue perovskite light-emitting diodes (PeLEDs). The cascading energy-transfer process between different 2D phases plays an essential role in the high performance of this class of PeLEDs. Herein, we propose an interfacial engineering strategy by incorporating a zwitterionic additive, l-phenylalanine, into the hole-injection layer (HIL), enabling suppression of trap-assisted deactivation channels by virtue of the coordination interactions between the additive and Pb2+ defects in the perovskite phase. In addition, the introduction of l-phenylalanine reduces the release of metallic indium species from indium tin oxide substrates initiated by acidic HILs, resulting in the suppression of luminescence quenching in the perovskite layer. The synergetic benefits create an ideal energy landscape, blocking energy losses and boosting PeLED performance with a peak external quantum efficiency of 10.98% at 480 nm and extended device lifetimes. Our approach provides a versatile strategy to achieve high-performance blue PeLEDs.