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...

Improvements to perovskite solar cells (PSCs) have focused on increasing their power conversion efficiency (PCE) and operational stability and maintaining high performance upon scale-up to module sizes. We report that replacing the commonly used mesoporous–titanium dioxide electron transport layer (ETL) with a thin layer of polyacrylic acid–stabilized tin(IV) oxide quantum dots (paa-QD-SnO 2 ) on the compact–titanium dioxide enhanced light capture and largely suppressed nonradiative recombination at the ETL–perovskite interface. The use of paa-QD-SnO 2 as electron-selective contact enabled PSCs (0.08 square centimeters) with a PCE of 25.7% (certified 25.4%) and high operational stability and facilitated the scale-up of the PSCs to larger areas. PCEs of 23.3, 21.7, and 20.6% were achieved for PSCs with active areas of 1, 20, and 64 square centimeters, respectively.

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A self-organized hole extraction layer (SOHEL) with high work function (WF) is designed for energy level alignment with the ionization potential level of CH3 NH3 PbI3 . The SOHEL increases the built-in potential, photocurrent, and power conversion efficiency (PCE) of CH3 NH3 PbI3 perovskite solar cells. Thus, interface engineering of the positive electrode of solution-processed planar heterojunction solar cells using a high-WF SOHEL is a very effective way to achieve high device efficiency (PCE = 11.7% on glass).

Organic–inorganic hybrid perovskite materials offer the potential for realization of low-cost and flexible next-generation solar cells fabricated by low-temperature solution processing. Although efficiencies of perovskite solar cells have dramatically improved up to 19% within the past 5 years, there is still considerable room for further improvement in device efficiency and stability through development of novel materials and device architectures. Here we demonstrate that inverted-type perovskite solar cells with pH-neutral and low-temperature solution-processable conjugated polyelectrolyte as the hole transport layer (instead of acidic PEDOT:PSS) exhibit a device efficiency of over 12% and improved device stability in air. As an alternative to PEDOT:PSS, this work is the first report on the use of an organic hole transport material that enables the formation of uniform perovskite films with complete surface coverage and the demonstration of efficient, stable perovskite/fullerene planar heterojunction solar cells.

made their great discovery of electromagnetic induction, there have been continuous developments in electrical power generation. Most people today get electricity from thermal, hydroelectric, or nuclear power generation systems, which use this electromagnetic induction phenomenon. Here we propose a new method for electrical power generation, without using electromagnetic induction, by mechanically modulating the electrical double layers at the interfacial areas of a water bridge between two conducting plates. We find that when the height of the water bridge is mechanically modulated, the electrical double layer capacitors formed on the two interfacial areas are continuously charged and discharged at different phases from each other, thus generating an AC electric current across the plates. We use a resistor-capacitor circuit model to explain the results of this experiment. This observation could be useful for constructing a micro-fluidic power generation system in the near future.

We investigate mixed solvents of N,N-dimethylformamide (DMF) and γ-butyrolactone (GBL) to produce the smooth surface of a perovskite film and uniform crystal domains. This ideal morphology from mixed solvents enhances the power conversion efficiency to over 6% by improving the exciton dissociation efficiency and reducing the recombination loss at both interfaces of PEDOT:PSS/perovskite and perovskite/PCBM.

MQDs-SnO2-modulated perovskite crystallization processes visualized by in situ 2D GIXRD technique.