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Metal halide perovskites of the general formula ABX.sub.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.sup.1-5. Among a large number of compositions investigated, the cubic [alpha]-phase of formamidinium lead triiodide (FAPbI.sub.3) has emerged as the most promising semiconductor for highly efficient and stable perovskite solar cells.sup.6-9, 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.sup.-) 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. Incorporation of the pseudo-halide anion formate during the fabrication of [alpha]-FAPbI.sub.3 perovskite films eliminates deleterious iodide vacancies, yielding solar cell devices with a certified power conversion efficiency of 25.21 per cent and long-term operational stability., Author(s): Jaeki Jeong [sup.1] [sup.2] [sup.3] , Minjin Kim [sup.4] , Jongdeuk Seo [sup.1] , Haizhou Lu [sup.2] [sup.3] , Paramvir Ahlawat [sup.5] , Aditya Mishra [sup.6] , Yingguo Yang [...]

Surface passivation has been widely employed to suppress non‐radiative charge recombination and prevent interfacial charge accumulation in perovskite photovoltaics. In this report, carbazole modified with ammonium iodide connected via alkyl chains of different lengths (i.e., ethyl, butyl, and hexyl chains) is used to form passivation layers on formamidinium lead triiodide FAPbI3‐based perovskite films to improve operational stability. Owing to the strong hydrophobicity of the carbazole moiety, it is observed that the perovskite films with a carbazole passivation layer retain their initial properties even after direct contact with a water droplet for 100 s. In addition, carbazole treatment reduces the rate of trap‐assisted recombination at the surface and grain boundaries of the perovskite layer. Furthermore, it accelerates interfacial hole transfer from the perovskite to the charge transport layer. As a result, devices treated with carbazole hexylammonium iodide achieve a power conversion efficiency (PCE) of up to 24.3% during quasi‐steady‐state (QSS) measurements with extraordinary long‐term operational stability under conditions of the ISOS‐L‐1 protocol, maintaining 95% of their initial efficiency after 1000 h. [ABSTRACT FROM AUTHOR]

Pb‐free Sn‐based perovskite solar cells (PSCs) have significant potential for application in photovoltaic devices because of their suitable bandgap, low exciton binding energy, high carrier mobility, and long diffusion length. However, their performance is hampered by several issues. Sn‐based perovskites are highly susceptible to oxidation, which induces a high concentration of defects and degrades the chemical stability of the perovskite crystals. Herein, the anion formate (HCOO−) can effectively suppress the oxidation of Sn in the pure formamidinium tin triiodide (FASnI3) perovskite without using A‐site cationic additives. Moreover, the presence of formate results in a uniform pinhole‐free perovskite film with a low trap density, reduced charge carrier recombination, and improved charge extraction. Density functional theory calculations show that formate‐treated FASnI3 has improved stability against oxidative Sn degradation. The formate‐treated PSC achieves a power conversion efficiency of 12.11% at a high open‐circuit voltage of 0.71 V. The device exhibits improved stability in ambient air in which it maintained over 80% of its initial power conversion efficiency after 180 min because oxidation is inhibited owing to the strong interaction between Sn and formate. [ABSTRACT FROM AUTHOR]

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-SnO2) on the compact–titanium dioxide enhanced light capture and largely suppressed nonradiative recombination at the ETL–perovskite interface. The use of paa-QD-SnO2 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. [ABSTRACT FROM AUTHOR]

The pace of advancement and increasing power conversion efficiencies (PCEs) have provided the possibility for organic solar cells (OSCs) to be commercialized in a variety of applications, including semitransparent photovoltaics. The application of dielectric–metal–dielectric (DMD) transparent electrodes to OSCs is an effective way to achieve semitransparent OSCs with different colors. Herein, a DMD multilayer structure based on two Sb2O3 layers and silver (Ag) thin films as the top electrode is introduced. An ultrathin Sb2O3 layer is deposited between the electron transport layer and the Ag film as a bottom layer for the Sb2O3/Ag/Sb2O3 electrode; this layer inhibits Ag atom diffusion and aggregation, which leads to uniform formation of ultrathin Ag films. The thickness of the middle metal layer influences fill factor and short‐circuit current density values, which correlate well with device resistance and light reflection. For the top Sb2O3 layer, the thickness allows the selective transmittance of specific wavelengths of visible light while reflecting wavelengths that are not transmitted, creating a dichroic effect. OSCs are successfully fabricated using three kinds of colorful active layers in conjunction with Sb2O3/Ag/Sb2O3 electrodes, resulting in vividly colored devices with PCE of 6.33–7.88% and average visible transmittances of 23–30%. [ABSTRACT FROM AUTHOR]

We've observed intense fluorescence from the surface of lead formate crystals when they are precipitated from a CH3NH3PbBr3 (MAPbBr3) perovskite precursor solution. The crystals exhibit emission in the range of 500–550 nm with a photoluminescence quantum yield (PLQY) of up to 70%. The fluorescence is stable in water and at elevated temperature without significant decrease in PLQY for months, conditions which instantly decompose MAPbBr3. Fluorescence occurred with the highest quantum efficiency of 70% at an optimal 1 : 0.3 molar ratio of methylammonium formate and lead bromide and decreased rapidly for other ratios. Fluorescence was quenched using other halides (Cl or I) or other cations (Cs, ethylammonium, propylammonium, etc.). Single crystal analysis indicates that the material possesses the lead formate structure with lattice parameters which are identical to pristine lead formate, however, analysis of the particles by EDX, XPS and fluorescence microscopy confirms the presence of Br and fluorescence emission on the particle surfaces. The observed material characteristics indicate that the emissive species consists of a mixed-valence surface layer of Pb coordinated to both Br and formate ligands. [ABSTRACT FROM AUTHOR]

The all-inorganic perovskite CsPbI3 has emerged as an alternative photovoltaic material to organic–inorganic hybrid perovskites due to its non-volatile composition and comparable photovoltaic performance. However, its spontaneous deformation from the light-active black phase to a light-inactive yellow phase under ambient conditions, poor air stability, low thermal stability as well as high-temperature processing are challenging issues in the fabrication of CsPbI3-based solar cells. Herein, we introduce a new surface passivation strategy using camphor sulfonic acid (CSA) to improve the surface morphology and air stability of Ba-stabilized α-CsPbI3 perovskites at low temperature. The surface passivated, Ba-doped α-CsPbI3 was thermally stable upon annealing and highly photo-stable over a year, and it also exhibited a band gap of ∼1.72 eV, which is suitable for optoelectronic applications. The all-inorganic solar cell based on the Ba-doped α-CsPbI3 retained 98% of its initial PCE value even after 700 h, and red light-emitting diodes (LED) exhibited light emission at 700 nm with a bandwidth of 39 nm. To date, this is the first study on surface passivated, Ba-stabilized α-CsPbI3, which provides opportunities for the development of highly efficient tandem solar cells and other optoelectronic devices. [ABSTRACT FROM AUTHOR]

Lightweight and flexible photovoltaic devices have attracted great interest for specific potential applications, such as miniaturized drones, blimps, and aerospace electronics. This study aims to demonstrate ultralight and flexible perovskite solar cells (PSCs) with orthogonal silver nanowire (AgNW) transparent electrodes fabricated on 1.3 μm-thick polyethylene naphthalate foils. The smooth surface morphologies of the orthogonal AgNW transparent electrodes help prevent nonconducting silver halide formation generated by chemical reaction between the AgNWs and iodine in the active layer. The resultant PSCs with orthogonal AgNW transparent electrodes exhibit substantially improved device performance, achieving a power conversion efficiency (PCE) of 15.18%, over PSCs with random AgNW network electrodes (10.43% PCE). Moreover, ultralight and flexible PSCs with the orthogonal AgNW electrodes exhibit an excellent power-per-weight of 29.4 W g−1, which is the highest value reported for a lightweight solar cell device. These lightweight energy harvesting platforms can be further expanded for various wearable optoelectronic devices. [ABSTRACT FROM AUTHOR]

Processing for obtaining compact and uniform perovskite photoactive layers has been intensively studied over the last few years to achieve high power conversion efficiencies (PCEs) in solar cells. Particularly, high quality crystal growth of perovskite layers is critical to enhance device performance. We demonstrate an easy and effective new process for high efficiency p–i–n planar heterojunction structures of perovskite solar cells (PeSCs) by using a compact seed perovskite layer (CSPL). The CSPL assists vertical growth of perovskite crystals and obtains the highly crystalline perovskite photoactive layer, which leads to the reduction in the charge transfer resistance and a longer photoluminescence lifetime. The PeSC device with a CSPL shows a remarkably improved PCE, from 15.07% to 19.25%, with a record open circuit voltage (VOC) of 1.16 V in the p–i–n structure with pure crystal perovskite and negligible current density–voltage hysteresis. Additionally, a PCE of 20.37% was achieved in CSPL assisted n–i–p structure PeSCs. [ABSTRACT FROM AUTHOR]

Abstract: The development of solution‐processed field effect transistors (FETs) based on organic and hybrid materials over the past two decades has demonstrated the incredible potential in these technologies. However, solution processed FETs generally require impracticably high voltages to switch on and off, which precludes their application in low‐power devices and prevent their integration with standard logic circuitry. Here, a universal and environmentally benign solution‐processing method for the preparation of Ta2O5, HfO2 and ZrO2 amorphous dielectric thin films is demonstrated. High mobility CdS FETs are fabricated on such high‐κ dielectric substrates entirely via solution‐processing. The highest mobility, 2.97 cm2 V−1 s−1 is achieved in the device with Ta2O5 dielectric with a low threshold voltage of 1.00 V, which is higher than the mobility of the reference CdS FET with SiO2 dielectric with an order of magnitude decrease in threshold voltage as well. Because these FETs can be operated at less than 5 V, they may potentially be integrated with existing logic and display circuitry without significant signal amplification. This report demonstrates high‐mobility FETs using solution‐processed Ta2O5 dielectrics with drastically reduced power consumption; ≈95% reduction compared to that of the device with a conventional SiO2 gate dielectric. [ABSTRACT FROM AUTHOR]

[Display omitted] • To minimize surface defects and prevent ion migration, a passivation material with a greater binding energy is required. • Greater binding with the perovskite layer is achieved after post-passivation using octylammonium sulfonate salt, which lowers the hysteresis index to 0.01. • The passivation increases power conversion efficiency from 21.06% for the control to 24.37% for the devices treated with OAC. • The passivated perovskite films maintain more than 85% of their original PCE under 60% RH over 1600 h. Despite the recent exceptional rise in power conversion efficiency of perovskite solar cells (PSCs), surface defects and ion migration related instability are still present in PSCs. The chain length and binding energy of the passivation material play important roles in defect passivation, ion migration, moisture stability, and device-performance improvement. We synthesized three sulfonated ammonium compounds and investigated the effect of post-passivation with these compounds on ion-migration and stability. New materials with high binding energy include octylamine (OA) functionalized with sulfanilic acid (OAS), p-toluenesulfonic acid (OAT), and camphorsulfonic acid (OAC). The passivation improves power conversion efficiency (PCE) from 21.06% for the control to 24.37% for the devices treated with OAC. The champion device's hysteresis index decreased to 0.01 compared to 0.11 for the control device, which is the lowest reported so far. Furthermore, the passivated perovskite films retain over 85% of their initial PCE under 60% relative humidity for 1,600 h, and the device with OAC maintains over 90% of its initial operational long-term device stability without encapsulation for 600 h under 1 sun-illumination. [ABSTRACT FROM AUTHOR]

Fifty years after the Korean War (1950-1953), sometimes called the Forgotten War, the Koreas had receded into the back of the American mind. But the Axis of Evil address and the revelation of North Korea's nuclear weapons program have reeducated Americans to see the South as an ally and the North as a menacing regime. Despite an overwhelming antipathy to North Korea and a heightened sense of vulnerability, few Americans support a course of action more aggressive than diplomatic negotiations. [ABSTRACT FROM AUTHOR]

We report the preparation of Cu2S, In2S3, CuInS2 and Cu(In,Ga)S2 semiconducting films via the spin coating and annealing of soluble tertiary-alkyl thiolate complexes. The thiolate compounds are readily prepared via the reaction of metal bases and tertiary-alkyl thiols. The thiolate complexes are soluble in common organic solvents and can be solution processed by spin coating to yield thin films. Upon thermal annealing in the range of 200-400 °C, the tertiary-alkyl thiolates decompose cleanly to yield volatile dialkyl sulfides and metal sulfide films which are free of organic residue. Analysis of the reaction byproducts strongly suggests that the decomposition proceeds via an SN1 mechanism. The composition of the films can be controlled by adjusting the amount of each metal thiolate used in the precursor solution yielding bandgaps in the range of 1.2 to 3.3 eV. The films form functioning p-n junctions when deposited in contact with CdS films prepared by the same method. Functioning solar cells are observed when such p-n junctions are prepared on transparent conducting substrates and finished by depositing electrodes with appropriate work functions. This method enables the fabrication of metal chalcogenide films on a large scale via a simple and chemically clear process. [ABSTRACT FROM AUTHOR]

Since Michael Faraday and Joseph Henry 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. [ABSTRACT FROM AUTHOR]