Search

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 [...]

UnlabelledOrganic-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 acidicPedotPSS) exhibit a device efficiency of over 12% and improved device stability in air. As an alternative toPedotPSS, 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.

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]

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]

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]

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]