Organic-inorganic halide perovskites are making breakthroughs in a range of optoelectronic devices. Reports of >23% certified power conversion efficiency in photovoltaic devices, external quantum efficiency >21% in light-emitting diodes (LEDs), continuous-wave lasing and ultralow lasing thresholds in optically pumped lasers, and detectivity in photodetectors on a par with commercial GaAs rivals are being witnessed, making them the fastest ever emerging material technology. Still, questions on their toxicity and long-term stability raise concerns toward their market entry. The intrinsic instability in these materials arises due to the organic cation, typically the volatile methylamine (MA), which contributes to hysteresis in the current-voltage characteristics and ion migration. Alternative inorganic substitutes to MA, such as cesium, and large organic cations that lead to a layered structure, enhance structural as well as device operational stability. These perovskites also provide a high exciton binding energy that is a prerequisite to enhance radiative emission yield in LEDs. The incorporation of inorganic and layered perovskites, in the form of polycrystalline films or as single-crystalline nanostructure morphologies, is now leading to the demonstration of stable devices with excellent performance parameters. Herein, key developments made in various optoelectronic devices using these perovskites are summarized and an outlook toward stable yet efficient devices is presented.

Solar cells based on organic-inorganic halide perovskite are now leading the photovoltaic technologies due to their high power conversion efficiency. Recently, there have been debates on the microstructure related defects in metal halide perovskites (grain size, grain boundaries, etc.) and a widespread view is that large grains are a prerequisite to suppress non-radiative recombination, and improve photovoltaic performance although opinions against it also exist. Herein, we employ blends of methylammonium lead iodide perovskite with an insulating polymer (polyvinylpyrrolidone, PVP) that offer the possibility to tune the grain size in order to obtain a fundamental understanding of the photoresponse at the microscopic level. We provide, for the first time, spatially-resolved details of the microstructure in such blend systems via Raman mapping, light beam induced current (LBIC) imaging and conductive atomic force microscopy. Although the polymer blend systems systematically alter the morphology by creating small grains (more grain boundaries), they reduce non-radiative recombination 2 within the film and enhance its spatial homogeneity of radiative recombination. We attribute this to a reduction in the density of bulk trap states, as evidenced by an order of magnitude higher photoluminescence intensity and a significantly higher open-circuit voltage when the polymer is incorporated into the perovskite films. The solar cells employing blend systems also show nearly hysteresis-free power conversion efficiency ~17.8%, as well as a remarkable shelflife stability over 100 days.

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