Hot-Air-Assisted Fully Air-Processed Barium Incorporated CsPbI2Br Perovskite Thin Films for Highly Efficient and Stable All-Inorganic Perovskite Solar Cells

Replacement of conventional organic cations by thermally stable inorganic cations in perovskite solar cells (PSCs) is one of the promising approaches to make thermally stable photovoltaics. However, conventional spin-coating and solvent-engineering processes in a controlled inert atmosphere hamper the upscaling. In this study, we demonstrated a dynamic hot-air (DHA) casting process to control the morphology and stability of all-inorganic PSCs which is processed under ambient conditions and free from conventional harmful antisolvents. Furthermore, CsPbI₂Br perovskite was doped with barium (Ba²⁺) alkaline earth metal cations (BaI₂:CsPbI₂Br). This DHA method facilitates the formation of uniform grain and controlled crystallization that makes stable all-inorganic PSCs which enables an intact black α-phase under ambient conditions. The DHA-processed BaI₂:CsPbI₂Br perovskite photovoltaics shows the champion power conversion efficiency (PCE) of 14.85% (reverse scan) for a small exposure area of 0.09 cm² and 13.78% for a large area of 1 × 1 cm² with excellent reproducibility. Interestingly, the hot-air-processed devices retain >92% of the initial efficiency after 300 h. This DHA method facilitates a wide processing window for upscaling the all-inorganic perovskite photovoltaics.

Stable, Ultralow Threshold Amplified Spontaneous Emission from CsPbBr3 Nanoparticles Exhibiting Trion Gain

Wet-chemically synthesized cesium lead halide nanoparticles have many attractive properties that make them promising as optical gain media, but generally suffer from poor stability under ambient conditions and an optical gain threshold that is widely believed to be dictated by the need for biexcitons. These conditions make it impractical for such particles to be utilized as gain media given the need to undergo repeated stimulated emission processes at above-threshold pump intensities over long periods of time. We demonstrate that the surface treatment of CsPbBr₃ nanoparticles with a mixture of PbBr₂, oleic acid, and oleylamine not only raises their fluorescence quantum yield to nearly unity and prolongs their stability in air from days to months, but it also dramatically increases their trion photoluminescence lifetime from ∼0.9 to ∼1.6 ns. Via a combination of time-resolved photoluminescence and transient absorption spectroscopy, we provide evidence for trion gain at sufficiently low pump intensities in which the likelihood of predominantly biexciton-based gain is small. We then show that, in line with theoretical prediction, the amplified spontaneous emission (ASE) threshold of a thin film of surface-treated CsPbBr₃ nanoparticles reduces to a record low of ∼1.2 μJ/cm² with a corresponding average exciton occupancy per nanoparticle of 0.62. The ultralow pump threshold and increased stability allow for stable ASE over millions of laser shots, paving the way for the deployment of these nanoparticles as viable solution-processed optical gain media.

Stable, Ultralow Threshold Amplified Spontaneous Emission from CsPbBr3 Nanoparticles Exhibiting Trion Gain

Wet-chemically synthesized cesium lead halide nanoparticles have many attractive properties that make them promising as optical gain media, but generally suffer from poor stability under ambient conditions and an optical gain threshold that is widely believed to be dictated by the need for biexcitons. These conditions make it impractical for such particles to be utilized as gain media given the need to undergo repeated stimulated emission processes at above-threshold pump intensities over long periods of time. We demonstrate that the surface treatment of CsPbBr₃ nanoparticles with a mixture of PbBr₂, oleic acid, and oleylamine not only raises their fluorescence quantum yield to nearly unity and prolongs their stability in air from days to months, but it also dramatically increases their trion photoluminescence lifetime from ∼0.9 to ∼1.6 ns. Via a combination of time-resolved photoluminescence and transient absorption spectroscopy, we provide evidence for trion gain at sufficiently low pump intensities in which the likelihood of predominantly biexciton-based gain is small. We then show that, in line with theoretical prediction, the amplified spontaneous emission (ASE) threshold of a thin film of surface-treated CsPbBr₃ nanoparticles reduces to a record low of ∼1.2 μJ/cm² with a corresponding average exciton occupancy per nanoparticle of 0.62. The ultralow pump threshold and increased stability allow for stable ASE over millions of laser shots, paving the way for the deployment of these nanoparticles as viable solution-processed optical gain media.