Transformation of Sintered CsPbBr3 Nanocrystals to Cubic CsPbI3 and Gradient CsPbBrxI3–x through Halide Exchange

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• 作者：Jacob B. Hoffman ; A. Lennart Schleper ; Prashant V. Kamat
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：July 13, 2016
• 年：2016
• 卷：138
• 期：27
• 页码：8603-8611
• 全文大小：618K
• 年卷期：0
• ISSN：1520-5126

文摘

All-inorganic cesium lead halide (CsPbX₃, X = Br^–, I^–) perovskites could potentially provide comparable photovoltaic performance with enhanced stability compared to organic–inorganic lead halide species. However, small-bandgap cubic CsPbI₃ has been difficult to study due to challenges forming CsPbI₃ in the cubic phase. Here, a low-temperature procedure to form cubic CsPbI₃ has been developed through a halide exchange reaction using films of sintered CsPbBr₃ nanocrystals. The reaction was found to be strongly dependent upon temperature, featuring an Arrhenius relationship. Additionally, film thickness played a significant role in determining internal film structure at intermediate reaction times. Thin films (50 nm) showed only a small distribution of CsPbBr_xI_3–x species, while thicker films (350 nm) exhibited much broader distributions. Furthermore, internal film structure was ordered, featuring a compositional gradient within film. Transient absorption spectroscopy showed the influence of halide exchange on the excited state of the material. In thicker films, charge carriers were rapidly transferred to iodide-rich regions near the film surface within the first several picoseconds after excitation. This ultrafast vectorial charge-transfer process illustrates the potential of utilizing compositional gradients to direct charge flow in perovskite-based photovoltaics.