Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 138, Issue 27, Pages 8603-8611Publisher
AMER CHEMICAL SOC
DOI: 10.1021/jacs.6b04661
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- Center for Sustainable Energy at Notre Dame (cSEND) through the Patrick and Jana Eilers Graduate Student Fellowship
- Division of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences of the U.S. Department of Energy [DE-FC02-04ER15533]
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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 CsPbBrxI3-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.
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