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  • Title: Acoustic-optical phonon up-conversion and hot-phonon bottleneck in lead-halide perovskites.
    Author: Yang J, Wen X, Xia H, Sheng R, Ma Q, Kim J, Tapping P, Harada T, Kee TW, Huang F, Cheng YB, Green M, Ho-Baillie A, Huang S, Shrestha S, Patterson R, Conibeer G.
    Journal: Nat Commun; 2017 Jan 20; 8():14120. PubMed ID: 28106061.
    Abstract:
    The hot-phonon bottleneck effect in lead-halide perovskites (APbX3) prolongs the cooling period of hot charge carriers, an effect that could be used in the next-generation photovoltaics devices. Using ultrafast optical characterization and first-principle calculations, four kinds of lead-halide perovskites (A=FA+/MA+/Cs+, X=I-/Br-) are compared in this study to reveal the carrier-phonon dynamics within. Here we show a stronger phonon bottleneck effect in hybrid perovskites than in their inorganic counterparts. Compared with the caesium-based system, a 10 times slower carrier-phonon relaxation rate is observed in FAPbI3. The up-conversion of low-energy phonons is proposed to be responsible for the bottleneck effect. The presence of organic cations introduces overlapping phonon branches and facilitates the up-transition of low-energy modes. The blocking of phonon propagation associated with an ultralow thermal conductivity of the material also increases the overall up-conversion efficiency. This result also suggests a new and general method for achieving long-lived hot carriers in materials.
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