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.
Highlights
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
Several mechanisms have been suggested for the hot carrier dynamics on sub-picosecond timescales in lead-halide perovskites[27,28,29], a comprehensive understanding of the phonon bottleneck effect occurring on longer timescales is still lacking
On the basis of the fabrication methods, all samples are optimized in conventional photovoltaic applications, which are sufficiently stable during the measurements to ensure that accurate and reproducible experimental data are obtained
Summary
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. The blocking of phonon propagation associated with an ultralow thermal conductivity of the material increases the overall up-conversion efficiency This result suggests a new and general method for achieving long-lived hot carriers in materials. A significant hot-phonon bottleneck effect in carrier thermalization was observed in lead-halide perovskites[8,9], which indicates potential applications of these kinds of materials in the advanced concept of hot carrier optoelectronics. Cooling of photo-generated hot carriers in a material dissipates the absorbed optical energy as lattice heat via longitudinal optical (LO) phonon emission and decay. Thermalization by this mechanism leads to about 50% of the energy losses in a traditional single junction solar cell[15]. We compare the hot carrier and phononic properties among four typical kinds of lead-halide perovskites used in photovoltaics, including CH3NH3PbI3 (MAPbI3), HC(NH2)2PbI3 (FAPbI3), CcaHtio3NnsH(3MPbABþr[3],
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