Critical Role of Carrier Cooling Mechanism in WS2/CsPbBr3 Hybrid Nanocomposites for Enhanced Photodetector Performances

Heterostructures and nanocomposites comprising transition metal dichalcogenides (TMDCs) and halide perovskite nanocrystals (NCs) are prominently used in several optoelectronic devices. Hot carriers (HCs) are the charge carriers possessing higher kinetic energy than surrounded thermal distributions. Properly utilizing these HCs by slowing down their cooling mechanism reduces the energy losses in optoelectronic devices. Herein, employing the femtosecond transient absorption spectroscopy (fs-TAS) technique, the slowdown processes of HC relaxations are reported in WS2/CsPbBr3 hybrid-nanocomposites due to the hot-phonon bottleneck. HCs relaxation time increases from ≈6 ps in CsPbBr3 NCs to ≈10 ps in WS2/CsPbBr3 nanocomposites at an excitation fluence of 17.7 µJ cm-2. The maximum HCs temperature TC increased to 1181 K in WS2/CsPbBr3 nanocomposites with an observed TC of 856 K in pristine NCs. The electron transfer process from NCs to WS2 nanosheets has been observed in these nanocomposites with time component t2 ≈38.0-102.4 ps in pristine NCs and 20.9-66.9 ps in nanocomposites, became faster at excitation-fluence of 17.7-99.8 µJ cm-2. Furthermore, a significant enhancement in nanocomposite-based photodetector confirmed the efficient charge transfer at the heterojunction, resulting ≈400%, ≈420%, and ≈200% increase in the photocurrent, responsivity, and detectivity, respectively, compared to the pristine devices.