Device Performance Improvement of WSe2 Phototransistors Incorporated with CsPbI3 Perovskite Quantum Dots

Phototransistors that integrate WSe2 with CsPbI3 quantum dots are fabricated to combine the merits of both materials in photo detecting performances. The hybrid devices demonstrate a substantially enhanced photoresponsivity, reaching up to 10.38 A/W, an appreciable specific detectivity of 7.78 × 1011 Jones, and an external quantum efficiency of 2.43 × 103%. Moreover, the hybridization of the quantum dots does not show any lagging in the photoresponse of the WSe2 devices. To explore the carrier migration in the hybrid structure, we investigated two mechanisms, namely, the direct charge transfer in the photogating effect and the exciton transfer mediated by the Förster resonance energy transfer (FRET) process. The time-resolved photoluminescence (TRPL) spectroscopy is used to analyze the proportion of these mechanisms. The results reveal that the FRET mechanism, which leads to a short fluorescence lifetime in TRPL, dominates the photoresponse in the device. As more layers of quantum dots are spin-coated on WSe2, the photogating effect, which corresponds to a longer fluorescence lifetime, becomes more manifested and consequently delays the photoresponse of the device. This study demonstrates a promising design of a photodetector that combines high responsivity with rapid response speed, through the introduction of quantum dots with high photo absorption, and the FRET mechanism in the heterostructure.