Photosensitive Field-Effect Transistor with Enhanced Photoamplification Mediated by Charge Transfer in a Heterostructure of α-CsPbI3 Nanocrystals and Two-Dimensional WS2

Hybrid heterostructure-based phototransistors are attractive owing to their high gain induced by the photogating effect. However, the absence of an in-plane built-in electric field in the single-channel-layer transistor results in a relatively higher dark current and requires a large operating gate voltage of the device. Here, we report air-stable cesium lead iodide/tungsten di-sulfide (${\mathrm{Cs}\mathrm{Pb}\mathrm{I}}_{3}/{\mathrm{WS}}_{2}$) mixed-dimensional heterostructure-based photo-field-effect-transistors (photo-FETs) with asymmetric metal electrodes ($\mathrm{Cr}/{\mathrm{WS}}_{2}/\mathrm{Au}$), exhibiting extremely low dark current (approximately ${10}^{\ensuremath{-}12}$ A) with a responsivity of approximately ${10}^{2}$ A/W at zero gate bias. The Schottky-barrier- (${\mathrm{WS}}_{2}/\mathrm{Au}$ interface) induced rectification characteristics in the channel accompanied by the excellent photogating effect from solution-processed \ensuremath{\alpha}-phase ${\mathrm{Cs}\mathrm{Pb}\mathrm{I}}_{3}$ nanocrystal sensitizers, resulting in gate-tunable broadband photodetection with a very high responsivity (approximately ${10}^{4}$ A/W) and excellent sensitivity (approximately ${10}^{6}$). Most interestingly, the device shows superior performance even under high-humidity (50--65%) conditions owing to the formation of cubic \ensuremath{\alpha}-phase ${\mathrm{Cs}\mathrm{Pb}\mathrm{I}}_{3}$ nanocrystals with a relatively smaller lattice constant (a = 6.2315 \AA{}) and filling of surface vacancies (${\mathrm{Pb}}^{2+}$ centers) with the sulphur atoms from the ${\mathrm{WS}}_{2}$ layer, thus protecting it from environmental degradation. These results emphasize an exciting strategy for developing mixed-dimensional hybrid heterostructure-based phototransistors for futuristic integrated nano-optoelectronic systems.