Giant photo-amplification in air-stable α-CsPbI₃ nanocrystals / WS₂ 0D / 2D mixed-dimensional phototransistor with asymmetric contacts

Hybrid heterostructures comprising of 2D transition metal dichalcogenides (TMDs) and 0D perovskite nanocrystals having excellent photosensitive characteristics offer the possibility to achieve next generation optoelectronic devices with superior functionalities. However, the absence of any in-plane built-in electric field in these single channel layer transistors results in relatively higher dark current and a larger gate voltage is necessary to deplete the channel. To overcome these limitations, air stable Cesium lead iodide/Tungsten di-sulfied (CsPbI₃/WS₂) mixed dimensional heterostructure based phototransistors are reported with asymmetric metal electrodes (Cr/WS₂/Au), exhibiting extremely low dark current (~10^-12 A) with a high responsivity (~ 10² A/W) at zero gate bias. In these devices, the Schottky barrier at WS₂/Au interface accompanied with excellent photoabsorbing attributes of solution-processed α-phase CsPbI₃ sensitizers, result in gate-tunable broadband phototransistor with high responsivity (~10⁴ A/W). Most interestingly, the device shows superior performance even under high humidity (50-65%) conditions owing to the formation of cubic α-phase CsPbI₃ with a relatively smaller lattice constant (a = 6.2315 Å). These outcomes highlight a novel strategy to utilize the metal semiconductor Schottky junction in combination with photosensitive perovskite NCs decorated TMD based hybrid heterostructures for developing large-scale optoelectronic devices.