Low-temperature synthesis of all-inorganic perovskite nanocrystals for UV-photodetectors

Abstract

Controllable synthesis of tin-doped all-inorganic perovskite (e.g. CsPb_1−XSn_XBr₃) nanocrystals while maintaining tin at the divalent state is of great importance for tuning their optoelectronic properties by changing the chemical composition and geometrical size; however, this remains a non-negligible challenge. In contrast to the conventional high-temperature (>150 °C) synthesis reaction that would more likely facilitate oxidation of divalent Sn²⁺ to quadrivalent Sn⁴⁺, this work demonstrates a facile low-temperature (105–150 °C) hot-injection method to synthesize quantum-confined Sn²⁺-doped CsPb_1−XSn_XBr₃ nanocrystals with sizes ranging from ∼6.2 nm to ∼8.3 nm depending on the reaction temperature. The optimized reaction temperature of 135 °C led to a Sn²⁺-doping ratio of 3.4% in CsPb_1−XSn_XBr₃ nanocrystals which exhibited uniform nanoplatelets with an average lateral size of ∼7.4 nm. Furthermore, for the first time, we show that the perovskite nanocrystals are promising for the development of low-cost and trap-assisted photomultiplication UV-photodetectors, and the photodetectors based on CsPb_0.966Sn_0.034Br₃ nanocrystals exhibited wavelength-dependent detectivities in the magnitude of 10¹¹ Jones for UV light extending from 310 nm to 400 nm at a reverse bias of −7 V. The high EQE of ∼1940% at around 340 nm indicates that the devices had a gain at the large reverse bias condition, which is attributed to the formation of interfacial traps by CsPb_0.966Sn_0.034Br₃ nanocrystals that can make the electron injection barrier thin enough to allow electron tunneling in the photodetectors for photomultiplication.