Lawrence Berkeley National Laboratory

Controllable synthesis of tin-doped all-inorganic perovskite (e.g. CsPb1-XSnXBr3) 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 CsPb1-XSnXBr3 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 CsPb1-XSnXBr3 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 CsPb0.966Sn0.034Br3 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 CsPb0.966Sn0.034Br3 nanocrystals that can make the electron injection barrier thin enough to allow electron tunneling in the photodetectors for photomultiplication.