CsPbX3 -ITO (X = Cl, Br, I) Nano-Heterojunctions: Voltage Tuned Positive to Negative Photoresponse.

All-Inorganic perovskite CsPbX3 (X = Cl, Br, I) quantum dots (QDs) have attracted tremendous attention in the past few years for their appealing performance in optoelectronic applications. Major properties of CsPbX3 QDs include the positive photoconductivity (PPC) and the defect tolerance of the in-band trap states. Here it is reported that when hybridizing CsPbX3 QDs with indium tin oxide (ITO) nanocrystals to form CsPbX3 -ITO nano-heterojunctions (NHJs), a voltage tuned photoresponse-from PPC to negative photoconductivity (NPC) transform-is achieved in lateral drain-source structured ITO/CsPbX3 -ITO-NHJs/ITO devices. A model combining exciton, charge separation, transport, and most critical the voltage driven electron filling of the in-band trap states with drain-source voltage (VDS ) above a threshold, is proposed to understand this unusual PPC-NPC transform mechanism, which is different from that of any known nanomaterial system. This finding exhibits potentials for developing devices such as photodetectors, optoelectronic switches, and memories.