Ambipolar Photoresponse of CsPbX₃-ZnO (X = Cl, Br, and I) Heterojunctions

Abstract

All-inorganic perovskite CsPbX3 (X = Cl, Br, and I) quantum dots (QDs) are emerging as attractive materials for photodetectors due to their prominent positive photoresponse. In this work, ambipolar photodetectors were constructed based on heterojunctions of CsPbX3 QDs and ZnO nanocrystals (NCs). The transition between the positive photoconductivity (PPC) and negative photoconductivity (NPC) was successfully controlled not only by the drain-source voltage (V DS) but also by the excitation wavelength and CsPbX3 crystal size. A high responsivity (R), on–off ratio (η), and detectivity (D*) were achieved for NPC (R = 1046 mA/W, η = 281, and D* = 1.65 × 1011 Jones), with PPC (R = 146 mA/W, η = 64, and D* = 1.54 × 1011 Jones) simultaneously revealed in the same device. A general mechanism combining the type-II heterojunction, the component and size-related band structure, and most critically the in-band trap states of the perovskites was established for understanding the unique ambipolar property. It exhibits application potential in developing functional photodetectors, memristors, and optical logic devices.

Negative Photoconductivity: Bizarre Physics in Semiconductors

“…Metal halide perovskites are widely explored in photodetection applications. ,− The charge carrier generation under illumination leads to positive photoconductivity in these materials. A lot of reports demonstrate the PPC in perovskite materials. − Recently, the NPC was reported in halide perovskites under certain conditions. − In this line, Yuan et al presented the NPC under illumination in Cs 4 PbBr 6 perovskite single crystals . A significant amount of reduction was observed in the current under illumination than in the dark current.…”

UV–vis–IR Broad Spectral Photodetectors Based on VO2–ZnO Nanocrystal Films

“…The indium tin oxide (ITO) glass (15 Ω/□) was cleaned with acetone, ethanol, and deionized water. The interdigital electrodes were patterned by laser etching and acid washing of the ITO glass with a gap width of 200 μm. , On a heating stage of 150 °C, the VO 2 –ZnO NCs were deposited onto the ITO interdigital electrodes by the NC-mist deposition of the VO 2 –ZnO NC solution, forming a lateral structured ITO/VO 2 –ZnO NCs/ITO device. The photodetection properties were measured by a Keithley 2636B source meter.…”

“…As a wide band gap semiconductor, ZnO is stable and has high carrier mobility, which can potentially improve the charge transport and enhance the device performance. In photovoltaic devices, ZnO films composed of ZnO nanocrystals (NCs) can serve as the electron transport layer. − In photodetectors, hybridization of ZnO with a second semiconductor, e.g., perovskite, could achieve an ambipolar photoresponse, higher switching ratio, faster response speed, and higher response and detection rate than compared to corresponding monophase devices. − …”

“… 9 − 12 In photodetectors, hybridization of ZnO with a second semiconductor, e.g., perovskite, could achieve an ambipolar photoresponse, higher switching ratio, faster response speed, and higher response and detection rate than compared to corresponding monophase devices. 13 − 16 …”

Sensitization of ZnO Photoconductivity in the Visible Range by Colloidal Cesium Lead Halide Nanocrystals

“…There is also an increasing number of studies considering photoconductive perovskite-containing materials as elements of artificial synapses [ 40 , 41 , 42 , 43 , 44 ]. The published results on the effect of perovskite nanocrystals on the photoconductivity of ZnO mainly concern monohalide perovskites with an organic [ 45 , 46 , 47 , 48 , 49 ] or inorganic cation [ 4 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 ], while the use of mixed halide perovskites as sensitizers use is also discussed in the literature [ 44 , 58 , 59 , 60 ], however has not been systematically studied so far.…”