Light-induced pyroelectric effect as an effective approach for ultrafast ultraviolet nanosensing

Abstract

Zinc oxide is potentially a useful material for ultraviolet detectors; however, a relatively long response time hinders practical implementation. Here by designing and fabricating a self-powered ZnO/perovskite-heterostructured ultraviolet photodetector, the pyroelectric effect, induced in wurtzite ZnO nanowires on ultraviolet illumination, has been utilized as an effective approach for high-performance photon sensing. The response time is improved from 5.4 s to 53 μs at the rising edge, and 8.9 s to 63 μs at the falling edge, with an enhancement of five orders in magnitudes. The specific detectivity and the responsivity are both enhanced by 322%. This work provides a novel design to achieve ultrafast ultraviolet sensing at room temperature via light-self-induced pyroelectric effect. The newly designed ultrafast self-powered ultraviolet nanosensors may find promising applications in ultrafast optics, nonlinear optics, optothermal detections, computational memories and biocompatible optoelectronic probes.

Figure 1. Structure, characterization and design mechanism of self-powered ZPH PDs.

(a) Schematic demonstration of the structure of self-powered ZPH PDs. FTO acts as the transparent electrode. (b) Scanning electron microscopy images of self-powered ZPH PDs: (b1) side view of ZnO coated by perovskite, hole transport material (Spiro-OMeTAD) and Cu electrode in sequence (b2,b3) top view of ZnO NWs array (b2) before and (b3) after being spin-coated by perovskite. (c) XRD spectra of the perovskite (MAPbI₃) on the ZnO NWs layer. (d) Energy band diagram of a self-powered ZPH PD. Energies are expressed in electron volts, using the electron energy in vacuum as a reference. The energy levels of the conduction band edges of ZnO, MAPbI₃ and spiro-OMeTAD are at –4.35, –3.9 and –2.05 eV, respectively, and the valence band edge of the perovskite is at –5.4 eV. (e) Schematic illustration of the working mechanism of self-powered ZPH PDs. (f) I–V characteristics of the self-powered ZPH PDs under dark and 325-nm laser illumination with a power density of 3.7 mW cm⁻².

Figure 2. Pyroelectric effect enhanced performances of self-powered ZPH PDs.

(a) I–t characteristics of self-powered ZPH PDs under 325-nm illuminations with different power densities from 3.7 × 10⁻³ to 9.0 × 10⁻⁶W cm⁻², the inset is the enlarged I–t curves under the corresponding illumination conditions. (b) The short-circuit current response (c) and specific detectivity D* response of pyroelectric effect-combined photoexcitation process (black dots) and photoexcitation process (red dots), showing the enhancements by pyroelectric effect. Data reported in b,c were calculated from I–t curves acquired over 20 times within 30 days under different power densities.

Figure 3. Working mechanism of self-powered ZPH PDs.

(a) I–t characteristics of the self-powered ZPH PDs under 325 nm (top) and 442 nm (bottom) laser illuminations through an optical chopper with a time ratio of 1:1 at 100 Hz. (b) Enlarged plot of a single output period as shown in a for both 325- and 442-nm illuminations, divided into four stages, labelled as ‘I', ‘II', ‘III' and ‘IV'. (c) Schematic illustration of the working mechanism of pyroelectric effect-combined photoexcitation processes, corresponding to the four stages labelled in b.

Figure 4. Pyroelectric effect enhancements on response time of self-powered ZPH PDs.

(a) I–t response of the self-powered ZPH PDs to 325-nm illumination (power density of 1.8 mW cm⁻²) measured under different background environmental temperatures to confirm the pyroelectric effect. (b) I–t curves of the p-Si/ZnO PD biased at –2.0 V under 325-nm laser illumination with a power density of 2.6 × 10⁻⁴W cm⁻². (c–f) I–t curves of the ZPH PDs under different bias voltages of (c) 0.0 V, (d) 0.08 V, (e) 0.12 V and (f) 0.3 V to calculate the improved response time by pyroelectric effect. The inset indicates the corresponding circuit diagram with current heating effect (red glow around ZnO) and pyroelectric effect of ZnO (colour code of ZnO).