High-performance flexible ultraviolet photoconductors based on solution-processed ultrathin ZnO/Au nanoparticle composite films

Abstract

Transparent ultraviolet (UV) ZnO thin film photoconductors are expected to have great applications in environmental monitoring, large-area displays, and optical communications, and they have drawn enormous interests in recent years. However, at present their performances are not satisfactory: the responsivity R (a parameter characterizing the sensitivity of the device to light) is not high (<1.0 × 10(3) AW(-1)), and the transparency T is not high either (<80%). Realizing high R and high T remains a big challenge today. In this paper, by employing solution-processed ultrathin ZnO/Au nanoparticle composite films, R as high as 1.51 × 10(5) AW(-1) and T of over 90% are achieved. High values for detectivity D* and linear dynamic range LDR are also obtained, which are 2.05 × 10(15) Jones and 60 dB, respectively. Moreover, such high-performance devices can be fabricated on flexible PET (polyethylene terephthalate) substrates.

Figure 1

(a) Schematic illustration, (b) cross-sectional SEM image, (c) device flexibility, (d) device transparency and (e) patterned ITO electrodes on the substrate of the fabricated UV photoconductor (L = 50, 100, 150, and 200 μm, W = 5000 μm).

Figure 2

(a), (b), (c) and (d) are the AFM images of the ZnO films formed with different deposition cycles. (e)SEM image, (f)EDS measurement and (g)XPS analysis of the ZnO film.

Figure 3

(a) TEM image, (b) absorption spectrum and (c) XRD pattern of the Au NPs. (d) AFM image of the as-cast Au NPs on ZnO film. (e) Photograph of four highly transparent ZnO/Au NPs films on quartz substrate, (f) UV-Vis transmission spectra. The inset in (a) is the Au NPs size histograms and that in (b) is the Au NPs solution.

Figure 4

(a) Transfer and (b) output characteristics of the 3T ZnO/Au NPs FET (L = 50 μm, W = 2000 μm). (c) Transfer characteristics of the device in dark and under white light illumination with various intensities. (d) P and R versus V_GS under white light illumination with a power of 242.3 μWcm⁻².

Figure 5

(a) Optical transmittances of the photoconductors. (b) Spectral R of the photoconductor based on the 3T ZnO/Au NPs film (L = 50 μm, V = 50 V), the inset shows the response of I-V curve to illumination light wavelength (10.6 μWcm⁻²). (c) I-V curves of the photoconductors (with and without Au NPs) in dark and under 350 nm UV light illumination with an intensity of 10.6 μWcm⁻² (L = 50 μm); (d) I-V curves of the photoconductors (with Au NPs) with different channel lengths under 350 nm UV light illumination (10.6 μWcm⁻²).

Figure 6

The 3T ZnO/Au NPs photoconductor (L = 50 μm): (a) Calculated photogain and R and (b) calculated D* under 350 nm UV light illumination (10.6 μW/cm²). (c) LDR measured under white light. (d) Current versus time under various white light illumination intensities under a bias of 50 V. (e) On-off switching properties measured under 350 nm UV light illumination (10.6 μWcm⁻²) under a bias of 50 V. (f) Time resolved photocurrent: rise and decay (inset) curves.