The nanowire length dependence of the photoresponse and Pyro-phototronic response in the ZnO-based heterojunctions

In this work, two series of ZnO/Si and ZnO/PEDOT:PSS heterojunctions are prepared with the ZnO nanowire length ranging from 200 to 1300 nm, and both the photoresponse and the Pyro-phototronic response to different nanowire lengths are well investigated under the illumination of different power density and laser wavelength. It is found that the photoresponses are strongly dependent on the nanowire length. However, the optimal length, as well as the performances, is quite different for the two heterostructures as it is 400 nm in the ZnO/Si heterojunction with the responsivity of 67.6 mA/W and 0.565 mA/W under + 1 V and zero bias voltage, respectively, and turns to 200 nm in the ZnO/PEDOT:PSS heterojunction with the responsivity reaching 107.9 A/W and 0.199 mA/W under + 0.4 V and zero bias voltage, respectively. Moreover, when the Pyro-phototronic effect is introduced, the photoresponses are all greatly improved with an increment as large as 1589%. Meanwhile, an ultra-broadband response range of 360–1550 nm, which is far beyond the bandgap of both the ZnO and the heterojunctions, is also achieved in the two heterostructures. However, the optimal response wavelength, which is observed at the 450 nm and 360 nm for the ZnO/Si and ZnO/PEDOT:PSS heterostructures, respectively, varies considerably. These tremendous differences in the two heterostructures can be ascribed to their different light absorption, carriers’ transport and separation, pyroelectric potential, and band alignment properties. Two series of ZnO/Si and ZnO/PEDOT:PSS heterojunctions are prepared, and both the photoresponse and the Pyro-phototronic response to different nanowire lengths are well investigated. The photoresponses are all strongly dependent on the nanowire length. However, the optimal length, as well as the performances, is quite different for the two heterostructures. Moreover, by introducing the Pyro-phototronic effect, the photoresponses are all greatly improved with an increment as large as 1589%, and meanwhile, an ultra-broadband response range of 360–1550 nm is also achieved. • Photoresponse and Pyro-phototronic response to different ZnO nanowire lengths are investigated. • Photoresponses are strongly dependent on the nanowire length but with quite different optimal lengths and performances. • Photoresponses are greatly improved by introducing Pyro-phototronic effect with an increment reaching up to 1589%. • An ultra-broadband response range of 360 to 1550 nm, far beyond the bandgap of the heterojunctions, is obtained.