The Preparation And Photodetection Property Of PbS/ZnO Nanocomposites

Photoelecttic detectror based on nanomaterials has a broad application. Nano ZnO is a good kind of UV detector material, its good performance and low cost makes it be one of the most potential UV photodector material; Nano PbS is widely used as a infrared detecter, it is reliable, superior performance and low cost. But how to impove the photodetection performance of nano ZnO, PbS and develop a photodetector of UV-VIS-IR has important scientific and practical significance. In this paper, I prepare nano PbS and PbS/ZnO nanocomposites, using XRD, Raman, TEM, XPS, UV-VIS-IR spectrum, PL to study its photodetection and the effect of PbS/ZnO interface. The main contents and conclusions are as follows:1. Nano PbS is prepared by Pb(NO3)2 and Na2 S. XRD showed that nano PbS is galena structure, and PbO?PbSO4 phase is observed. The average crystal size of nano PbS is about 18.2 nm. The nano PbS has a strong absorption at UV-VIS-IR. A photodetector with the structure of FTO/nano PbS/FTO is prepared by coating. The photdetection performance is tested under the irradiation of UV-VIS-IR lighting. The results show that the photodetection under the irradiation of UV(365 nm) and VIS(470 nm, 530 nm, 630 nm) is good, but its photoresponse time is long; the photoresponse current under the irradiation of near-infrared(750 nm, 850 nm, 940nm) light is small.2. Two PbS/ZnO nanocomposites with the same Pb/Zn molar ratio of 1:12 and different PbS/ZnO interface were prepared by depositing PbS nanocrystals on nano ZnO with the reaction between Pb(NO3)2 and through changing the sequence of adding Pb(NO3)2 and Na2 S to the nano ZnO suspension: A) first adding Pb(NO3)2 followed by adding Na2S(denoted PbS/ZnO-A); B) first adding Na2 S followed by adding Pb(NO3)2(denoted PbS/ZnO-B). The characterizations indicate that PbS/ZnO-B has an interface of PbS nanocrystal closely contacted to ZnO nanocrystal while PbS/ZnO-B has an interface of a disordered layer between PbS nanocrystal and ZnO nanocrystal. It is found for the first time that the PbS/ZnO interface plays an important role in their photodetection performance. PbS/ZnO-A exhibits much higher photoresponse current and lower rise and recovery time than both PbS/ZnO-B and a mixture of nano PbS and ZnO with the same Pb/Zn molar ratio as PbS/ZnO-A for visible and near-infrared photodetection. PL and the impedance measurement in dark and irradiation reveal that the superior photodetection performance of PbS/ZnO-A over PbS/ZnO-B is attributed to its lower e-h recombination and migration resistance under the irradiation of visible and infrared light due to its very good PbS/ZnO interface of PbS nanocrystals closely attached ZnO nanocrystals, through which photogenerated electrons inject efficiently from the conduction band of PbS to that of ZnO. In contrast, the defect sites in the disordered layer between PbS nanocrystal and ZnO nanocrystal for PbS/ZnO-B act as e-h recombination centers, significantly decreasing the e-h separation efficiency.