ZnO nanorod arrays modified with Bi2S3 nanoparticles as cathode for efficient polymer solar cells

Abstract The surface modification of zinc oxide nanorod arrays (ZnO NRAs) is an effective way to improve electrical coupling between ZnO NRAs and organic active layer, and can decrease the surface defects of ZnO NRAs. In this work, ZnO NRAs grown on indium tin oxide (ITO) glass substrates are decorated with bismuth trisulphide (Bi 2 S 3 ) nanoparticles using successive ionic layer adsorption and reaction (SILAR) at room temperature. The resulted ZnO/Bi 2 S 3 core-shell NRAs are characterized by using different measurement techniques. SEM and TEM images confirm the homogeneous coverage of Bi 2 S 3 nanoparticles on the surface of ZnO NRAs. XPS and PL spectra demonstrate that surface defects of ZnO NRAs modified with 0.2 mM Bi 2 S 3 nanoparticles are effectively reduced. XRD spectra show the modification of the ZnO NRAs surface with Bi 2 S 3 can enhances the crystallinity of the active layer and ZnO NRAs, which will improve the absorption of sunlight, and help for the charge transfer in solar cells. Finally, hybrid solar cells with the structure of ITO/ZnO/Bi 2 S 3 /P3HT:PC 71 BM (or PTB7:PC 71 BM)/MoO 3 /Ag are for the first time fabricated. The solar cells based on the ZnO/0.2 mM Bi 2 S 3 core-shell NRAs with P3HT:PC 71 BM as active layer exhibit the nice performance with J sc , V oc , FF and η values equal to 9.51 ± 0.09 mA/cm 2 , 0.61 ± 0.01 V, 61.6 ± 0.6%, and 3.57 ± 0.05%, respectively. Besides, the PCE of the device based on the ZnO/0.2 mM Bi 2 S 3 core-shell NRAs with PTB7:PC 71 BM is improved to 6.35% from 4.88% of the reference device without Bi 2 S 3 coated. Increase of electrical coupling between ZnO NRAs and organic active layer and decline of the surface defects of ZnO NRAs lead to the performance improvement of devices with ZnO/Bi 2 S 3 core-shell NRAs, which implies that ZnO/Bi 2 S 3 core-shell NRAs made by SILAR method are promising electron transport materials in solar cells.