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

Abstract

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 (Bi2S3) nanoparticles using successive ionic layer adsorption and reaction (SILAR) at room temperature. The resulted ZnO/Bi2S3 core-shell NRAs are characterized by using different measurement techniques. SEM and TEM images confirm the homogeneous coverage of Bi2S3 nanoparticles on the surface of ZnO NRAs. XPS and PL spectra demonstrate that surface defects of ZnO NRAs modified with 0.2 mM Bi2S3 nanoparticles are effectively reduced. XRD spectra show the modification of the ZnO NRAs surface with Bi2S3 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/Bi2S3/P3HT:PC71BM (or PTB7:PC71BM)/MoO3/Ag are for the first time fabricated. The solar cells based on the ZnO/0.2 mM Bi2S3 core-shell NRAs with P3HT:PC71BM as active layer exhibit the nice performance with Jsc, Voc, FF and η values equal to 9.51 ± 0.09 mA/cm2, 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 Bi2S3 core-shell NRAs with PTB7:PC71BM is improved to 6.35% from 4.88% of the reference device without Bi2S3 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/Bi2S3 core-shell NRAs, which implies that ZnO/Bi2S3 core-shell NRAs made by SILAR method are promising electron transport materials in solar cells.