Performance of ZnO nanorod-based perovskite solar cells

Abstract

In recent years, perovskite solar cells have obtained a rapid development due to their large light absorption coefficient, low-cost and high power conversion efficiency (PCE). In this study, the one-dimensional ordered ZnO nanorod arrays were prepared on FTO glasses by chemical bath deposition at low temperature. TiO2 nanoparticles from different kinds of solution were further spin-coated onto the ZnO nano arrays to form ZnO/TiO2 composite nano arrays, as the electron transfer layer in perovskite solar cells. The microstructure of different ZnO/TiO2 composite nano arrays and their corresponding photovoltaic performance of the solar cells were investigated. It was found that the cells based on ZnO nano arrays treated by TiO2 nanoparticle paste exhibit the highest PCE. The influence of TiO2 paste concentration on the photovoltaic performance of cells was further investigated. It indicated that the cell achieves best photovoltaic performance at TiO2 paste concentration of 0.1 mol/L: open circuit voltage ( V oc) of 0.93 V, short circuit current ( J sc) of 15.30 mA cm−2, filling factor ( FF ) of 43% and PCE of 6.07%. The treatment of TiO2 paste on ZnO nano arrays results in perovskite nanoparticles can effectively fill into the cracks between ZnO nanorods and a flat and compact perovskite layer can also form on the top of ZnO nano arrays. These effectively enhance the loading of perovskite and suppress the recombination between carriers in cells, resulting in an improved photovoltaic performance. A further treatment of ZnO/TiO2 paste arrays with TiCl4 aqueous solution can significantly improve the photovoltaic performance of the perovskite solar cells: V oc=0.99 V, J sc=19.09 mA cm−2, FF =58%, and PCE of 11%. The TiCl4 treatment of ZnO/TiO2 composite arrays introduces small TiO2 nanoparticles (~3 nm) into nano arrays. The small nanoparticles can fully fill the cracks between the nanorods and create better contact between perovskite (both in top layer and the arrays) and nano arrays. The photo induced carrers can rapidly transfer via ZnO nanorods to the conductive substrates. Furthermore, the introduce of small TiO2 nanoparticles also increases the surface area of electrode to absorb more perovskite, and hence improve the adsorption of light and result in an improved photovoltaic performance of the cells.