Research On Preparation, Process And Performance Of Organic-Inorganic Hybrid Solar Cells Based On Perovskite

In recent years, organic-inorganic hybrid perovskites, as the most potential optoelectronic materials, have attracted much attention. Solar cells based on halide perovskite have made rapid progress in just a few years. In particular, perovskite solar cells (PSCs) with the mesoporous structure based on inorganic metal oxide semiconductors as electron transport materials present high photoelectric conversion efficiency. With the advantages of high transmittance, long carriers lifetime, and controllable morphology, ZnO nanorods (NRs) materials have obtained good applications in organic-inorganic hybrid solar cells and photocatalysis. However, such research on the application of ZnO NRs-based PSCs have received less attention. Herein, the research focusing on the preparation process and the optimization of photovoltaic performance for PSCs based on ZnO NRs are carried out. The results obtained are as follows.(1) The ZnO NRs were prepared by a typical two-step method. Firstly, the ZnO seed layer was prepared by sol-gel method, and then ZnO NRs were grown on the ZnO seed layer through hydrothermal process. When the solution concentrations of ZnO NRs were 20mM,25 mM,30 mM and 35 mM, the diameter of ZnO NRs was ranged from 60 nm to 72nm and the length was ranged from 300 nm to 460 nm. Based on the ZnO NRs, which acted as an electron transport layer, the perovskite absorption layer was deposited by the two-step solution method. Then Spiro-OMeTAD was spin-coated as a hole transport layer. As a result, PSCs based on ZnO NRs with the solution concentration of 25 mM gained the highest PCE of 7.65%, and the corresponding perovskite film was uniform, smooth, and with good crystallinity. The diameter and the length of ZnO nanorods was meaured as about 72 nm and 320 nm, respectively.(2) The PCE of PSCs was optimized by controlling the immersing time of CH3NH3I of 20 s,30 s,40 s,50 s, and 60 s. With the increase of immersing time, the UV-vis light absorption of perovskite films increased first and then decreased. This is because that the insufficient immersing could lead to the incomplete reaction of PbI2 and CH3NH3I, and the excessive immersing could lead to the redissolution of generated perovskite. As a result, we attained a dense, uniform, and less porous perovskite film, and the highest PCE of PSCs was 8.62% with the immersing time of 40 s.(3) Upon the above work, the solution concentration of ZnO NRs and the immersing time of CH3NH3I were optimized as 25 mM and 40 s, respectively, and then the ZnO NRs layer was modified by coating a thin layer of PCBM. Compared with the sample without modification of PCBM and samples with modification of PCBM using different spin-coating speed of 4000 r/m,5000 r/m, and 6000 r/m, the sample using 5000 r/m presented the highest PCE of 11.05%. As shown in the 2D and 3D AFM images, modification with PCBM can contribute to attain a highly flat, uniform, and pinhole-free perovskite film. The RMS roughness decreases from 19.8nm to 15.6 nm, due to the modification of PCBM. In addition, the light absorption of perovskite layer based on PCBM-modified ZnO nanorods was enhanced, as seen in the UV-vis absorption spectra.