Study On Preparation And Photoelectric Chemical Properties Of Perovskite Solar Cells

The perovskite solar cells (PSCs) have been attracting broad attention due to the rapid increase of power conversion efficiency (PCE) in recent years. They have developed into a kind of solar cells with high efficiency, low cost, simple procedure and diverse structure because of the low recombination rate, high carrier mobility and considerably long diffusion length in the perovskite materials. However, the intrinsic mechanism for such perovskite devices is still obscure and the devices are extremely sensitive to external environment. In this study, based on the thin-film planar PSC with TiO2 as the blocking layer, we explore the effect of humidity on the micro morphology and efficiency of PSCs under fully open-air conditions and subsequently the probable mechanism. Moreover, we prepared the devices based on ZnO nanowires as the scaffold via two steps solution-processed method.1. we investigated the effect of humidity on the micro morphology and efficiency of PSCs under fully open-air conditions and subsequently the probable mechanism.The perovskite absorber layer in organic-inorganic hybrid perovskites (e.g.,CH3NH3PbI3) solar cells (PSCs) is so sensitive to environmental humidity during the preparation, that most of the fabrication of the devices is accomplished in the glove box. Here, the procedure fully under open-air conditions we employed is the simplification of the PSCs on account of its advantage for large-scale manufacturing. The micro morphology and structure were characterized by a field emission scanning electron microscope (FE-SEM, SU8020), X-ray diffraction (D/MAX2500V) and ultraviolet-visible absorbance spectra. The growing mechanism of perovskite crystal was explored. Additionally, the probable mechanism of degradation was discussed based on the probable reaction with water. We found that the conversion efficiency of PSCs increased from 0.95% to 5.81% as humidity decreased from 70% to 20% in the air, which could be ascribed to the increase coverage of perovskite absorber and decrease of the defect states, subsequently resulting in improving photovoltaic performance (Voc, Jsc, FF and etc.) of the cells remarkably.2. we prepared the devices based on ZnO nanowires as the scaffold via two steps solution-processed method.1-D highly ordered array and flowerlike ZnO nanowires was prepared via hydrothermal process, which based on the perovskite solar cells were fabricated. The micro morphology, structure and compositon were characterized by SEM, XRD and EDS (energy dispersive spectrometer). The current-voltage curve indicates that the conversion efficiency and Jsc of the devices based on the ZnO nanowires with seed layer are higher than the ones without seed layer. Besides, the incident-photon-to-current conversion efficiency (IPCE) manifests that the devices based on the ZnO nanowires with seed layer reveals more efficient charge extraction over a large part of the visible spectrum (400-800 nm) compared to the ones without seed layer. However, we find that CH3NH3PbI3 film cannot fully cover on the TiO2/FTO/glass substrate when ZnO nanowires were too long. Therefore, the ZnO nanowires with seed layer prepared via a shorter-time hydrothermal process, the length of ZnO nanowires are shorter. When the time of the hydrothermal process is 1 hour, the cells based on which exhibit higher coverage of CH3NH3PbI3 film, Obtain higher photoelectric conversion efficiency.When the hydrothermal reaction time decreased from 4h to 1h, the efficiency was raised from 0.85% to 8.56%. Finally, we explored the possible reasons for the less common "s-shaped" curve in the current-voltage measurement.