Effects Of PbI₂ And Electron Transport Layer On Device Performance In Perovskite Solar Cells

Meatl halide perovskite solar cells have attracted great attention in recent years,due to its high efficiency,low cost,and the ease to make.Although its photoelectric conversion efficiency has increased from the initial 3.8%to the current 25.7%,there is still a long way to go before its commercial application.To obtain efficient solar cells,it is crucial to optimize and improve the quality of the perovskite and carrier transport layers.In this thesis,the n-i-p planar-structure perovskite solar cells of ITO/SnO₂/FAMAPbI₃/Spiro-OMe TAD/Mo O₃/Ag were fabricated.The effects of thePbI₂ precursor on the properties of perovskite thin films and the performance of solar cells were investigated.Besides,the SnO₂ electron transport layer was modified by PVP to further improved the device performance.Some significant results have been obtained as following:1)The effects of PbI₂ precursor on the properties of perovskite thin films and the performance of solar cells were investigated.It was found that the concentration of PbI₂ precursor not only determines the proportion of PbI₂ in perovskite layer,but also affects its grain size,grain orientation and optical absorption,resulting in the changes in the performance of device.Furthermore,the morphology,crystallinity and porosity of PbI₂ are also significantly affected by the annealing method.Compared with the solvent annealing,the PbI₂ film prepared by short thermal annealing is more conducive to reducing the surface and interface defects of the perovskite fim and improving the open-circuit voltage.In addition,the solvent ratio of PbI₂ greatly affects the performance of PbI₂ films.When an appropriate amount of DMSO was introduced into pure DMF solvent,the quality of PbI₂ films were more uniform and the absorption of tailed defect states was reduced,which are beneficial to obtain high-quality,low-defect perovskite films and improve the open circuit voltage and fill factor of the devices.2)The commonly used SnO₂ electron transport layer is mostly commercial colloidal solution,which is easily uneven dispersion and leads to many film-forming particles and poor conductivity,and thus affects the performance of the device.On the other hand,in order to improve the wettability of the PbI₂ solution on the SnO₂surface,UV ozone pretreatment of the SnO₂ electron transport layer is usually required,which leads to the increase of defect states on the SnO₂ surface,resulting in poor charge transport and carrier recombination at the SnO₂/perovskite interface.Therefore,we explored the PVP-modified SnO₂ electron transport layer and its effect on the performance of solar cells.We found that adding a certain amount of PVP to the SnO₂ solution can improve the transmittance and conductivity of the film,while promoting the dispersion of SnO₂ and reducing its surface roughness,thus improving the short-circuit current and fill factor of the device.In addition,the introduction of PVP can effectively reduce the damage of SnO₂ by UV-ozone hydrophilic treatment.