Study On TiO₂ Nanorod Arrays-based Solar Cells

New generation solar cells cause great attention and research interest of scientific researchers in recent years.One dimensional TiO₂ nanorods are easy to prepare,stable in performance,and friendly to the environment.Therefore,it is promising for TiO₂ nanorods as the electron transporting layer for solar cells.The hydrothermal method is used to prepare nanomaterials as well as TiO₂ nanorod arrays to build high-performance and low-cost organic-inorganic hybrid solar cells,relying on its advantages of controllable synthesis process and moderate reaction conditions.Orgainc/inorganic solar cells based on solution fabrication process has become an effective way to fully utilize solar energy,which may solve key issues such as energy shortages and environmental pollution.The preparation of nanomaterials and photovoltaic devices based on hydrothermal synthesis is the focus of this work.Hydrothermal method is used to synthesize Zn-doped FeS₂ powder.The obtained products are micro-spherical particles composed of many regular prismatic nano-slices with uniform size and relatively smooth surface.The innovation of this work is that we doped the ferrous disulfide materials to adjust their optoelectronic properties for the first time.In addition,the length of the TiO₂ nanorods can be effectively controlled by adjusting the reaction time and temperature.Before the hydrothermal reaction TiO₂ seed layer is formed,the resulting nanorods are grown in oriented direction and densely.Heterojunction formed by quantum dots decorated TiO₂ nanorods is helpful to transfer electrons at the interface.Moreover,alkali treatment of TiO₂ nanorods can effectively reduce the oxygen vacancy defect density on TiO₂ nanorod surface,which inhibited recombination of photogenerated carriers at the TiO₂/perovskite interface well.This thesis is divided into two parts:First,we used a modified two-step solution process to synthesis monodispersed Ag₂S quantum dots,which decorated hydrothermal TiO₂ nanorods uniformly and densely.Modified TiO₂ nanorods were used to be electric transporting materials for organic/inorganic hybrid solar cell.The characteristics of TiO₂ nanorods and their cells performance were investigated.Second,TiO₂ nanorods were synthesized by hydrothermal method,followed by alkaline treatment and annealing.Modified TiO₂ nanorods were used to be electric transporting materials for perovskite solar cell.The characteristics of TiO₂ nanorods and their cells performance were investigated.In the first section,core-shell shaped nanorod arrays with type-II band alignment heterojunction is a promising nanobuilding block for efficient charge transfer at the interface.Here in this work,we have fabricated Ag₂S quantum dots decoration on surface of vertically aligned TiO₂ nanorod arrays.A modified two-step solution process is used to obtain uniform Ag₂S quantum dots shell that promotes exciton dissociation at the organic/inorganic hybrid interface.Because of the enhanced charge tranfer,the photovoltaic conversion efficiency shows a drastic improvement of up to 73%for the solar cell adopting TiO₂/Ag₂S core/shell nanorod arrays as the electron acceptor.Therefore,the core-shell structure is a good electron transporting layer for photovoltaic devices.It is a promising nanostructure for core-shell nanorod arrays with cascaded type II heterojunctions,which is highly efficient as electron transporting layer.In the second section,weak ammonia was used to treat titanium dioxide nanorods synthesized based on hydrothermal method.Then the optimized nanorods were used as the electron transport layer of MAPbI₃ perovskite solar cells.The morphology and optical properties of the nanorods have shown that despite the alkali treatment,the morphology and arrangement of the modified nanorods have not changed significantly.Neither does it,s optical properties.In the device application,the current density of MAPbI₃perovskite solar cell based on TiO₂ nanorod arrays after alkali treatment was increased by 5%compared with that of the untreated device,and the efficiency was increased from 15.2%of the untreated device to16.6%of that after alkali treatment.We believe that the OH^-group provided by the weakly basic aqueous ammonia solution can fill the oxygen vacancies and the suspended titanium atom bonds on the surface of the TiO₂ nanorods.During high-temperature annealing,Ti-OH groups decompose to form Ti-O groups,which reduces the oxygen vacancy density.The performance improvement of MAPbI₃ perovskite solar cell based on modified TiO₂ nanorod arrays was ascribed to reduced defect states and enhanced interface charge separation.