Device Performance Study On Transparent Conductive Oxide Thin Films Used As Carrier Transport Layers In Perovskite Solar Cells

In the face of the current energy crisis and environmental pollution,solar energy,as a renewable energy source,is one of the important ways to meet the growing energy needs in the world.The research and development of high-efficiency and low-cost new solar cells is the technological foundation for the widespread application of solar photovoltaic power generation beyond silicon cells.Organic-inorganic hybrid perovskite solar cell（herein referred to perovskite solar cell）is a new type of all-solid-state thin-film solar cell.The photoelectric conversion efficiency has been increased to 22.7%,which has become one of the hot research topics in the field of renewable energy.In the thesis,the oxide film is used as the carrier transport layer of single-junction perovskite solar cell and the tunneling junction layer of monolithically-integrated tandem solar cells.Based on thin film growth technology optimization and regulation of transparent conductive properties,the main research focuses on the following four aspects:1.PLD growth of zinc oxide thin film and performance optimization of perovskite solar cells using ZnO as electron transport layer.By using the PLD growth method,the growth parameters（oxygen partial pressure）were optimized,and high-quality,high-transmittance,and conductive ZnO transparent films were obtained.The experimental results showed that by controlling the growth parameters of PLD,the physical properties of ZnO,such as the transparency and conductivity,can be precisely and repeatedly adjusted.This controllable adjustment cannot be accomplished by the solution method.Simultaneously,N-i-P planar heterojunction solar cells with ZnO thin films based on different oxygen pressures as electron transportlayers（ETL）wereconstructed.Thestructurewas FTO/ZnO/CH₃NH₃PbI_3-xCl_x/P3HT/Au.The performance of the solar cell is closely related to the transparent conductive properties of the ZnO film.When the ZnO thin film was grown at5 Pa as ETL,the best efficiency of the solar cell was 6.3%.However,the PCE of ZnO ETL-based devices is still lower than that of TiO₂ ETL-based solar cells.Mainly due to the inherent point defects and surface defect states of zinc oxide can cause serious recombination.The experimental results showed that solar cells based on ZnO thin films had poor stability and degrade rapidly in the case of 70 ⁰C annealing.In order to modify the interface between the ZnO electron transport layer and the perovskite absorber layer,a PCBM layer was introduced.After modification of the interface,perovskite solar cells exhibited higher PCE.This part of the study laid the foundation for the application of ZnO materials to transparent window layers,flexible devices,and tandem solar cell.2.PLD growth of inorganic NiO thin films and its optimization as a hole transport layer for high-performance perovskite cells.In order to eliminate the residual internal stress,reduce the defect state and improve the crystallinity,the NiO film prepared by the PLD method was post-annealed.The effect of post-annealing temperature on the growth of NiO film and the performance of the perovskite solar cell were systematically explored.After post-annealing,the surface of NiO film become more dense which can reduce the photocarrier recombination and effectively use solar radiation and its optical transmittance increase.Accordingly,the power conversion efficiency（PCE）of the perovskite solar cell improved from 5.38%to12.59%.In order to enhance its conductivity,the successful addition of lithium by PLD technology can effectively reduce the carrier transmission loss in the hole transport layer.Therefore,the PCE of the solar cell was further increased to 15.51%,and it has considerable long-term stability.3.Optical design and performance control of between SnO₂ tunneling junction and absorber layer of silicon/perovskite tandem solar cell.A single semiconductor material is too narrow compared to the solar spectrum,which fundamentally limits the improvement of efficiency.In order to further increase the utilization of solar energy spectrum and reduce the heat loss,different band gap perovskite cells and silicon heterojunction cells are connected in series to absorb and use the incident light in different wavelength ranges to obtain a high-efficiency solar cell.Here we report a low-temperature solution process for efficient perovskite/Si tandem solar cell.A highly-efficient perovskite/Si monolithic tandem cell formed by adjusting the electrical and optical properties of electron transport layer,as well as optimizing the bandgap and the thickness of perovskite absober to further realize current matching between the two sub-cells.With the optimized condition,the tandem cell with 1.69eV bandgap of the perovskite absorber delivers a power conversion efficiency（PCE）of22.22%.The steady state efficiency output at 1.42 V could reach over 20.6%after over 200 s illumination.The perovskite/Si two-terminal tandem devices retain more than 85%of its original efficiency after 500 h stability test.4.Optical design of magnesium fluoride anti-reflection layer in silicon/perovskite laminate cell and its effect on device performance.In order to reduce the loss of light reflected from the surface and further increase the photocurrent density,it is an important approach to adding the magnesium fluoride antireflection layer onto the silicon/perovskite tandem solar cell.Using the Finite-Difference Time-Domain（FDTD）method,the optical field simulation and analysis of the optimum thickness of the magnesium fluoride anti-reflection layer in monolithically-integrated PSC/Si tandem solar cell were performed.A silicon/perovskite tandem solar cell with anti-reflection layer was built by vacuum thermal evaporation.The short-circuit current density of the tandem cell increased by 1-2 mA/cm²,which further improved the efficiency of the tandem cell.Experimentally,a monolithically-integrated PSC/Si tandem solar cell with anti-reflection layer by vacuum thermal evaporation has been built,and the device efficiency and short-circuit current density have been improved to some extent.The experimental results were in good agreement with the theoretical simulations.The use of anti-reflection layer provides a new opportunity to further improve the utilization of sunlight and photoelectric conversion efficiency.