Interfacial Engineering For High Performance Perovskite Solar Cells

Hybrid organic-inorganic metal halide perovskite materials possess combined advantages of strong light absorption,long charge carrier diffusion lengths,and widely-tunable band gap,which bring remarkable optoelectronic performance.In addition,it can be prepared at a low-temperature in a low-cost solution process,giving it great commercial potential.Since the Japanese scientists Tsutomu Miyasaka et al.applied perovskite materials in dye-sensitized solar cells(DSSC)for the first time in 2009,scientists have made lots of breakthroughs over the past decade.The perovskite solar cells developed rapidly with a fast ramping of the power conversion efficiency from the initial 3.8%to the current 24.2%,which is approaching to the theoretical limit efficiency(31%)of PSCs.At the same time of these great progress,there are still many problems such as the unclear working mechanism,the complicated preparation process,and the low stability of the perovskite materials.In order to solve these problems,we start from the important interface in the cells.Through the improvement of the device preparation process and materials,we study the better process and device structures,and improve the power conversion efficiency of the PSCs.Also,the working mechanism of the semiconductor device is investigated from the perspective of physics.The content of our research can be divided into the following sections:(1)A novel device structure is designed to reduce the manufacturing process cost and complexity of the solar cells.The new preparation process produces high performance solar cells by introducing the organic bulk-heterojunction into the interface between the perovskite and hole-transporting layer.The organic bulk-heterojunction increases light absorption of the device,passivates the interface,reduces the density of the defect states and promotes the transportation and extraction of carriers,which makes the solar cells to present a high power conversion efficiency around 20%.The stability of the cell is also improved by increasing the hydrophobicity of the interface.The research result leads to a new possibility of exploring the large-scale industrial production of perovskite solar cells.(2)A novel transparent conductive oxide(TCO)Gallium Oxide(Ga2O3)nanocrystalline film is applied as an electron-transporting layer based on the idea of optimizing the traditional n-i-p structure device.Gallium Oxide has higher mobility and higher optical transmittance than TiO2.The Gallium Oxide nanocrystalline film prepared by the solution process is smooth and induce the growth of a denser perovskite film.By optimizing and controlling the preparation of Gallium Oxide nanocrystalline film,it is expected to completely replace TiO2,and to further improve the PCE and stability of the n-i-p structure solar cells.(3)We found that the crystallization of the perovskite functional layer is an important factor affecting the performance of solar cells based on our previous research.With the help of synchrotron radiation technique,we use Grazing Incidence X-ray Diffraction(GIXRD)to characterize and analyze the film orientation of the perovskite film and establish a connection with the device performance.In summary,this thesis tries to find a way to further improve the performance and stability of the perovskite solar cells by designing new device structures and introducing new materials.Through the more detailed characterization of the morphology and the crystallization of the perovskite films,we propose a mechanism explanation to the efficiency of the solar cells.This also provides a theoretical basis for designing better solar cell materials and devices.