基于高效双异质结氧化物光伏器件的载流子输运性能调控研究

To fundamentally promote the conversion efficiency of all-oxide thin film photovoltaic devices, the energy band matched double heterojunction device TiO2(n+)/CuO(p)/CuFeO2(p+) of wide optical absorption region and high efficiency is put forward on the ground of theoretical study. Electron transport performance of the device is promoted by utilizing Nb-TiO2 with significantly improved conductivity as the window layer. Trough employing CuO as light absorption layer together with the double heterojunction design, the photovoltaic cells would have the ability to absorb solar light with various wavelength regions, which thereby will depress the energy lose caused by intra-band relaxation of high energy electrons excited by high energy photons, and give out high photocurrent density. Double heterojunction design by using CuFeO2 to adjust built-in electric field, can efficiently promote the open circuit voltage of the devices. The valence band of CuFeO2 thin film can be modified through acceptor elements doping, and thus its optical and electronic performance such as hole concentration and mobility can be coordinately controlled..In this project, the research will focus on the followings: (1) the mechanism of Mg, Ca acceptor dopants and oxygen defects on the band structure and carrier performance of CuFeO2 film; (2) the contact property between doped CuFeO2 film and back contact metal electrode, for the purpose to obtain ohmic contact of low contact resistance. On the basis of these, double heterojunction oxide photovoltaic devices will be fabricated under theoretical guidance and the influence of materials and structure on the carrier transport property, built-in electric field in space as well as the photo-electric performance of devices will be studied in depth.

针对全氧化物薄膜光伏器件转换效率低的问题，依据理论研究提出能带匹配的高效率新型宽光谱双异质结TiO2(n+)/CuO(p)/CuFeO2(p+)器件结构。采用Nb-TiO2作为窗口层，改善电子传输性能；CuO作为光吸收层，多层结构设计，实现多波段光谱吸收，减少高能电子在能带中的弛豫，增加光生载流子浓度；双异质结设计，CuFeO2层调节内建电场分布，增加开路电压，利用受主元素掺杂对CuFeO2进行价带修饰，调节空穴浓度和迁移率，增强空穴传输性能。本研究主要解决如下关键问题：(1) 深入研究Mg、Ca受主掺杂和氧缺陷对CuFeO2薄膜能带结构与载流子性能的作用机理，实现对其光电性能协同调控；(2) 揭示掺杂CuFeO2薄膜与金属背电极的接触特性，以获得欧姆接触，降低接触电阻。组装双异质结全氧化物光伏器件，研究电池结构、材料性能、载流子输运性与内建电场分布、光电转换性能的关联，提高电池转换效率。

利用元素掺杂对p型铜铁矿结构CuFeO2进行价带修饰，有效调节空穴传输性能，是CuFeO2材料用于光电领域的关键。本项目通过系统研究氧缺陷、掺杂元素包括N、Ca、Zn、Mg、Ni对空穴传输材料CuFeO2能带结构、光电性能、与金属电极接触特性的影响等，揭示了氧缺陷、元素掺杂对能带结构和光电性能的影响，实现了对CuFeO2能带结构、载流子浓度和迁移率的有效调控。所制备的CuFeO2空穴浓度在1017-1020cm-3之间，与金属Cu形成良好欧姆接触。通过研究TiO2/CuO/CuFeO2光伏器件中光生载流子的分离和输运过程，阐述CuFeO2用于光伏器件的载流子传输机理，获得优化结构，器件最高理论光电转换效率高达28%以上。本项目研究为探索无机氧化物半导体光电器件的应用提供了理论和实验基础。依据该研究基础，对相关类型太阳能电池中载流子传输特性和光电性能展开了研究，包括以TiO2、ZnO、CdS为电子传输层的钙钛矿太阳能电池，硅化物太阳能电池，MoS2太阳能电池等，共发表论文9篇。