宽光谱氧化物太阳电池的关键材料挑战及器件研究

The current photovoltaic solar cells based on crystalline silicon are too expensive and alternative technologies also have their shortcomings for being based on materials of depleting resources or materials being toxic to environment (e.g. CuInGaSe、CdTe, CdS). This project aims at filling the present technological vaccum through developing a new class of low-cost solar cells through band-engineered TiO2. Under the guidance of extenisve mateirals/device modelling, we focus on achieving gigantic reduction of the TiO2 band gap via doping/alloying, thus offering a solid materials basis for the realisation of a novel WAV solar cell architecture, wherein the doped/alloyed TiO2 with graded band gap reduction allows PV energy conversion of a wide range of solar irradiance with little loss due to intraband relaxation from high energy photons. The incorporation of the low-gap CuO in the absorption component is to make up possible limitation in reducing the TiO2 band gap with limited defects. The novel Window-Absorber-Voltage enhancer cell design makes it viable to achieve high short-circuit current together with a large open-circuit voltage, leading to highly enhanced efficiency. The success of this project will lead to transformative advancement in offering a truly sustainable thin film PV solution, which is cheap, efficient and friendly to environment, thus opening a wide range of opportunities for China to lead the PV technology.

针对现有Si太阳电池价格昂贵及其替代体系(CuInGaSe、CdTe及CdS等)资源匮乏甚至毒化环境等突出问题，本项目基于TiO2的能带工程（掺杂/合金化），将其与窄带p型CuO相结合，旨在为下一代光伏电池提供全新的、环境友好的、可持续性的材料体系，并在此基础上开发新型宽谱吸收的高效太阳电池。期望通过掺杂及共掺技术，将TiO2的吸收带边从紫外波段大幅红移至可见光甚至近红外区域，以充分利用太阳光谱中的大部分能量。通过对TiO2吸收层带隙由宽及窄的连续调控，有效克服高能导带电子在带内弛豫引起的能量损失，实现对紫外到近红外广谱范围太阳光的无弛豫光电转换,利用窄带隙CuO作为长波吸光层，以补充TiO2带隙调制的可能局限，最终制备出新型全光谱吸收的高效（大于15%）示范太阳电池。本项目的实施，将为新型TiO2宽光谱太阳电池的发展奠定坚实的理论与实验基础，为新一代高效低成本太阳电池的发展开辟崭新道.

项目执行期间，研究了宽光谱氧化物太阳电池关键材料挑战及器件。1）基于第一性原理密度泛函理论，调控TiO2能带结构，通过合金化或掺杂元素可将带隙至少降低50%；适度掺杂可调控其导电类型，并获得合适的载流子浓度和高迁移率。2）系统模拟基于全氧化物的异质结和肖特基结电池，进一步研究缺陷与界面态对电池性能影响。理论效率高达28.6%。3）薄膜制备工艺及其质量制约氧化物电池发展，采用HiTUS镀膜技术，可实现过程高度可控，具有靶材利用率>90%和低温柔性衬底沉积的特点。4）系统研究能带渐变TiO2，制备可见光响应增强的Mn、Fe、V-Ga、Cu、Nb掺杂TiO2，成功将基于TiO2的多层结构应用于可见光催化降解污染物、可见光分解水制氢、及染料敏化、钙钛矿和氧化物太阳能电池，光电转换效率最高10.88%。5）采用HiTUS制备吸收层CuOx薄膜，实现薄膜晶型可控，载流子浓度在（10^14-10^19）cm-3可控，空穴迁移率达到12.3 cm2V-1s-1，且在金属-半导体结构中有良好的接触特性。研究缺陷、晶界、界面调制及热处理对薄膜的影响。6）研究无铟TCO薄膜，获得电阻率低于10-4 Ω•cm的NTO薄膜，透光率90%；获得电阻率低于10-3 Ω•cm的柔性Nb掺杂SnO2薄膜，透光率90%。7）研究过程中提出新思路，开展WAV结构器件的反向制备及优化；基于铜氧化物可控制备，提出全铜氧化物WAV电池；基于HiTUS技术，开展示范性薄膜沉积设备的研究和推广。此期间，发表国际刊物论文13篇，获得国家发明专利授权9项。