ZnTe:O基中间带光伏材料外延及异质结构设计

The development of novel high efficient photovoltaic cells is to strive for the goal to solve the existing energy crisis. The project aims at developing the intermediate band solar cells (IBSC) in which the highly mismatch alloy ZnTe:O acts as the absorbing layer. This alloys system has great potentials to realize the promise of high photon-electron conversion efficiency because of its unique absorption property, relatively simple structure and low cost. The project will conduct the systematic research on some key scientific issues and technical difficulties currently existing in ZnTe:O IB photovoltaic materials, including the aspects of electronic bandstructure engineering, high quality materials epitaxy, and device fabrication. The research will focus on developing high quality ZnTe:O IB materials on the large mismatched substrate and on controlling the oxygen composition beyond its solid solubility limit through low-temperature non-equilibrium growth and auxiliary means of ion implantation. In addition to the oxygen content, the project intends to develop ZnMgTe:O quaternary alloys to ensure large room for optimizing IB energy level positions and electron occupation status and thus to expand the absorption spectrum without sacrificing the open-circuit voltage.Based on the optimal epitaxy of materials, the project will design and fabricate ZnTe:O based prototype solar cell, identifying the electronic band structure, the dynamic processes of photo-genereted carriers in IB materials and establishing the physical correlation between device performance and material properties by means of different characterization, including photoreflectance, time-resolved photoluminescence and temperature-dependent Hall effect measurements. The thorough research efforts will serve as the solid basis theoretically and experimentally for the further development of high efficient and practical ZnTe:O based intermediate band solar cell.

发展新型高效光伏电池是人们为解决能源危机而努力追求的目标。本申请项目将新颖ZnTe:O基中间带光伏材料和异质结构能带剪裁相结合，提高低能光子的吸收效率和电子-空穴的空间分离，拟发展全光谱型的高效ZnTe:O基中间带光伏电池。本项目将围绕中间带电子能带调控、材料异质结构外延及器件工艺优化等关键科学问题开展系统研究，重点发展利用MOCVD实现高质量ZnTe:O中间带材料的非平衡生长技术，并以离子注入作为辅助手段，解决氧在ZnTe中固溶度低的技术难点。通过引入Mg组分拓宽氧对ZnMgTe中间能带结构的调控，提高宽谱太阳光的吸收效率，并利用能带剪裁增强内建电场，延长载流子寿命和提高原型器件的光电转换效率。利用光调制反射谱、时间分辨光致发光谱和电学测试等手段研究电子能带结构、载流子复合机制和输运特性，建立器件性能参数与材料结构相关联的物理模型，为进一步发展高效实用的中间带光伏电池奠定基础。

发展新型高效光伏电池是人们为解决能源危机而努力追求的目标。本项目将新颖ZnTe:O 基中间带光伏材料和异质结构能带剪裁相结合，提高低能光子的吸收效率和电子-空穴的空间分离，发展全光谱型的高效ZnTe:O 基中间带光伏电池。本项目首先基于密度泛函理论采用第一性原理理论揭示了中间带电子能带结构，并预测形成中间带特性所具备的掺杂条件；采用MOCVD方法实现了高质量ZnTe:O 中间带材料的非平衡生长，并通过后退火优化工艺，在提高氧掺杂效率的同时减小缺陷密度，降低非辐射复合中心，使得中间带电子态由局域态向扩展态过渡，从而提高整体材料的发光量子效率。同时项目采用离子注入和激光熔融方法相结合获得了高品质的ZnTe:O合金，解决氧在ZnTe 中固溶度低的技术难点。深入研究了激光熔融退火导致的微观结构、光学特征，利用时间分辨光致发光谱和电学测试等手段研究电子能带结构、载流子复合机制和输运特性；成功制备出具有中间带的ZnTe/ZnTeO/ZnO原型异质结电池结构，器件的室温光电导测试显示ZnTe/ZnTeO/ZnO在1.8eV和2.25eV处形成明显的光电导现象，而在ZnTe/ZnO结构中并未观察到1.8eV的光电导，进一步证实了之前关于中间带形成的判断。ZnTe/ZnTeO/ZnO的光电转换效率相比ZnTe/ZnO异质结构有较大提高，为进一步发展高效实用的中间带光伏电池奠定基础。