基于氧化物纳米线三维异质结材料太阳能电池的基本问题研究

In this proposal, we plan to construct low-cost, high efficiency 3 dimensional heterojunction solar cells by combining n-type oxide (ZnO, TiO2) nanowire arrays with p-type copper-based semiconductors (CIGS, CIS, Cu2O, etc.); Relevant physical principles and technique issues in the development of 3 dimensional heterojunction solar cells, such as materials growth, energy band engineering, charge separation and transport, interfacial defects passivation, and device stability, will be investigated theoretically and experimentally. The harvest efficiency of solar cells can be greatly enhanced by nano-scale light trapping configuration which comes from the big difference of refractive index between oxide and copper based semiconductor, and band-gap engineering of composition-graded 3D heterojunctions. Though heterojunction interface engineering, interfacial electron-hole recombination rate will be reduced effectively and the device efficiency and stability can be improved. An energy band model of 3D heterojunction solar cell will be established in order to elucidate the mechanism of charge separation, recombination and transportation. The proposed study will collect key factors for 3D heterojunction solar cell designation and optimization from the aspects of material engineering, physics, chemistry and nanotechnology. We will fabricate and evaluate our high efficiency 3D heterojunction solar cells, which can provide scientific evidences and technical bases for the realization of large scale application of thin film solar cells.

本课题以n-型氧化物纳米线阵列和p-型Cu系半导体构建高效率、低成本的三维异质结太阳能电池器件为目标，将针对三维异质结太阳能电池制备过程中涉及到的材料生长、能带结构设计、电荷分离和输运、缺陷钝化和器件稳定性等基本问题开展研究工作。通过构建微纳尺度的陷光结构和组分渐变的三维异质结，提高太阳能电池的光吸收率和光谱覆盖范围；通过界面工程，探寻降低界面复合速率、提高器件光电转换效率和稳定性的途径；通过构建三维异质结太阳能电池的能带结构模型，揭示三维异质结太阳能电池中光生电荷的分离、复合和输运机理。从材料、物理、化学多学科角度获得高效率三维异质结太阳能电池结构设计和性能优化的关键信息，揭示三维异质结的微纳结构和界面性质影响器件光伏性能的基本规律，为实现高效的固态三维异质结太阳能电池奠定基础。

本项目聚焦氧化物纳米线基三维异质结器件，通过构造微纳结构的三维异质结将光吸收和光生载流子收集方向正交化，以破解传统平面异质结型太阳能电池难以平衡光吸收和电荷收集的难题。项目从材料选择和三维异质结构造、异质结界面调控、载流子相关过程等多个角度开展研究。系统考察了氧化物纳米线阵列与多种p型光吸收材料（铜系半导体、硫化铅量子点、有机无机杂化钙钛矿）构造的三维异质结器件性能及其对微纳结构的依赖性；探索了利用界面工程手段抑制三维异质结界面电荷复合；利用空穴收集层进一步提高器件电荷收集效率；在此基础上进一步开展了柔性三维异质结器件、新型透明导电薄膜和柔性电极材料、陷光结构构造、自供电光电化学水分解系统等研究工作。取得了如下重要结果：（1）利用溶液沉积方法制备的氧化物（ZnO、TiO2）纳米线阵列与铜系半导体材料（Cu2O、Cu2ZnSnS4）、PbS量子点、CH3NH3PbI3钙钛矿等结合，构建三维异质结器件，发现PbS量子点与ZnO纳米线是构造三维异质结器件的最优组合，优化器件微纳结构和制备工艺获得了光电转换效率7.93%，空气稳定性>6个月的ZnO纳米线/PbS量子点三维异质结太阳能电池。与之相比，p-型铜系材料的高温制备条件易引起异质结界面劣化，钙钛矿材料反应过程的体积膨胀导致氧化物纳米线填充难以控制。（2）利用界面工程手段抑制三维异质结界面复合。在ZnO纳米线与PbS量子点界面引入Mg(OH)2超薄界面层，有效钝化ZnO表面缺陷态、抑制载流子的反向界面复合，将器件开路电压提升33%，功率转换效率提升25%。（3）首次获得了三维异质结构的柔性ZnO/PbS量子点太阳能电池，利用ZnO纳米线阵列的弯折应力释放作用大幅度提升PbS量子点太阳能电池的抗弯折性，使该柔性电池160o弯折角度下机械弯折100次，功率转换效率仍能保持原来的93%。本项目研究结果对于深刻理解微纳结构光电器件及其物理具有重要的参考价值，为研发基于微纳结构的低成本高效率太阳能电池提供了科学依据和技术基础。