基于TiN/ITiO双功能窗口层的异质结太阳电池光电增强机理研究

The open-circuit voltage of silicon heterojunction solar cell exceeds 750 mV, which is close to the theoretical limit. However, due to the parasitic absorption and recombination loss of the window layer material, the further improvement of the photoelectric conversion efficiency is limited by the photocurrent density. This project has proposed the dual-function TiN/ITiO (titanium nitride/titanium-doped indium oxide) stacks, which is applied for the rear emitter solar cell to form high light transmittance, high conductance and carrier selective transmission window layer. This project will explore the interface photoelectric conduction mechanism and interface recombination/passivation contact mechanism by means of numerical simulation, material characterization and photoelectric performance optimization. The mechanism of electron-conductive and hole-blocking of TiN/ITiO window layer will be analyzed by establishing the photoelectric theory model of the device combined with the material properties, band structure and carrier transport, aiming at low recombination, low contact resistance and hole blocking passivation contact on light-doped n-type silicon film interface. The relationship between the material properties of TiN/ITiO window layer and the photoelectric enhancement of heterojunction solar cell and its physical mechanism will be discussed. The formation of TiN/ITiO stacks with excellent optical and electrical properties provide key theoretical support and reference for industrial application of heterojunction solar cell devices.

晶硅异质结太阳电池的开路电压达750 mV，接近理论极限，但由于窗口层材料的寄生吸收和复合损失，光电转换效率的进一步提升受限于较低的光生电流密度。本项目以背发射极结构为切入点，提出TiN/ITiO（氮化钛/掺钛氧化铟）双功能层，构建兼具高透光性、高电导和载流子选择性接触的太阳电池窗口层。研究将从数值模拟、材料制备和光电性能优化三个方面，探究TiN/ITiO窗口层的界面光电传导机制和界面复合/钝化接触机制。通过研究窗口层薄膜的材料特性、能带结构与载流子传输，建立器件光电理论模型，系统剖析TiN薄膜实现光伏器件电子传输、空穴反射的机理。结合器件制备，解决在轻掺杂的n型硅薄膜界面实现低复合速率、低接触电阻、高空穴反射的选择性钝化接触的难题，探讨窗口层材料特性与太阳电池光电增强的关系及蕴含的物理机理，实现高光生电流和优异钝化接触的光伏器件，为推动异质结太阳电池产业化应用提供关键理论支撑。

异质结太阳电池是目前最具有发展前景的晶硅太阳电池之一，目前规划产能超过100GW，实验室转换效率达到了26.81%。通过优化透明导电薄膜和n型掺杂层之间的接触，有望进一步提高太阳电池的性能。本项目提出TiN/ITiO（氮化钛/掺钛氧化铟）双功能层，构建兼具高透光性、高电导和载流子选择性接触的太阳电池窗口层。利用Afors-Het软件对太阳电池进行了模拟，研究了TCO功函数和电子选择性传输层对太阳电池性能影响。其次采用高真空反应磁控溅射技术制备TiN薄膜，对不同沉积条件下制备的TiN薄膜进行电学性能、晶体结构、光学特性等表征，分析了TiN薄膜沉积工艺和薄膜组成成分与电导率之间的关系。在0.4 Pa沉积压强下制备出高电导率（4000 S·cm-1）的TiN薄膜，具有7E21 cm-3的高电子浓度，电子迁移率为4 cm2·V-1·s-1。最后创新性地将TiN用于改善太阳电池中Ag和掺杂层之间的接触，通过场发射透射电镜在亚纳米尺度上观察到了掺杂层/TiN界面的微观结构。利用传输线法测试了Ag电极和TiN分别与掺杂层的接触电阻，发现插入一层超薄TiN薄膜能够降低界面接触电阻，使得器件串联电阻降低0.06-0.16 Ω·cm2，填充因子（FF）因此提高约1%。由于过厚的TiN会降低短路电流，未来通过TiN沉积工艺和材料性能的优化，有望实现既改善界面接触，又不影响短路电流，从而实现在高效太阳电池的应用，为推动异质结太阳电池产业化应用提供关键理论支撑和导向参考。