双面受光铜铟镓硒太阳电池中扩散阻挡层的研究

Bifacial copper indium gallium selenide (CIGS) solar cell using transparent conducting oxide (TCO) back contacts enables us to get electrically illuminated light from both sides of the cell. So the utilization of the sun light will be effectively improved. However, the solar cell performance is deteriorated for higher deposition temperatures which are commonly used for CIGS deposition. This is attributed to diffusion of elements or chemical reaction at the interface region of TCO/CIGS which leads to the non-ohmic contact between the CIGS and TCO. In this project, in order to prevent the diffusion of elements or chemical reaction at the interface region of TCO/CIGS, we propose to develop an ultra-thin diffusion barrier between TCO and CIGS. The primary objective of this project is to establish quasi-ohmic contact between CIGS and TCO. We propose to study the metal-silicon-nitride layer as ultra-thin diffusion barrier to prevent the diffusion of elements and chemical reaction at the interface region. The interface structure, thermal stability, electrical properties, optical properties, interface band structure of TCO/diffusion barrier/CIGS and the effects on solar cell performance will be discussed on the basis of the characterization results from different characterization methods such as grazing incidence X-ray diffraction and photoelectron spectroscopy using synchrotron radiation. We propose to improve interface band structure of TCO/diffusion barrier/CIGS and enhance carrier extraction by regulating the structure and electrical properties of metal-silicon-nitride diffusion barrier. This research has significance to the development of bifacial thin film solar cells and high-efficiency tandem solar cells.

双面受光铜铟镓硒(CIGS)太阳电池采用透明导电氧化物（TCO）背电极，电池前后两面都可入射太阳光，充分提高了对太阳光的利用率。针对CIGS高温沉积过程中，TCO/CIGS的界面化学反应造成非欧姆接触、降低电池性能的具体科学问题，提出开展TCO背电极超薄扩散阻挡层的研究。本课题以实现TCO背电极与CIGS的准欧姆接触为核心目标，重点研究三元金属硅氮化物扩散阻挡层对TCO/CIGS界面元素互扩散和化学反应的抑制作用，采用同步辐射掠入射X射线衍射、同步辐射光电子能谱等表征手段，研究TCO/扩散阻挡层/CIGS的界面结构、热稳定性、电学性能、光学性能、界面能带结构及其对电池器件性能的影响机制。通过调控三元金属硅氮化物扩散阻挡层的结构和电学性能，优化TCO/扩散阻挡层/CIGS的界面能带结构，提高TCO背电极的载流子收集效率。研究成果对发展双面受光薄膜太阳电池及高效叠层太阳电池具有重要意义。

双面受光铜铟镓硒（CIGS）太阳电池具有充分吸光、超薄、适合于叠层电池的优点，是目前薄膜太阳电池研究的新领域。由于其采用透明导电氧化物（TCO）背电极，在CIGS高温沉积过程中，TCO/CIGS的界面会发生元素扩散和化学反应，从而造成非欧姆接触、降低电池性能，针对这些科学问题，我们开展了对TCO背电极扩散阻挡层的研究。我们系统地研究了扩散阻挡层的制备工艺，采用磁控溅射法成功制备出扩散阻挡层。我们对扩散阻挡层的薄膜结构、电学性能、光学性能以及界面物相进行了详细研究，获得了一系列研究成果。在此基础上，我们成功制备出双面受光CIGS电池，并优化了其制备工艺和器件性能，从器件性能角度研究了扩散阻挡层对双面受光CIGS电池的影响，发现扩散阻挡层有效地阻碍了界面元素扩散和化学反应，优化了光生载流子在CIGS和TCO层之间的输运过程，提高了电池效率。为了进一步降低吸收层制备过程中较高衬底温度对背电极造成的影响，我们详细研究了可替代CIGS作为双面受光电池吸收层的低熔点CuSbS2层及其太阳能电池，揭示了符合化学计量比的单一相CuSbS2薄膜形成条件，并得到了具有一定光电转换效率的器件。更进一步，我们研究了双面受光CIGS电池的其他各功能层：可作为背面窗口层的耐高温TCO层，可作为缓冲层的CdSxSe1-x层、可作为柔性双面电池背电极层的纳米复合材料电极等。我们研究了几种与双面受光CIGS电池的光谱覆盖范围互补、并能够与之组成叠层电池的电池单元，并得到了较好的光电转换效率，为今后进一步提高叠层太阳能电池的光电转换效率提供了一个可行的方向。