高Ga组分CIGS薄膜的晶体生长机理及突破其光伏器件电压瓶颈的探索研究

CuInGaSe2 (CIGS) solar cells is one of the attractive photovoltaic (PV) technologies for flexible portable power source and building integrated photovoltaics (BIPV). However, there is big gap between the record efficiency and its efficiency limit 32%, due to bottle neck of the open circuit voltage (Voc) increase in high Ga content CIGS. With increasing Ga content in the CIGS, the grain size of CIGS reduces, and thus the recombination in the grains and grain boundaries increase, resulting in significant reduce in Voc and efficiency. Recent, we have improved the Voc and current collection length of the high Ga content CIGS solar cells by reducing its thickness to sub-micrometer. We also found that the efficiency of the ultra-thin high-Ga content CIGS solar cell can be improved to 25% by reducing the back interface recombination. However, the impacts of the reduced thickness and interface kinetics on the performance of the high-Ga content CIGS are still unknown. Thus, the focuses of this research are: (1) the mechanism of the crystal growth of ultra-thin high-Ga content CIGS polycrystalline film, (2) Voc improvement mechanism of grain boundary passivation by heavy alkali element doping, and (3) the mechanics of short circuit current (Jsc) improvement of back interface passivation of ultra-thin high-Ga content CIGS. The key issues in fabricating high-Ga content CIGS solar cell will be elaborated, which will be helpful for new record efficiency of CIGS solar cells.

铜铟镓硒（CIGS）薄膜太阳能电池被认为是柔性移动能源、建筑光伏幕墙等应用场景的理想光伏技术，具有广阔发展前景，但受限于高镓组分CIGS电池中开路电压的提升瓶颈，其器件转化效率距离极限效率32%还有极大差距。高镓组分材料中，一个突出的挑战就是晶粒细化现象以及相应的晶界面载流子复合问题。我们的实验发现，晶粒细化的难题可以通过优化吸收层厚度和富铜退火得以解决，并成功突破了开路电压提升的瓶颈。本项目拟在此基础上进一步开展以下研究：（1）利用超薄结构和富铜退火促进晶体生长的机理和提高器件开路电压的机制研究，（2）高镓CIGS薄膜的重碱金属（铷和铯)后处理方案探索及其表面相的化学和电子态研究，（3）超薄吸收层器件的背电极界面钝化设计和短路电流提升途径研究。本项目的完成，不但有希望突破CIGS太阳能电池的开路电压和效率提升瓶颈，而且对于减少吸收层的厚度和降低In元素的使用等方面都带来新的思路。

针对目前高Ga组分CIGS太阳能电池的存在的关键问题：高镓组分CIGS太阳能电压提升瓶颈限制了其效率的进一步提高。该项目的实施有效推进了高Ga组分CIGS薄膜太阳能电池的研究，主要的研究内容和成果包括：1）利用减薄吸收层的策略，仅1.6μm厚的CIGS吸收层获得16.3％的光电转换效率器件，短路电流提高到≥31.4mA/cm2，开路电压762mV，基本完成研究目标。2）改善高Ga组分CIGS太阳能电池中Ga在背部聚集以及重碱金属后处理，获得了电池效率高达21.7%的器件，通过进一步增加减反层，效率可接近23%，纯Ga电池开路电压接近900mV，基本完成研究目标；3）利用SCAPS模拟，在背电极与吸收层直接增加MoO3，V2O5，WO3，CrO3和Co3O4等过渡金属氧化物，在使用亚微米厚的宽禁带CIGS（Eg=1.4 eV）吸收层，可以获得效率高达24%的电池，Voc和FF分别高于900mV和75%，完成研究目标；4）基于该项目发表SCI论文11篇，包括ACS Applied Energy Materials, Solar Energy, Composites Communications, Materials Today Energy等国际高水平SCI期刊，其中Solar Energy 195 (2020), 340-354入选ESI高被引论文，参加国际学术会议2次，申请国家发明专利7项。5）通过该项目的有效实施，将我国在高Ga组分CIGS太阳能电池的研究推进到了国际领先水平。