Cu2ZnSn(S,Se)4的缺陷控制及其高效率薄膜太阳能电池研究

CuZnSn(S,Se)4 (CZTSSe) films are idea canditates for high-efficiency and cheap thin-film solar cells. Its efficiency is still relatively lower than that of Cu(In,Ga)Se2 thin-film solar cells and CZTSSe solar cells have a high open voltage deficit. Lattice defects ( severe band tailing caused by many shallow-level defects and defect clusters, and short minor carrier lifetime casued by deep-level defects) are mainly responsible for the open voltage deficit. How to reduce band tailing and increase the minor carrier lifetime by defect control, which is a key scientific question to reduce the open voltage deficit. Some studies have demonstrated that post-annealling, composition control and element doping are possibly three kinds of method to effectively control defects. However, their physical mechanism on specific defect control, and the effect of defect control on physical properties of CZTSSe and its solar cells, are unclear and need to study further. Therefore, we will study how to use three kinds of process method (i.e., post-annealling, composition control and element doping) to control lattice defects of CZTSSe thin films, so as to understand the effect of defect control on the optical and electrical properties of CZTSSe and its solar cells. Develop the fabrication method of high efficiency (> 10%) CZTSSe thin-film solar cells, based on the above research results.

铜锌锡硫硒Cu2ZnSn(S,Se)4(记为CZTSSe）薄膜是高效率廉价薄膜太阳能电池的理想候选材料，但与铜铟镓硒薄膜电池相比，CZTSSe电池的效率还相对较低，主要表现在电池开路电压损失较大。晶格缺陷（大量浅能级缺陷和缺陷簇引起的严重带尾态和深能级缺陷导致的低少子寿命）是限制开路电压的最重要的影响因素。如何通过控制缺陷来降低带尾态和提高少子寿命，是减少开路电压损失的一个关键科学问题。现有研究表明：退火工艺，组分调控和元素掺杂可能是控制缺陷的三种有效方法，但它们控制具体缺陷的物理机制、及其对CZTSSe的光电性质和电池性能的影响尚不清楚，亟待研究。本项目拟研究三种工艺手段（退火工艺，组分调控和元素掺杂）控制CZTSSe晶格缺陷的科学规律，揭示缺陷控制对CZTSSe薄膜光电性质和电池性能的影响机制，发展高效率（>10 %)CZTSSe薄膜太阳能电池制备技术。

限制铜锌锡硫（CZTS）薄膜太阳能电池效率提高的关键因素之一是开路电压偏低。CZTS具有严重带尾态缺陷，这是其开路电压较低的重要原因。针对这个关键科学问题，本项目主要在CZTS的大晶粒生长、缺陷控制机理和铜锌锡硫硒（CZTSSe）高效率太阳能电池研制三方面开展了系统深入的研究，取得了如下阶段性的研究成果。第一，发展了分层溅射金属层后硫化工艺制备高质量、大晶粒CZTS薄膜的工艺方法，首次阐明了在该工艺下CZTS大晶粒生长的物理化学机制，这为深入开展缺陷研究和制备高效率电池提供了材料保障。第二，综合利用多种半导体光谱技术，结合理论计算分析，确认了[2CuZn+SnZn]缺陷簇是CZTS带尾态的主要起源。在此基础上，首次从实验上揭示了贫Sn减小CZTS带尾态和深能级缺陷的物理规律，这为利用组分调控实现CZTS缺陷控制的方法提供了新的科学依据。第三，探索和优化了CZTSSe电池的工艺技术，制备了转换效率超过11%（全面积10.3%）的CZTSSe薄膜太阳能电池器件。围绕上述部分学术成果，项目主持人在J. Phys. Chem. Lett.，Solar Energy，J. Alloys Compds. 等国际SCI期刊上发表12篇学术论文，其中以通讯作者身份发表9篇，合作者身份3篇。针对CZTS薄膜电池制备工艺方法，申请了国家发明专利1项，已授权。