基于宽带隙、强各向异性硫化锑的高效平面结薄膜太阳能电池研究

Antimony sulfide holds unique advantages such as suitable bandgap, high absorption coefficient, simple binary phase, non-toxic and low cost, etc., which make it high potential as top-cell candidate for silicon tandem solar cells. The present research of efficient antimony sulfide solar cells meets the research requirement of high efficiency top-cell for silicon tandem solar cells as the crystalline silicon photovoltaics are approaching single junction Shockley-Queisser (SQ) limit. The implementation of present proposal will make it possible for efficiency breakthrough of Silicon solar cells. The key problem for antimony sulfide solar cells is its relatively low conversion efficiency, which are originated from low transport mobility induced by strong anisotropy, high interface recombination velocity led by defects, reverse diode at back contact resulted from deep work function and low carrier concentration. Our group has achieved stable and relatively high efficiency Sb2S3 planar solar cells. According to above rich experience, we plan to utilize modified rapid-thermal-evaporation method (mRTE), assisted with vapor-transport deposition (VTD) and hot wall epitaxy (HWE) to deposit large-grain Sb2S3 compact film. Then we will adopt buffer layer selected facets or seed layer for latter Sb2S3 guiding deposition. We further diagnose device defect and efficiently passivate it to improve junction quality. For Sb2S3 device back contact, we plan to utilize plasma enhanced chemical vapor deposition (PECVD) method to strengthen the anion concentration for selenium or tellurium substitution so as to implement ohmic back contact. We will combine all the functional layer optimization to improve device performance. We try to implement stable, certified 10% Sb2S3 solar cells, obtain creative wide-bandgap top-cell strategies and techniques. Therefore, the present research proposal is expected to provide theoretical and technical support for next-generation photovoltaic development.

硫化锑因具有1.72eV禁带宽度，高的吸光系数，二元简单物相，无毒和低成本等本征优势而成为硅基叠层电池顶电池极具潜力候选体系。对应其高效电池研究迎合了当前亟需发展宽带隙高效顶电池技术的研究趋势，以解决硅基电池效率（硅基单结电池已逼近理论极限）跨越式发展问题。为克服强各向异性引起的迁移率低，缺陷导致的界面复合速率大，深功函、低载流子浓度导致的反向背结等瓶颈问题，课题基于前期丰富的平面结电池基础，拟采用改进型闪蒸法（mRTE）辅以气相输运沉积（VTD）和热壁外延（HWE）等新工艺沉积大晶膜；利用缓冲层晶面、籽晶诱导技术调控晶体直立取向；以界面缺陷的物理诊断和钝化提升结质量；针对性利用PECVD的等离子体增强调制背面同族阴离子合金化新策略以提升空穴抽取效率。经各层协同优化，预期实现稳定、认证的10%光电转换效率。本项目的实施将获得新型宽带隙高效电池工艺和技术，为下一代光伏发展提供理论与技术支持。

本项目针对当前单结太阳电池光电转换效率逐渐逼近其极限而亟需发展下一代叠层太阳电池技术。项目组在项目高效硫化锑薄膜太阳电池的研究目标指导下，重点围绕硫化锑平面结太阳电池界面复合速率大，吸收层体缺陷密度高，器件空穴抽取效率低等代表性关键科学问题，开展了PN界面、体薄膜质量、空穴抽取效率系列研究工作。在PN界面质量提升工作方面，项目组开发了系列兼顾高质量PN界面和体薄膜质量的硫化锑沉积方法，透彻理解了硫化锑异质基底生长的关键因素。首次实现了硫化锑在惰性TiO2基底的准外延高温气相沉积方法和无中间过渡层的低温水浴沉积技术，高效地降低了界面缺陷浓度；在体薄膜质量提升方面，理论模拟和实验验证了硫化锑低温水浴生长过程的缺陷形成过程的抑制方法-多源离子共掺杂策略，研究结果表明其体缺陷浓度降低一个量级，少子寿命提高2倍；针对强各向异性特性，从设备、直立取向调制工艺以及硫化锑生长模型等方面建立了一条线式创新，开发了新的垂直型气相输运沉积设备（V-VTD），实现了硫化锑的直立取向沉积；在硫化锑太阳电池的空穴抽取效率提升上，分别重点突破后表面薄膜的阴离子、阳离子合金化，掌握了近本征硫化锑合金化提升掺杂浓度策略，实现硫化锑太阳电池的空穴高效抽取。在项目组系列创新成果基础上，项目组针对硫化锑太阳电池各功能层、性能提升、未来挑战和展望进行了系统的梳理和总结。成功研制出效率达到7.5%平面结硫化锑太阳电池，认证效率7.15%，为同期该类器件认证效率记录。在本项目资助期间，项目组发表20篇SCI论文，申请或授权发明专利8件，培养硕博士研究生10名，在读4名。对应成果获得2019湖北省自然科学奖二等奖以及2022年中国电子学会科学技术奖自然科学二等奖；研制的宽带隙硫化锑太阳电池为未来高效叠层太阳电池顶电池研究提供重要研究参考，有望促进相关领域的科学发展。