强耦合高效GeSi量子点中间能带光伏材料的制备及其光电特性研究

Semiconductor quantum dot (QD) is a highly efficient photovoltaic material for intermediate-band solar cells (IBSCs). However, the promise of high-efficiency QD-IBSCs has not been realized due to the low density, poor distribution and crystal defect of QDs. These disadvantages greatly weaken the coupling effect between QDs, hindering the formation of intermediate band. These led to a poor performance of QD-IBSCs with weak absorption, short-circuit current drop and open-circuit voltage loss. In this project, systematic studies on the self-assembled GeSi QDs readily controlled on miscut Si (001) substrates are carried out. By introducing deliberate surface microstructures, the precisely controlled growth of GeSi QDs, including density, distribution, size and shape of QDs, is realized on the miscut substrates. The physical properties of the controlled GeSi QDs are systematically investigated to clarify the band structure of QD, formation of the intermediate band and transition of carriers due to the coupling properties of QDs induced by the interaction between QDs. The relationship between the structural feature and photoelectric characteristics will be explored, thus drawing the optimized designing rule of strong coupling between QDs and obtaining silicon-based QD-IBSCs. The results obtained in this project will provide theoretical basis for designing silicon-based photovoltaic materials for IBSC.

半导体量子点是一种极具应用前景的高效中间能带光伏材料。但量子点中间带太阳能电池的转换效率仍远小于其理论值，其原因在于量子点体系存在密度低、空间有序性差和晶体质量不高的问题。这些问题弱化了量子点间的耦合作用，限制了中间能带的形成，不利于光子的吸收以及短路电流和开路电压的提高。本项目拟基于斜切Si（001）衬底表面可调原子台阶微结构对自组织GeSi量子点的动力学和热力学过程进行调控，以实现强耦合的高质量高密度有序GeSi量子点体系的可控制备；系统研究GeSi量子点间的耦合行为对量子点能带结构、中间能带形成和载流子输运机制等的影响；揭示GeSi量子点体系结构特征与光电特性的关系，形成强耦合GeSi量子点体系的优化设计原则，创制并优化基于GeSi量子点体系的硅基高效中间带太阳能电池。研究成果将为硅基高效量子点中间能带光伏材料的设计和制备提供理论依据。

半导体量子点是一种极具应用前景的高效中间能带光伏材料，但目前量子点体系的制备存在面密度低的问题，这严重的限制了中间能带的形成，不利于光子的吸收以及短路电流和开路电压的提高，进而导致量子点中间带太阳能电池的转换效率远小于其理论值。本项目着眼于高密度高质量GeSi量子点体系的可控制备及其耦合光电特性研究，取得的主要研究成果为：（1）利用分子束外延技术，系统研究了斜切衬底偏角、生长温度和沉积量等关键外延生长因素对GeSi量子点成核的影响。经过优化生长参数，实现了高密度高质量GeSi量子点的制备（面密度高达10的11方/cm2）；（2）采用荧光光致发光谱（主要包括功率变化光致发光谱和变温光致发光谱等）系统探究了GeSi量子点间的能级耦合行为、中间能带结构、态密度分布和激子行为等。实验发现，相对低密度量子点，高密度量子点具有更强的发光强度且其峰能量和峰宽不随光激发功率增加而变化，同时随温度的增加具有更加显著的红移和光衰减。实验结果证实了高密度量子点间中激子的去局域化行为和中间微带的形成。本项目研究成果揭示了高密度GeSi量子点间的结构特征与耦合光电特性之间的关系，为硅基高效量子点中间能带光伏材料的设计和制备提供理论依据。在课题资助下，以项目负责人为一作或者通讯作者发表SCI论文6篇，其中二区4篇，发表合作论文2篇，在国内学术会议做口头报告2次，培养研究生3名。