量子点中间带太阳电池通过对低于带隙能量光子的吸收，拓宽了太阳能光谱的利用范围，具有高的理论效率。然而，电池嵌入量子点后开路电压下降，使其整体效率远低于体材料电池。开路电压的降低，除了多层InAs量子点引入位错造成非辐射复合增强之外；快速的带内俄歇复合，破坏了导带和中间带准费米能级的分离是导致开路电压降低的另一个重要原因。本项目基于对量子点太阳电池光电流产生物理机理的分析，采用分子束外延生长方法，在GaAs电池结构中内嵌InAs/GaAsSb量子点，设计II类能带结构，使得电子和空穴波函数分离；通过对II类量子点载流子动力学以及量子点的存在对电池性能影响的研究，实现对载流子复合过程的控制，使得光偏置条件下电池导带、中间带、价带具有独立的准费米能级，解决电压下降问题；优化器件结构，最终实现中间带太阳电池的效率增加。项目的顺利开展，必为未来量子点中间带电池的广泛应用提供可靠的方案和理论支撑。

Intermediate band solar cells (IBSC) enable broadening the useful range of the solar spectra by absorbing the below band-gap energy photons, realizing high convention efficiency. InAs/GaAs quantum dots are used to make the intermediate band solar cells whereas the open circuit voltages reduce and the efficiencies are lower than the single gap solar cells. One reason is that the addition of multiple InAs QD layers builds up excessive strain and leads to defects, which act as non-radiative recombination centers and reduce the open circuit voltage. Another reason is that the fast electron relaxation from the conduction band (CB) to the intermediate band (IB), associated to the intraband Anger recombination, jeopardizes the quasi-Fermi level separation between CB and IB and open circuit voltage preservation in the IBSC. Base on the research on the photocurrent generation mechanism of the quantum dot solar cells, we use InAs/GaAsSb type II QDs instead of InAs/GaAs type I QDs to make the intermediate band solar cells. With the appropriate band structure engineering, electrons and holes are separated, and the intraband Anger recombination rate reduces. The material is grown by molecular beam epitaxy. We will research on the carrier dynamics of type II QDs and design its band structure to achieve the control of the carrier recombination process. The effect of InAs/GaAsSb QDs on the performance of the solar cells will be evaluated. If the quasi-Fermi level separations between CB and IB and also between IB and valence band (VB) are sustainable upon external excitation, the open circuit voltage is preserved, and ultimately its efficiency is enhanced. The accomplishment of this project will provide reliable theoretical support for the quantum dot intermediate band solar cells.