中间带掺杂中的Mott转变及载流子驰豫动力学的实验研究

Intermediate band based 3rd generation photovoltaic devices have drawn great attention in the past years. Because of its good harvesting of the solar energy in a wide spectrum,it makes the efficiency of single junction solar cell be possilbe to break the Shockley-Queisser limit which is 31%. But the present efficiency of the intermediate band solar cells are still very low, considering of its infant period. We are interested in the non-radiative recombination and carrier lifetime recovery in this system. Our research work will focus on some fundamental physics in the intermediate band materials and devices as follows. 1) We will try to achieve Mott transition in compound semiconductors by doping with deep centers, which will prepare materials suitable for interband solar cells. 2) We will study the influence of metal-insulator transistion on the non-radiative recombination, trying to find the mechanism for carrier lifetime recovery. This will help to solidify the theoretical basis for the working principle of intermediate band solar cells. 3) We will try to search afformatory experimental evidence for the splitting of quasi-Fermi levels between conduction band and intermediate band, which gives the missing link towards developing a working IB photovoltaic device. 4）After careful modelling and designning the device structure, we will fabricate a prototype intermediate band solar cell. We will try to demonstrate the effect and advantage of the intermediate band.

基于中间带材料的第三代光伏器件近年引起了学术界的巨大关注，由于它对太阳能光谱全波段的高效利用，使单结电池突破Shockley-Queisser理论效率极限(31％)成为了可能。但国际上中间带材料的实验工作刚刚起步，器件效率仍然偏低。本课题将从中间带材料中大家普遍关心的非辐射复合和载流子寿命恢复问题入手，围绕中间带材料和器件中一系列基础性物理问题，拟重点开展以下研究工作：1)探索在化合物半导体中通过深中心掺杂实现Mott转变的实验方案；2)研究中间带材料中金属-绝缘体转变对非辐射复合的影响，探寻载流子寿命恢复的机制，为中间带电池的发展提供更坚实的理论基石；3) 寻求导带和中间带之间准费米能级劈裂的确切实验证据，为中间带光伏器件的工作原理可行性补上关键的一环；4) 构建器件模型和优化器件结构，制作出基于中间带材料的光伏电池原型器件，力争成功演示中间带的效应和优势。

本课题从中间带材料中大家普遍关心的非辐射复合和载流子寿命恢复问题入手，围绕中间带材料和器件中一系列基础性物理问题，重点开展了以下研究工作：1) 中间带掺杂的理论设计，探索在化合物半导体中通过深中心掺杂实现长波太阳光的利用方案； 2) 研究中间带材料中的金属－绝缘体转变、非辐射复合抑制和载流子的寿命恢复问题； 3) 开展中间带材料中三个能带之间准费米能级劈裂的实验评价研究；4) 器件结构设计和中间带光伏电池。主要研究成果如下：1)从理论上筛选出了 CuGaSe2:Sn、CZTS:Ti和CuAlSe2:Ti三种极具前景的中间带太阳能电池材料；2)指出了中间带波函数离域化是抑制非辐射复合的关键，通过掺杂元素的选择（如筛选出的P、Sn、Ti），来控制导带和中间带的距离，可以减少导带电子向中间带的跃迁，从而提高载流子寿命，并在实验中得到了验证；3) 通过双光子吸收的量子效率光谱测量，我们成功证明 CuGaSe2:Sn和CZTS:Ti体系都表现出了部分三能级的特征，表明导带和中间带之间的费米能级实现了劈裂；4)制作出了CuAlSe2:Sn/CdS, CuGaSe2:Sn/CdS, CZTS:Ti/CdS等多种中间带太阳能电池原型器件，并得到了光电转换效率可达10.55%的器件。本项目的研究工作为第三代光伏器件的研究提供了重要理论支持和实验基础。