新型多元太阳能电池材料中基本物理问题的计算研究

Significant breakthrough has been made in the research about new solar cells based on the Cu2ZnSn(S,Se)4 and CH3NH3Pb(I,Cl)3 multinary semiconductors, showing that these multinary semiconductors may become very promising absorber-layer materials in next-generation solar cells. Compared to simple elemental and binary semiconductors, multinary compound semiconductors have much more flexible material properties, which are also more complicated and sometimes even abnormal. Fundamental physical problems arise in how these complicated (even abnormal) properties influence the photovotalic performance. To improve the solar cell performance, we will consider the increased chemical and structural freedom of multinary semiconductors, and develop more accurate methods for calculating the properties of multinary compounds as well as the generation, separation and recombination rates and transport properties of the electron-hole carriers based on the first-principles methods. Using the new methods, we will study the intrinsic defects, surfaces and interfaces in the multinary semiconductors and their alloys, as well as their influence on the generation, separation and recombination of the electron-hole carriers. Meanwhile, the phase stability of multinary compounds relative to their competitive compounds and the structural transformation between different phases will be studied too. Based on these results, we will reveal the fundamental and general mechanisms that determine the photovoltaic performance of multinary semiconductors, and find out new methods for optimizing the solar cell performance and stability.

以Cu2ZnSn(S,Se)4、CH3NH3Pb(I,Cl)3为代表的新型多元半导体太阳能电池的研究在近几年取得了突破性的进展，是下一代太阳能电池的希望。与传统一元二元半导体相比，多元半导体基本物理、化学性质更加丰富，但也更加复杂，甚至可以表现出很多与传统简单半导体所不一样的反常特征，同时出现了一系列新的物理问题，影响着器件的性能。为了进一步改善电池性能，本项目拟从多元半导体成分和结构自由度增多这一基本特征出发，在第一性原理的框架内，发展更加精确计算多元半导体性质，特别是其中载流子产生、分离、复合几率和输运性质的方法，研究多元半导体及其合金中的复杂缺陷、表面、界面及其对载流子性质的影响，并研究多元体系相稳定性的规律，探索提高稳定性和光电转换效率的新途径。

该项目对多元太阳能电池材料中基本物理问题开展了系统研究。主要研究了电池中界面结构和电子结构，特别是能带带阶，吸收材料中的非本征缺陷性质，例如晶界产生的缺陷态及其消除方法，缺陷态引起的无辐射跃迁几率计算，以及一些新型太阳能吸收的性质等。在如下几个方面研究取得了重要进展：.1.提出了三步法和中间相方法，从而完全解决了异质半导体界面带阶(band-offset)的计算问题。.2.计算发现不同半导体体系晶界缺陷态特征，提出了晶界缺陷态的自饱和规则，为理解和消除太阳能电池中晶界缺陷态提供了基础。.3.提出了通过优化吸收材料与过渡层界面、吸收材料与背电极界面从而提高器件效率的方案，其中优化吸收材料与过渡层界面的方案得到实验证实和采纳。.4.实现了基于第一原理的计算非辐射复合的快速计算方法和软件，证实了四元半导体太阳能吸收材料和钙钛矿太阳能吸收材料中的最主要的非辐射缺陷。.5.计算发现，有机无机钙钛矿材料（MAPbI3）是热力学本证不稳定的，被后续的实验和理论证实。.项目组共发表SCI收录论文31篇、材料模拟计算handbook一章、一个软件著作权。为多元太阳能电池等发展起到了推动作用。