Computational Design of Photovoltaic Materials with Self Organized Nano Structures

Chalcopyrite and II-VI semiconductors, such as Cu(In, Ga)Se$_{2}$, Cu$_{2}$ZnSn(S, Se)$_{4}$ and Cd(S, Te), are one of the most promising materials for low cost photovoltaic solar-cells. In this paper, based on first-principles calculations, we propose that self-organized nano-structures in these compounds will enhance the conversion efficiency. Our calculations are based on the KKR-CPA-LDA [1] with the self-interaction correction [2]. We also use VASP package [3] for calculating mixing energy and effective interactions of the systems by using the cluster expansion method [4]. For phase separating systems, we simulate nano-structure formation by using the Monte Carlo method. It is expected that the photo-generated electron-hole pairs are efficiently separated by the type-II interface and then effectively transferred along the quasi-one-dimensional structures. Moreover, we can expect multiplication of generated carriers due to the multi-exciton effects in nano-structures [5]. \\[4pt] [1] H. Akai, http://sham.phys.sci.osaka-u.ac.jp/kkr/\\[0pt] [2] A. Filippetti and N. A. Spaldin, PRB 67 (2003) 125109.\\[0pt] [3] G. Kresse and J. Hafner, PRB 47 (1993) 558.\\[0pt] [4] A. Zunger, NATO ASI B 319 (1994) 361.\\[0pt] [5] Y. Tani et al., APEX 3 (2010) 101201, 4 (2011) 021201, JJAP 51 (2012) 050202.