Semiconductors for thin film solar cell applications

The thin film CuIn_xGa_1-xS₂-Solar Cell (CIGS) uses layer thicknesses that are by far smaller (factor~100) than Si-solar cells. This leads to a much smaller material absorptivity and efficiency. Solar cells with high conversion efficiency also use dwindling resources like Te, Se, Ga or In. For these elements a cheap, but still efficient replacement has to be found. Candidates are the wide band gap semiconductors with C1_b structure. Again these ternary compounds can be made of cheap elements and easily be optimized by substitution. The aim of our group is to find new materials that replace CdS and In in CIGS. LiCuS is a newly designed compound, which has just the same electronic properties as CdS. The compound can be sputtered and independent from the exact stoichiometry of the sputter targets, the thin films are always as yellow as CdS, a basic starting criterion of final utility. In this field we cooperate closely with industrial enterprises (IBM and Schott) and with the Helmholtz Zentrum Berlin für Materialien und Energie and the TU Darmstadt. Our focus in the future will be more general. These wide band semiconductors can be used as solar cells and for other optoelectronic applications. The systematic screening of the ternary semiconductors for thin film solar cells and for light emission diodes is one of my visions for the near future.

On the theoretical side, we develop together with T. Schilling (Mainz) a computer program for the calculation of the electronic and magnetic properties of disordered materials and interfaces. The program will be based on the combination of density functional and Monte Carlo methods. Starting points are existing computer programs for electronic structure calculations. The goal is to calculate the electronic structure of the optimized crystalline structure in presence of defects in solids as well as at interfaces between different materials. The program will be applied to the search for new, improved materials for solar cells with increased efficiency.

 

Key papers and collaborators:
I-II-V half-Heusler compounds for optoelectronics: Ab initi calculations, David Kieven, Reiner Klenk, Shahab Naghavi, Reiner Klenk, Thomas Gruhn, Claudia Felser, Phys. Rev. B accepted

 

International Collaborations:

A. Zunger NREL, Colorado

 

Industrial Collaborations:
Schott, Mainz, IBM MAINZ, Helmholtz Zentrum Berlin für Materialien und Energie