PROSPECTS OF WIDE-GAP CHALCOPYRITES FOR THIN-FILM PHOTOVOLTAIC MODULES

The development of a standard process for the fabrication of Cu(In,Ga) Se, thin film solar cells by coevaporation leads to highly efficient d evices with band-gaps in the range of 1-1.2 eV. The comparison of rece nt module efficiencies and the corresponding performance of small test cells demonstrates the high uniformity of the cell performance over l arge areas. In view of their higher open circuit voltage the use of ab sorbers with higher band-gaps is advantageous for the production of so lar modules. However, to date the efficiencies of cells employing chal copyrite absorbers with higher band-gaps lag behind. A consistent pict ure of the problems encountered in the case of wide-gap absorbers is d rawn on the basis of results from photoelectron spectroscopy in conjun ction with electrical measurements on the devices. This picture appoin ts the high efficiency of the cells with lower band gaps to the succes sful suppression of recombination at the heterointerface, resulting fr om a stabilized type inversion at the surface of the absorber. The for mation of such a type-inverted surface appears to be a prerequisite fo r the achievement of high efficiency with wide band-gap absorbers.