Differences of CIGS cell performance with Zn(O, S)/(Zn, Mg)O or CdS/i-ZnO buffers system explored by numerical simulations

Starting from the standard layer sequence of Mo/Cu(In, Ga)Se2/CdS/i-ZnO/ZnO:Al the cell n-side has been modified by replacing the CdS/i-ZnO with Zn(O, S) buffer in combination with (Zn, Mg)O as high-resistive layer, without changing the CIGS bulk. Measurements show a reduction of the cell performance compared to CdS/i-ZnO structure. In order to investigate the observed behavior, numerical simulations are used to examine the effect of the CIGS/Zn(O, S) interface properties on the cell performance. In particular, since the two sets of cells share the same CIGS, the effects on the solar cell's figures of merit of variations of the conduction band offset and defects properties at the buffer/absorber interface are analyzed

Improved growth of solution deposited buffer layers on Cu In,Ga Se2

CdS and Zn O,S grown by chemical bath deposition CBD are well established buffer materials for Cu In,Ga Se2 CIGS solar cells. As recently reported, a non contiguous coverage of CBD buffers on CIGS grains with 112 surfaces can be detected, which was explained in terms of low surface ener gies of the 112 facets, leading to deteriorated wetting of the chemical solutionon the CIGS surface. In the present contri bution, we report on the effect of air armealing of CIGS thin films prior to the CBD of CdS and Zn O,S layers. In cantrast to the growth on the as grown CIGS layers, these buffer layers grow densely on the annealed CIGS layer, even on grains with 112 surfaces. We explain the different growth behav ior by increased surface energies of CIGS grains due to the armealing step, i.e., due to oxidation of the CIGS surface. Reference solar cells were processed and completed by i ZnO ZnO Allayers for CdS and by Zn,Mg O ZnO Al for Zn O,S buffers. For solar cells with both, CdS and Zn O,S buffers, air annealed CIGS films with improved buffer cover age resulted in higher power conversion efficiencies, as com pared with the devices cantairring as grown CIGS layers