Witte, W.; Abou-Ras, D.; Hariskos, D.: Improved growth of solution-deposited buffer layers on Cu(In,Ga)Se2. Physica Status Solidi - Rapid Research Letters 10 (2016), p. 300-304
10.1002/pssr.201510454
Abstract:
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.