Optimization of the Solar Cell Structure for the Industrial Implementation in Very Large Area a-Si:H PV Modules

This paper reports on work performed in the FP7 European project HELATHIS. It presents the development of a TCO-glass combining a low iron-content substrate with a SnO2-layer with enhanced carrier mobility and therefore higher optical transmission, achieving in average 7.4% single junction module efficiency in TSolar standard production. First results of the further optimization of the fabrication process with this TCO glass indicate an increase of the single junction module efficiency in the future to nearly 8% in the stabilized state. Lightsoaking experiments of modules present very similar stabilized efficiency in the investigated i-layer thickness range between 140 to 260 nm, therefore, decreasing the i-layer thickness permits to increase the factory production capacity from about 55 up to about 75 MW/year. Investigation of the deposition of Al-doped ZnO layers by rf-sputtering from rotatable targets for the back reflector indicates improvement in the Isc and Voc. Implementation of such targets allows to expand the target life time and to reduce the maintenance time in comparison to standard planar targets. Ga-doped ZnO layers, when implemented in the back reflector, present similar cell performance compared with Al-doped ZnO.