Optical management in high-efficiency thin-film silicon micromorph solar cells with a silicon oxide based intermediate reflector



In the effort to increase the stable efficiency of thin film silicon micromorph solar cells, a silicon oxide based intermediate reflector (SOIR) layer is deposited in situ between the component cells of the tandem device. The effectiveness of the SOIR layer in increasing the photo-carrier generation in the a-Si:H top absorber is compared for p–i–n devices deposited on different rough, highly transparent, front ZnO layers. High haze and low doping level for the front ZnO strongly enhance the current density (Jsc) in the μc-Si:H bottom cell whereas Jsc in the top cell is influenced by the angular distribution of the transmitted light and by the reflectivity of the SOIR related to different surface roughness. A total Jsc of 26.8 mA/cm2 and an initial conversion efficiency of 12.6% are achieved for 1.2 cm2 cells with top and bottom cell thicknesses of 300 nm and 3 μm, and without any anti-reflective coating on the glass. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)