Effects of Mo back contact thickness on the properties of CIGS solar cells

Effects of Mo back contact thickness on the photovoltaic properties of CIGS solar cells were investigated. When the Mo was thin, an increase in series resistance and leakage current adversely affected the FF (fill factor) in solar cells fabricated using the Mo layers. On the other hand, when the thickness of the Mo layer was as thick as 0.8 μm, sodium out‐diffusion from the SLG decreased. The resulting reduced sodium concentration in CIGS films grown on top of the contact layers resulted in reduced open circuit voltage (VOC). As a consequence of the tradeoff between the decreased sodium diffusion for thicker Mo layers and reduced FF in thin Mo layers, the optimal Mo thickness was found to be 0.2 μm. Water vapor introduction during the deposition of the CIGS absorber layer was found to be effective in improving overall photovoltaic properties especially in solar cells with thin Mo back contacts. With water vapor introduction, cell efficiencies as high as 16.9% and 16.0% were obtained with Mo thicknesses of 0.2 μm and 0.07 μm, respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)