Transparent conductive electrodes for flexible solar cells

Within the next decades flexible solar cells will gain considerable importance for both mobile devices and building integrated systems. The effective deposition of transparent conductive electrodes is of major importance for the intended low device price of the cells. The paper will review the presently available electrode concepts. The application of both single layer and multi layer transparent electrodes to various types of solar cells will be discussed. The paper will present own results for the deposition on plastic substrates at low temperatures. In this field ITO is still pursuing a dominant role. It could be shown that the properties of the deposited layers depend on the lateral position of the substrate with respect to the ITO target. Different settings of both the sputtering mode and the gas composition in the sputtering atmosphere were investigated. In all cases the energetic particle bombardment during sputtering was influenced and consequently the lateral distribution of optical and electrical properties of the ITO layer was changed. These results were applied to a roll-to-roll coating machine. ITO was sputtered in a continuous process from a double ceramic target. Specific resistance values below 5xlO(exp-4) Ohm/sq could be achieved.