Very high deposition rate μc-Si:H absorber layer deposition using a plasma excitation frequency of 140 MHz in combination with high process pressures

摘要

The reduction of costs of silicon based thin-film solar cells is of major importance in terms of the competitiveness of the technology. One major costfactor of silicon thin-film solar cells is the absorber layer deposition of the micr°Crystalline silicon (μc-Si:H) bottom cell of tandem devices. In this workresults of the ultra fast μc-Si:H absorber layer deposition are described. The content of this study covers the research activities of work package 4 of theEuropean FAST TRACK project. To achieve the high deposition rate targets a plasma regime which combines high pressures and high power levels atan electrode distance of 10 mm is used. Furthermore, in this study a μc-Si:H p-i-n solar cell structure entirely deposited at 140 MHz was developed. Theuse of a plasma excitation frequency of 140 MHz for the entire μc-Si:H solar cell structure is novel in the field of silicon thin film photovoltaics.At the beginning a μc-Si:H p-i-n reference pr°Cess at moderate i-layer deposition rates (0.8 nm/s) was developed. After several optimization steps anefficiency of 8.3 % could be achieved at an i-layer deposition rate of 0.8 nm/s. In the next step the deposition rate of the absorber was increased up to5 nm/s. The typical shift of the phase transition to higher silane concentration ratios could be observed when increasing the power density. Promising ilayermaterial with rates up to about 2.1 nm/s was incorporated into complete μc-Si:H p-i-n solar cells. A slight decrease of the solar cell parameters η,FF, U°C and Jsc was observed with increasing absorber deposition rate. Finally, an initial efficiency of 6.9 % could be achieved at an absorber layerdeposition rate of 2.1 nm/s.