Amorphous silicon deposited by hot-wire CVD for application in dual junction solar cells

The hot-wire CVD technique is a promising method to deposit amorphous silicon at the same low temperatures as in PECVD. but at a much higher deposition rate maintaining a high material quality. We studied the role of the substrate temperature, the hydrogen dilution, and the silane gas flow rate on the film parameters. As the substrate temperature is lowered, the hydrogen concentration in the layers is increased. However, the electrical proper-ties of the HWCVD a-Si:H layers remain of device quality. Layers deposited at a temperature of 250 degreesC have been applied in efficient n-i-p solar cells on flexible stainless steel substrates, in which the doped. microcrystalline layers have been deposited by PECVD. No optical enhancement layers were used. The best cell has a fill factor of 0.72 and an open-circuit voltage of 0.89 V. An initial efficiency of 7.2% was measured. Although many cells show shunting problems, incorporation of the same material in amorphous silicon n-i-p/n-i-p tandem cells resulted in an initial efficiency of 8.5%. The results prove the feasibility of multi-junction cells with HWCVD absorber layers and the compatibility of these layers with plasma-deposited doped layers. (C) 2002 Elsevier Science B.V. All rights reserved.