High efficiency p-i-n solar cells with layer deposited by hot-wire technique

More stable amorphous silicon (a-Si:H) material obtained with the hot-wire technique requires high substrate temperatures (T/sub sub/>300/spl deg/C) and low gas pressures (p/sub dep//spl ap/10/sup -2/ mbar). The second condition implies that heat transfer between the heater and the substrate is mainly dominated by thermal radiation; therefore, T/sub sub/ is strongly affected by the emissivity /spl epsi//sub surf/ of the growth surface. Here, it is shown experimentally that /spl epsi//sub surf/ depends on the thickness of the growing a-Si:H layer; a significant variation in /spl epsi//sub surf/ during the deposition of the first 3000 /spl Aring/ has been observed. With the help of a new heating concept, we integrated an intrinsic layer deposited at constant T/sub sub/=270/spl deg/C into a p-i-n solar cells with initial efficiency of 8.7%.