Ricerc@Sapienza

In crystalline silicon based heterojunction solar cells the surface passivation quality is fundamental to obtain high efficiency. Intrinsic a-Si:H, as obtained by PECVD process from silane dissociation, is a good candidate for surface passivation, but UV absorption of this material limits the current generation. Moreover, surface passivation quality can be compromised when fabrication steps, following the a-Si:H deposition, exceed the a-Si:H deposition temperature.

Hole-collecting and buffer layers more transparent than amorphous silicon layers are regarded as one of the possible improvements needed in amorphous/crystalline silicon heterojunctions to help reach the limit efficiency of silicon-based solar cells. Recent studies have demonstrated the suitability of sub-stoichiometric molybdenum oxide (MoOx) as hole-extracting layer in heterojunction solar cells based on n-type crystalline silicon. However, up to now MoOx has mainly been used in combination with amorphous silicon, so limiting its potential as a transparent emitter.

The fabrication of window layers more transparent than those based on amorphous silicon (a-Si:H) could be a key factor to enhance the efficiency of heterojunction (HJ) solar cells. In this work amorphous hydrogenated silicon oxide (a-SiOx:H) as a transparent passivating layer and substoichiometric tungsten oxide (WOx), with its wide band gap and high work function, are proposed to form efficient hole-selective contacts on silicon-based HJ solar cells. A comparison is made between WOx films grown by RF sputtering and by thermal evaporation.