Molybdenum and tungsten oxide: High work function wide band gap contact materials for hole selective contacts of silicon solar cells

The high work function metal oxides, tungsten oxide (WO. <inf>x</inf> ) and molybdenum oxide (MoO. <inf>x</inf>), were investigated regarding their ability to form a hole-selective contact for a crystalline silicon absorber. We show that in principle both materials have the potential to (i) either replace the p-type amorphous silicon thin films typically used as the high work function contact material in silicon based heterojunction solar cells or (ii) to assist the hole extraction if used as an additional contact layer placed between the p-type amorphous silicon and the TCO electrode. For an integral evaluation of the actual loss mechanisms limiting the contact characteristics both the ability of the contact scheme to passivate the absorber and to selectively extract the excess holes from the absorber are analyzed.