Effects of a post deposition anneal on a tunneling Al2O3 interlayer for thermally stable MoOx hole selective contacts

An a-Si:H(i)/MoOx contact gives excellent surface passivation but often leads to carrier-selectivity issues upon thermal treatments, and is limited by parasitic absorption originating from the a-Si:H(i) interlayer. Alternatively, a superior contact transparency, combined with a better hole selectivity can be obtained by replacing the a-Si:H(i) by an atomic layer deposited (ALD) Al2O3 interlayer. In this work, we show that good surface passivation and thermal stability at temperature up to 210 °C, can be achieved by using this scheme. As a result, a starting efficiency of 18.2% was achieved on a 6" c-Si solar cell, with industrial processing based on screen-printing. Additionally, we showed that a post-deposition anneal (PDA) treatment on the Al2O3 interlayer – prior to MoOx deposition - can further improve the surface passivation of the contact. However, such treatment also makes the contact more sensitive to ITO sputtering damage and impedes the hole transport through the Al2O3 interlayer.