Low-temperature aluminium doped a-Si as hole selective contacts on p-type silicon solar cells

Although doped a-Si:H (hydrogenated amorphous silicon) as carrier transport layers provides superior carrier selectivity and moderate resistive losses, the parasitic absorption of free carriers and complex doping techniques are still limiting factors. In this report, we present a novel application of aluminum (Al) doped a-Si:H (through an annealing process below 200 °C) as hole selective contacts (HSCs) on p-type silicon (p-Si) solar cells. This gives a simplified doping method as an alternative for the conventional in situ a-Si:H doping technique. Band alignment profiles of p-Si/a-Si:H/Al stack are presented, suggesting the feasibility of hole-selectivity, and explaining the cause of a transformation from a Schottky behaving contact to an ohmic contact. As proof of this inference, a rectifying Al contact on p-Si (with an intrinsic a-Si:H interlayer) is shown to be ohmic after annealing at 190 °C for 5 minutes. An actual device featuring a full area Al-doped a-Si:H contact layer has been fabricated, achieving an efficiency of 16.3%.