Improving the thermal stability of polycrystalline silicon passivated contacts using aluminium doped zinc oxide interlayers

We study the development of aluminium doped zinc oxide (AZO) protective interlayers for thin polycrystalline silicon (poly-Si) passivated contacts. The study is motivated by a need to reduce parasitic absorption in poly-Si passivated contacts by thinning the poly-Si layers, without making them fragile to metal overlayers. Several combinations of protective interlayers are studied with n-type poly-Si contacts including AZO-only films as well as AZO capped with various AlOx layers. All combinations improve the thermal stability of the n-type poly-Si contacts at the expense of increased contact resistivity. The best protective films are the AZO-only films and the AZO capped with a thin thermally evaporated Al layer (which partially oxidises under air exposure). These maintain original levels of surface passivation (iVoc ~720 mV) after metallisation and annealing up to 500 oC and have contact resistivity values in the ρc of 10-45 mΩ-cm2 range, suitable for large area contacts. As such, we demonstrate one pathway for utilising thin poly-Si passivated contacts in high efficiency silicon solar cells and improving the reliability of silicon bottom solar cells in perovskite/silicon tandem solar cells.