Evaluating the Potential of Polycrystalline Al0.25Ga0.75P and Al0.9Ga0.1As as Hole Contacts in Silicon Heterojunction Solar Cells

The parasitic absorption of visible light in amorphous silicon layers can result in a short-circuit current density (J_sc) loss of up to 2 mA/cm² for silicon heterojunction solar cells. To mitigate this issue, we explore the potential for polycrystalline Al_0.25Ga_0.75P and Al_0.9Ga_0.1As, both nonepitaxially deposited at 250 °C, to enable high J_sc while serving as alternative hole contacts to p-type amorphous silicon [a-Si:H(p)]. Using a suite of device characterization methods, we investigate how the passivation changes with the deposition of these III–V materials and their degree of hole selectivity. We identify that both Al_0.25Ga_0.75P and Al_0.9Ga_0.1As can still enable high implied open-circuit voltages >720 mV; however, they are not hole selective enough to enable high open-circuit voltage and fill factor. Ultimately, the best performing solar cells are limited to 9.6% and 10.8% efficiency with a nominal 5 nm of Al_0.25Ga_0.75P and a measured 13 nm of Al_0.9Ga_0.1As, respectively. However, both cells demonstrate higher J_sc than a reference cell with a-Si:H(p) that has a similar nominal thickness.