Carrier selective contacts are essential for solar cells. So far, nanowire solar cells as traditional silicon solar cells mainly rely on impurity doping to create two carrier selective regions. However, the precise doping control for nanowires in the sub-µm range is very challenging and strongly affected by the exact geometry and growth conditions. Alternatives are high and low work function interfacial layers, such as MoOx and LiF, that have already been employed for wafer-based silicon solar cells. They create carrier selectivity by inverting the underlying semiconductor and forming a heterojunction.<br/>In general, a high degree of surface passivation is crucial for contact selectivity, too. Unpassivated interface defects can lead to Fermi-level pinning, which can create charge carrier extraction barriers and even counteract the influence of interfacial layers or dopants.<br/>In this work we study the detrimental impact of Fermi-level pinning, due to the native oxide of InP, on the carrier selectivity for p-type InP nanowires. We conduct I-V measurements of single nanowire devices before and after HF treatment. In the next step we apply the contact layer MoOx which mitigates negative effects due to inhomogeneous dopant incorporation. As a result, the open-circuit voltage increases by up to 335 mV, from 500 mV to 835 mV. Finally, we propose the use of a molecular passivation layer, sandwiched between the unoxidized InP surface and the high work function layer MoOx for both decreased surface recombination and increased carrier selectivity.

Carrier selective contacts for nanowire solar cells

253rd National Meeting (2017)

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