Silicon-based ultrathin layers for hole-selective contacts in silicon solar cells

Abstract

This thesis presents a collection of work investigating the optoelectronic properties of atomic layer deposited silicon nitride nanolayers as a hole-selective tunnelling layer in passivating contacts for silicon solar cells. We also look at forming p-type polycrystalline silicon as charge modulation layers for such contacts via hot wire chemical vapour deposition. Carrier-selective passivating contacts are currently the state-of-the-art in terms of exceeding current power conversion efficiency barriers in high performance solar cell architectures. To date, less success has been achieved with hole-selective contacts than with electron-selective contacts. In this thesis, we first study the growth quality of polycrystalline silicon films using a hot wire process. We optimise the morphological characteristics towards creating more uniform films that require minimal post-deposition heat-treatment. Following this, we investigate using ultrathin silicon nitride as a tunnelling layer that can both reduce parasitic losses associated with charge carrier recombination and promote hole transport. For the first time in literature, we present an experimental report on the band alignments at the SiN-Si heterojunction interface, showing favourability towards hole transport. We then look at contact formation using various metal electrodes on our heterojunction, studying the specific contact resistivity. Finally, we show the prospects of a poly-Si/SiN/Si heterocontact via Sentaurus TCAD, with direct comparisons of carrier tunnelling probability and tunnelling current in a tunnelling oxide passivating contact counterpart. For SiN and SiO2 films of equivalent thickness, hole current densities are predicted to be at least ten times higher in SiN. This work takes important steps towards forming high-performance carrier-selective contacts that can be utilized in multiples avenues of photovoltaics research.

More information

Identifiers

ORCID for Stuart Boden: orcid.org/0000-0002-4232-1828

Catalogue record

Export record