Influence of Silicon Layers on the Growth of ITO and AZO in Silicon Heterojunction Solar Cells

• Published in: IEEE journal of photovoltaics 2020-03, Vol.10 (2), p.703-709
• Main Authors: Cruz, Alexandros, Schlatmann, Rutger, Stannowski, Bernd, Ruske, Florian, Eljarrat, Alberto, Michalowski, Pawel P., Morales-Vilches, Anna B., Neubert, Sebastian, Wang, Er-Chien, Koch, Christoph T., Szyszka, Bernd
• Format: Article
• Language: English
• Subjects: Aluminum; Aluminum doped zinc oxide (AZO); Amorphous silicon; Electron mobility; Glass; Heterojunctions; Hydrogen storage; Hydrogenation; Indium tin oxide; indium tin oxide (ITO); Indium tin oxides; Nanocrystals; Photovoltaic cells; Properties (attributes); Resistance; Secondary ion mass spectrometry; secondary ion mass spectrometry (SIMS); series resistance; Silicon; Silicon films; silicon heterojunction (SHJ); Solar cells; Substrates; Thin films; transmission electron microscopy (TEM); transparent conductive oxide (TCO); Zinc oxide
• ISSN: 2156-3381; 2156-3403
• DOI: 10.1109/JPHOTOV.2019.2957665

In this article, we report on the properties of indium tin oxide (ITO) deposited on thin-film silicon layers designed for the application as carrier selective contacts for silicon heterojunction (SHJ) solar cells. We find that ITO deposited on hydrogenated nanocrystalline silicon (nc-Si:H) layers presents a significant drop on electron mobility {\mu} _{{\rm{e}}} in comparison to layers deposited on hydrogenated amorphous silicon films (a-Si:H). The nc-Si:H layers are not only found to exhibit a larger crystallinity than a-Si:H, but are also characterized by a considerably increased surface rms roughness. As we can see from transmission electron microscopy (TEM), this promotes the growth of smaller and fractured features in the initial stages of ITO growth. Furthermore, secondary ion mass spectrometry profiles show different penetration depths of hydrogen from the thin film silicon layers into the ITO, which might both influence ITO and device passivation properties. Comparing ITO to aluminum doped zinc oxide (AZO), we find that AZO can actually exhibit superior properties on nc-Si:H layers. We assess the impact of the modified ITO R sh on the series resistance R_{s} of SHJ solar cells with >23% efficiency for optimized devices. This behavior should be considered when designing solar cells with amorphous or nanocrystalline layers as carrier selective contacts.