Optimization of front SiNx/ITO stacks for high-efficiency two-side contacted c-Si solar cells with co-annealed front and rear passivating contacts

• Published in: Solar energy materials and solar cells 2021-01, Vol.219, p.110815, Article 110815
• Main Authors: Meyer, Frank, Savoy, Arnaud, Diaz Leon, Juan J., Persoz, Marc, Niquille, Xavier, Allebé, Christophe, Nicolay, Sylvain, Haug, Franz-Josef, Ingenito, Andrea, Ballif, Christophe
• Format: Article
• Language: English
• Subjects: Annealing; Antireflection coatings; Carrier density; Circuits; Crystal defects; Crystal structure; Crystallinity; Heat treatment; Hydrogen; Hydrogenation; Indium tin oxides; Indium-tin-oxide (ITO); Low temperature; Open circuit voltage; Optimization; Passivating contacts; Photovoltaic cells; Short circuit currents; Short-circuit current; Silicon; Silicon nitride; Silicon oxide; Silicon oxides; Silicon solar cells; Solar cells; Spectral sensitivity; Sputtering; Tin; Voltage; Wavelengths
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2020.110815

In this contribution, we present an electron selective passivating contact metallised with a low temperature process to target front side applications in crystalline silicon (c-Si) solar cells. In addition to an interfacial silicon oxide (SiOx) and an in-situ phosphorous doped micro-crystalline silicon (μc-Si(n)) layer, it comprises an ultra-thin indium tin oxide (ITO) layer of 15 nm for lateral conductivity and a hydrogen rich silicon nitride (SiNx:H) layer which serves as hydrogen (H) reservoir and as anti-reflection coating. We use one single thermal treatment for 30 min at 350 °C to sinter the screen-printed paste, to recover sputtering damage induced during ITO deposition, and to diffuse hydrogen from the SiNx:H layer towards the c-Si/SiOx interface where it passivates interfacial defects. Applied to symmetrically processed textured samples, we find implied open-circuit voltage (iVOC) > 728 mV for optimal ITO thickness of 15 nm and annealing temperatures of 350 °C. The developed stack was applied on the front textured side of co-annealed (800 °C) p-type c-Si solar cells in combination with a tunnel oxide hole selective passivating contact on the rear side. We demonstrate solar cells with fill factor (FF) up to 81.9% and an open-circuit voltage (VOC) up to 719 mV. With a short-circuit current density (JSC) of 38.6 mA/cm2, we obtain a final cell efficiency to 22.8%. We find that the annealing of the SiNx:H/ITO stack strongly increases the ITO free carrier density penalizing the solar cell spectral response at high wavelengths. •Full-area highly transparent passivating front contact for p-type solar cells.•Ultra-thin ITO layer of 15 nm yields excellent current extraction with FF of almost 82%.•One single annealing step for hydrogenation and curing of sputtering damage.•SiNx:H no longer sacrificial layer but part of the ARC.