Localisation of front side passivating contacts for direct metallisation of high-efficiency c-Si solar cells

In this work, we present the development of passivating contacts based on thin interfacial oxide/doped polysilicon for two side contacted c-Si solar cells. In the first part, we discuss our layer optimization towards direct metallisation, using firing through of Ag-paste screen printed on a silicon nitride (SiNx:H). By optimising the poly-silicon thickness, we obtain solar cells with open circuit voltage (V-OC) up to 700 mV and fill factor (FF) up to 78%. However, such results were obtained by using layers with a thickness of 95 nm, strongly limiting the short circuit current density. To overcome this limitation, we present in the second part an approach for localization of the front side passivating contact by means of deposition through a shadow mask. Finally, in the third part, we demonstrate high-efficiency c-Si solar cells with promising efficiency above 21.7% with a V-OC of similar to 711 mV, a high FF of 79.7% and a potential for efficiency >22%.

Comparison of amorphous silicon absorber materials: Kinetics of light-induced degradation

Christophe Ballif, Adrian Billet, Mathieu Gérard Boccard, Matthieu Despeisse, Franz-Josef Haug, Yannick Samuel Riesen, Michael Elias Stückelberger

We investigate the influence of the deposition parameters for intrinsic amorphous silicon absorber layers on light-induced degradation (LID) of thin-film silicon solar cells. The focus is on absorber layers with different bandgaps: on one side, solar cells with a wide-bandgap absorber layer that provides open-circuit voltages up to 1.04V; on the other, cells with short-circuit current densities of 18.2mA/cm(2) with a 300-nm-thick narrow-bandgap absorber layer, and 20mA/cm(2) at reverse bias for a cell with a 1000-nm-thick absorber layer. Between these extremes, we varied the hydrogen-to-silane ratio and the deposition pressure during the absorber layer deposition. The light-induced degradation of these materialscovering the deposition regimes of low-pressure, protocrystalline, polymorphous, and high-pressure amorphous siliconincorporated in single-junction amorphous silicon solar cells is detailed here. For each pressure, we found an optimum hydrogen dilution with least LID close to the amorphous-to-microcrystalline transition. The relative LID is similar for all pressures at optimized hydrogen dilutions. Further, we present the influence of absorber layer thickness, p-layer thickness, and deposition rate on the kinetics of light-induced degradation to facilitate the choice of a material for its application in several types of multi-junction thin-film silicon solar cells. We show that the degradation kinetics depends, in semi-logarithmic scale, only weakly on time but more on deposition conditions. Copyright (c) 2014 John Wiley & Sons, Ltd.

Wiley-Blackwell2016

Phosphorous-Doped Silicon Carbide as Front-Side Full-Area Passivating Contact for Double-Side Contacted c-Si Solar Cells

Christophe Ballif, Matthieu Despeisse, Luca Gnocchi, Franz-Josef Haug, Andrea Ingenito, Philipp Friedrich Hermann Löper, Gizem Nogay, Josua Andreas Stückelberger, Philippe Wyss

We present an electron selective passivating contact based on a tunneling SiOx capped with a phosphorous doped siliconcarbideandpreparedwithahigh-temperaturethermalanneal. We investigate in detail the effects of the preparation conditions of theSiCx(n)(i.e.,gasﬂowprecursorandannealingtemperature)on the interface recombination rate, dopant in-diffusion, and optical properties using test structures and solar cells. On test structures, our investigation reveals that the samples annealed at temperatures of 800–850 °C exhibit an increased surface passivation toward higher gas ﬂow ratio (r = CH4/(SiH4 + CH4)). On textured and planar samples, we obtained best implied open-circuit voltages (i-VOC) of 737 and 746 mV, respectively, with corresponding dark saturation current densities (J0) of∼8 and∼4 fA/cm2. The SiCx(n)layerswithdifferentrvalueswereappliedonthetextured front side of p-type c-Si solar cells in combination with a borondoped SiCx(p) as rear hole selective passivating contact. Our cell results show a tradeoff between VOC and short-circuit current density (JSC) dictated by the C-content in the front-side SiCx(n). On p-type wafers, best VOC = 706 mV, FF = 80.2%, and JSC = 38.0 mA/cm2 with a ﬁnal conversion efﬁciency of 21.5% are demonstrated for 2 × 2 cm 2 screen-printed cells, with a simple and patterning-free process based on plasma depositions and one annealing step 800 °C < T < 850 °C for the formation of both passivating contacts.

2018

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

Christophe Ballif, Franz-Josef Haug, Andrea Ingenito, Frank Meyer, Sylvain Nicolay, Xavier Niquille

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.

2020