Theoretical evaluation of contact stack for high efficiency IBC-SHJ solar cells

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N‐type microcrystalline silicon carbide (μc‐SiC:H(n)) is a wide bandgap material that is very promising for the use on the front side of crystalline silicon (c‐Si) solar cells. It offers a high optical transparency and a suitable refractive index that reduces parasitic absorption and reflection losses, respectively. In this work, we investigate the potential of hot wire chemical vapor deposition (HWCVD)–grown μc‐SiC:H(n) for c‐Si solar cells with interdigitated back contacts (IBC). We demonstrate outstanding passivation quality of μc‐SiC:H(n) on tunnel oxide (SiO2)–passivated c‐Si with an implied open‐circuit voltage of 742 mV and a saturation current density of 3.6 fA/cm2. This excellent passivation quality is achieved directly after the HWCVD deposition of μc‐SiC:H(n) at 250°C heater temperature without any further treatments like recrystallization or hydrogenation. Additionally, we developed magnesium fluoride (MgF2)/silicon nitride (SiNx:H)/silicon carbide antireflection coatings that reduce optical losses on the front side to only 0.47 mA/cm2 with MgF2/SiNx:H/μc‐SiC:H(n) and 0.62 mA/cm2 with MgF2/μc‐SiC:H(n). Finally, calculations with Sentaurus TCAD simulation using MgF2/μc‐SiC:H(n)/SiO2/c‐Si as front side layer stack in an IBC solar cell reveal a short‐circuit current density of 42.2 mA/cm2, an open‐circuit voltage of 738 mV, a fill factor of 85.2% and a maximum power conversion efficiency of 26.6%.

Section: Resultssupporting

confidence: 86%

Section: Methodssupporting

confidence: 86%

Section: Methodsmentioning

confidence: 99%

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Transparent silicon carbide/tunnel SiO₂ passivation for c‐Si solar cell front side: Enabling J_sc > 42 mA/cm² and iV_oc of 742 mV

Pomaska

Köhler

Procel

et al. 2020

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“…Accurate opto‐electrical simulations of poly‐poly solar cells are performed using a modelling framework based on TCAD Sentaurus,combining thin film optics and opto‐electrical properties, such as free carrier absorption. The simulated structure is reported in Figure C using experimentally extracted wavelength‐dependent refractive index of poly‐Si .…”

Section: Methodsmentioning

confidence: 99%

Implantation‐based passivating contacts for crystalline silicon front/rear contacted solar cells

Limodio

Yang

Groot

et al. 2020

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In this work, we develop SiOx/poly‐Si carrier‐selective contacts grown by low‐pressure chemical vapor deposition and boron or phosphorus doped by ion implantation. We investigate their passivation properties on symmetric structures while varying the thickness of poly‐Si in a wide range (20‐250 nm). Dose and energy of implantation as well as temperature and time of annealing were optimized, achieving implied open‐circuit voltage well above 700 mV for electron‐selective contacts regardless the poly‐Si layer thickness. In case of hole‐selective contacts, the passivation quality decreases by thinning the poly‐Si layer. For both poly‐Si doping types, forming gas annealing helps to augment the passivation quality. The optimized doped poly‐Si layers are then implemented in c‐Si solar cells featuring SiO2/poly‐Si contacts with different polarities on both front and rear sides in a lean manufacturing process free from transparent conductive oxide (TCO). At cell level, open‐circuit voltage degrades when thinner p‐type poly‐Si layer is employed, while a consistent gain in short circuit current is measured when front poly‐Si thickness is thinned down from 250 to 35 nm (up to +4 mA/cm2). We circumvent this limitation by decoupling front and rear layer thickness obtaining, on one hand, reasonably high current (JSC‐EQE = 38.2 mA/cm2) and, on the other hand, relatively high VOC of approximately 690 mV. The best TCO‐free device using Ti‐seeded Cu‐plated front contact exhibits a fill factor of 75.2% and conversion efficiency of 19.6%.

“…Typically, SHJ contact stack structures consist of intrinsic and doped a‐Si:H thin layers (less than 15 nm) grown by plasma‐enhanced chemical vapor deposition (PECVD). Theses Si cells with thin‐film layers must also feature certain properties to build efficient contacts in terms of carrier selectivity and carrier selective transport for obtaining a high fill factor ( FF ) . Such layer properties point to minimal activation energy ( E a ) for both contacts whereas wider bandgap ( E g ) is more favorable for the collection of holes (p‐contact).…”

Section: Introductionmentioning

confidence: 99%

Doped hydrogenated nanocrystalline silicon oxide layers for high‐efficiency c‐Si heterojunction solar cells

Zhao

Mazzarella

Procel

et al. 2020

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Hydrogenated nanocrystalline silicon oxide (nc‐SiOx:H) layers exhibit promising optoelectrical properties for carrier‐selective‐contacts in silicon heterojunction (SHJ) solar cells. However, achieving high conductivity while preserving crystalline silicon (c‐Si) passivation quality is technologically challenging for growing thin layers (less than 20 nm) on the intrinsic hydrogenated amorphous silicon ((i)a‐Si:H) layer. Here, we present an evaluation of different strategies to improve optoelectrical parameters of SHJ contact stacks founded on highly transparent nc‐SiOx:H layers. Using plasma‐enhanced chemical vapor deposition, we firstly investigate the evolution of optoelectrical parameters by varying the main deposition conditions to achieve layers with refractive index below 2.2 and dark conductivity above 1.00 S/cm. Afterwards, we assess the electrical properties with the application of different surface treatments before and after doped layer deposition. Noticeably, we drastically improve the dark conductivity from 0.79 to 2.03 S/cm and 0.02 to 0.07 S/cm for n‐ and p‐contact, respectively. We observe that interface treatments after (i)a‐Si:H deposition not only induce prompt nucleation of nanocrystals but also improve c‐Si passivation quality. Accordingly, we demonstrate fill factor improvement of 13.5%abs from 65.6% to 79.1% in front/back‐contacted solar cells. We achieve conversion efficiency of 21.8% and 22.0% for front and rear junction configurations, respectively. The optical effectiveness of contact stacks based on nc‐SiOx:H is demonstrated by averagely 1.5 mA/cm2 higher short‐circuit current density thus nearly 1%abs higher cell efficiency as compared with the (n)a‐Si:H.