Andrea Ingenito

Design and application of ion-implanted polySi passivating contacts for interdigitated back contact c-Si solar cells

Ion-implanted passivating contacts based on poly-crystalline silicon (polySi) are enabled by tunneling oxide, optimized, and used to fabricate interdigitated back contact (IBC) solar cells. Both n-type (phosphorous doped) and p-type (boron doped) passivating contacts are fabricated by ion-implantation of intrinsic polySi layers deposited via low-pressure chemical vapor deposition and subsequently annealed. The impact of doping profile on the passivation quality of the polySi doped contacts is studied for both polarities. It was found that an excellent surface passivation could be obtained by confining as much as possible the implanted-and-activated dopants within the polySi layers. The doping profile in the polySi was controlled by modifying the polySi thickness, the energy and dose of ion-implantation, and the temperature and time of annealing. An implied open-circuit voltage of 721 mV for n-type and 692 mV for p-type passivating contacts was achieved. Besides the high passivating quality, the developed ...

Optimized Metal-Free Back Reflectors for High-Efficiency Open Rear c-Si Solar Cells

The photovoltaic (PV) industry has recently become more oriented toward n-type c-Si solar cells. Among the different n-type solar cell architectures, bifacial cells are quickly emerging. The open-rear configuration of a bifacial device results in high transmittance (T) losses at long wavelengths (>1000 nm). This limitation is usually overcome at the module level either by using a bifacial encapsulation or by placing a reflective foil on the rear side. In this paper, we have investigated the application of a distributed Bragg reflector (DBR) and TiO2-based white paint (WP) as alternative metal-free back-reflector options applied to the textured open-rear of bifacial n-Pasha cells. Because of the high T losses at long wavelengths of the DBR applied on textured surface, its design and fabrication is studied in detail. The dielectric (DBR and WP) and optimized Ag back-reflectors, which are used as a reference, are applied to bifacial n-Pasha cells, and their performance is evaluated. In particular, we demonstrate T below 20% at 1200 nm by optimizing the DBR thickness for textured surfaces. In addition, the optimized DBR and WP show performance comparable with a state-of-the-art Ag back-reflector. The highest increase of the conversion efficiency is measured for the WP back-reflector: +0.34% absolute compared with n-Pasha measured with no-additional back-reflector.

Front/Rear Decoupled Texturing in Refractive and Diffractive Regimes for Ultra-Thin Silicon-Based Solar Cells

Front/rear decoupled texturing was studied experimentally in passivated c-Si wafer and theoretically in complete thin-film nc-Si:H solar cells. Measured and simulated absorptances in Si absorbers are close to or exceed the Yablonovitch limit.

Opto-electronic evaluation of thin double-textured crystalline silicon wafers

Light trapping accomplished by texturing of the wafer surface has produced a significant gain in solar cell performance of crystalline silicon solar cells. However, the continuous need of cost reduction requires the use of less raw material and cost-effective processes. To meet these requirements, more advanced light trapping schemes are needed. In this work we propose an approach for maximizing light absorption in thin silicon wafers. This light-trapping approach uses low cost and industrially scalable processes such as black silicon and random pyramids. The absorption measured on a series of thin silicon wafers was compared to single pass and Yablonovitch absorption limits. The electronic properties of wafers with the proposed light-trapping approach were also investigated.

Opto-electrical approaches for high efficiency and ultra-thin c-Si solar cells

The need for cost reduction requires using less raw material and cost-effective processes without sacrificing the conversion efficiency. For keeping high the generated photo-current, an advanced light trapping scheme for ultra-thin silicon wafers is here proposed, exhibiting absorptances up to 99% of 4n2 classical absorption limit for wafer thinner than 35 μm. Such excellent optical performance does not reflect optimal electronic properties due to high recombination rate of the nano-textured surface. Therefore, we propose a passivation method involving both wet etching and high quality passivation coating of the nano-textured surface. For wet etching time longer than 30 s recombination rate of the nano-textured surface reduced more than three time with respect to the un-etched one while keeping the averaged reflectance below 2% (between 300 and 1050 nm). Electrical simulations based on such findings indicate that for wafer thinner than 35 μm conversion efficiency higher than 25% can be achieved.

Photonic and plasmonic structures for applications in solar cells

The effect of decoupled front/back textures and the application of photonic and plasmonic nanostructures on the performance of thin silicon solar cells was studied. New light trapping concepts based on diffraction on periodic photonic nanostructures and scattering using plasmonic structures have potential to outperform the currently used randomly textured structures. The study demonstrates that supporting layers of solar cells, such as transparent conductive oxides, doped layers and back reflectors, are responsible for significant parasitic absorption losses that prevent achieving 4n2 enhancement of light absorption in solar cells with silicon absorbers.

Light Trapping Concepts for Enhanced Absorption in Thin Silicon Solar Cells

The effect of decoupled front/back textures and the application of photonic and plasmonic nanostructures on the performance of thin silicon solar cells was studied. The study shows that supporting layers of solar cells, such as transparent conductive oxides (TCO), doped layers and back reflectors (BR), are responsible for significant parasitic absorption losses that prevent achieving 4n2 enhancement of light absorption in solar cells with thin silicon absorbers.

Radial heterojunction c-Si nanowire solar cells with 11.8% conversion efficiency

Optical modelling and fabrication of hetero-junction c-Si nanowire solar cells is presented, including light propagation analysis and geometrical optimization. Performance of the fabricated device shows an unprecedented 11.8% conversion efficiency.