XIS: A Low-current, High-voltage Back-junction Back-contact Device

AbstractIn this paper we present experimental results of a low-current, high-voltage back-junction back-contact device. The concept is demonstrated by the successful transformation of finished IBC cells into XIS (Crystalline Silicon Interconnected Strips) devices, leading to 8.5V for a series connection of 14 strip cells. Different grooving methods for cell separation were evaluated regarding the effect on the quality of the groove surface. The effect of the groove passivation, which is regarded as a critical parameter to obtain high-efficiency XIS devices, was simulated to gain a better understanding of the processing requirements

Seeded-Growth Approach to Selective Metallization of Microcontact-Printed Patterns

We report on a versatile nanocolloidal route to obtain large-scale conducting metal microstructures on a silicon oxide substrate. By using microcontact printing of an aminosilane, we create functionalized regions on the silicon oxide surface onto which gold nanoparticles selectively adhere. By using an established electroless, seeded-growth process, the individual, isolated gold nanocrystals are enlarged past the percolation threshold to form conducting metal structures. Quantitative characterization of metal coverage, thickness, and roughness has been performed with scanning electron microscopy and spectroscopic ellipsometry

Ellipsometric study of percolation in electroless deposited silver films\ud

Using spectroscopic ellipsometry in the visible and near-infrared spectral range we investigate the optical properties of a growing silver film starting from predeposited gold nanoparticles. The effective pseudodielectric functions, obtained by direct inversion of the ellipsometry spectra, reveal a surface plasmon resonance for the nanoparticulate films. Upon prolonged electroless silver deposition, the resonance shifts to lower energies. The redshift is due the longer electron mean free path in larger silver structures and is analyzed by describing the optical response of the developing silver film in terms of a Lorentz line shape. The position of the oscillator, i.e., its resonance energy, is discussed in relation to the transition from isolated nanoparticles to an interconnected, eventually continuous metal film. This transition is also observed in the optical conductivity which exhibits an abrupt, stepwise increase at the same energy where the aforementioned resonance energy becomes zero. For longer deposition times, the optical spectra can be described in terms of a Drude-like free-electron metal. The development of the Drude–Lorentz parameters, i.e., the relaxation time and electron density, are compared to values for bulk silver; the latter were obtained from an optical measurement on a thick bulk silver sample. The saturation values for the relaxation time and thus the conductivity amount to approximately 40% of the bulk value, in agreement with direct current conductivity measurements on these films.\u

On the hydrogenation of Poly-Si passivating contacts by Al2O3 and SiNx thin films

Doped polycrystalline silicon (poly-Si), when coupled with a thin SiO2 interlayer, is of large interest for crystalline silicon (c-Si) solar cells due to its outstanding passivating contact properties. To reach high levels of surface passivation, it is pivotal to hydrogenate the poly-Si and the underlying c-Si/SiO2 interface. This can be done by capping the poly-Si with a hydrogen-containing dielectric layer such as Al2O3 or SiNx, followed by a thermal anneal. On the basis of recent research, this work addresses several aspects of such hydrogenation by dielectric materials, including the effect of the annealing ambient, the thermal stability and reversibility of hydrogenation, the poly-Si doping level and c-Si surface texture. Additionally, the implementation of hydrogenation of poly-Si by dielectric materials in solar cells is discussed

High resolution sheet resistance mapping to unveil edge effects in industrial IBC Solar Cells

We present Terahertz (THz) transmission measurements with a spatial resolution of down to 10 μm as a new inspection technique for high-resolution sheet resistance (Rsh) measurements, that are well suited to quantify the local Rsh (n-type and p-type regions) of interdigitated back-contact (IBC) structures and to support further optimization of our IBC cells.\u3cbr/\u3e\u3cbr/\u3eUsing this technique, we investigated the homogeneity of the emitter of our IBC cells. We have greatly improved the Rsh homogeneity of the boron diffusion. Moreover, we compared THz mapping with standard four point probe (4pp) technique. While the 4pp measurement showed a homogeneous mapping, the THz could unveil elevated Rsh near the very edge of the wafer. Higher Rsh of the surface doping can result in higher J0 at the metal contact regions (J0,contact). A local Voc mapping technique was used and it was found that the local Voc at the wafer edge was lowered by 17 mV compared to the centre in the most extreme case. We estimate that an improved edge doping could result in a performance gain of at least 0.2% absolute, excluding FF and Jsc benefits.\u3cbr/\u3e\u3cbr/\u3eIn summary we show that THz mapping is a powerful method in determining inhomogeneities and can aid in the development of diffused-junction IBC solar cells.\u3cbr/\u3

Mercury:industrial IBC cell with front floating emitter for 20.9% and higher efficiency

\u3cp\u3eIn this paper break-through results on our 6? industrial Mercury cells are presented. We gained more than 1% absolute in efficiency by optimizing the processes and design of the cells, resulting in 20.9% cell efficiency. We used standard industrial equipment and the number of process steps similar to our commercial n-Pasha technology. The screen-printed IBC cells can be interconnected by our proven industrial foil-based interconnection scheme. Together with this result, we present a method to characterize and quantify the pn-junction recombination contribution to Voc and pseudo-FF losses in the cell. Finally, our roadmap to 23% Mercury cells is presented.\u3c/p\u3