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AbstractExamination of results from the pilot production of buried‐contact solar cells (BCSC) allows several new insights into the effects of the substrate resistivity, the differences between upright and inverted pyramid texturing, the reflection after encapsulation and the doping level at which the emitter begins to dominate the overall recombination. A lower substrate resistivity in conjunction with thicker wafers reduces the effects of a high back surface recombination velocity and allows both higher voltages and efficiencies. In BCSCs with low substrate resistivities, the voltage is not limited by the back but by the emitter diffusion and the dislocation formation at the surface. Contrary to previous reports, best results have been realized with upright pyramids rather than inverted pyramids. In addition, the relative performance of the upright pyramids improves after encapsulation owing to the less than optimal unencapsulated reflection of these surfaces in the regions of the pyramid peaks where oxide layers are too thin to gain benefits as an antireflection layer. Recent results also indicate that the contributions to the dark saturation current from both the heavily phosphorus‐diffused region beneath the metal contact and the more lightly diffused top surface emitter are less than indicated previously. Finally, comparison between experimentally obtained voltages and those predicted through modelling with PC‐1D provides an estimate of the bulk material lifetimes in the pilot line cells.

The lifetime of high energy phonons in a QD superlattice is computed for plausible model materials from Time Dependent Perturbation Theory (TDPT). Klemens decay can be inhibited for a range of high energy phonons if a significant phonon bandgap exists. Ridley-type decays can compete with Klemens for speed due to the large density of states available for decay products on some decay paths and are typically a few picoseconds. In diamond superlattices where QDs occupy the majority of the unit cell, computed lifetimes can be as long as hundreds of picoseconds for certain symmetry directions.

Abstract This paper demonstrates that a double-layer antireflection (DLAR) coating can be fabricated using a single material, titanium dioxide (TiO2). The optical properties of the top and bottom TiO2 layers were controlled by varying the deposition and sintering conditions, resulting in a range of refractive indices, n=1.73–2.63 at 600 nm . Weighted average reflectances of 6.5% (measured) and 7.0% (calculated) were achieved for TiO2 DLAR coatings in air and under glass, respectively. When implemented in a high-efficiency silicon solar cell, a short-circuit current density increase of Δ J sc =2.5 mA/cm 2 can be expected for an optimised TiO2 DLAR coating when compared to a commercial TiO2 single-layer antireflection coating.

Abstract Improved solar cell efficiency is the key to ongoing photovoltaic cost reduction, particularly as economies of scale propel module-manufacturing costs towards largely immutable basic material costs and as installation costs become an increasingly large contributor to total system costs. To enable manufacturers to move past the 20% cell energy conversion efficiency figure in production, high-efficiency PERC (Passivated Emitter and Rear Cell) sequences are being increasingly brought online. Most new photovoltaic manufacturing capacity added in the second half of 2014 was PERC-based, making PERC now the cell technology with second-highest production capacity, with the latest industry roadmap anticipating PERC will become the dominant commercial cell technology by 2020. The first paper describing the PERC cell appeared in 1989, although the structure was conceived several years earlier. The attractive technical features were the reduction of rear surface recombination by a combination of dielectric surface passivation and reduced metal/semiconductor contact area while simultaneously increasing rear surface reflection by use of a dielectrically displaced rear metal reflector. The key issues in the development of this technology and its commercial implementation are described, including a review of recent adoption rates and the way these are likely to evolve in the future.

AbstractOne way of improving the efficiency of solar cells is to subdivide the broad solar spectrum into smaller energy ranges and to convert each range with a cell of appropriately matched bandgap. The most common approach to implementing this idea has been to use a monolithic or mechanical stack of cells arranged in order of increasing bandgap, with the highest bandgap cell uppermost. This provides automatic filtering of incident sunlight so that each cell absorbs and converts the optimal spectral range. The potential of an earlier experimental approach based on steering light in different wavelength bands to non‐stacked cells recently has been re‐explored with good results. The present work extends this previous work by putting measurements on a more rigorous basis and by improving the ‘composite’ experimental efficiency of selected cells to beyond 43%, the highest reported to date for any combination of photovoltaic devices. Copyright © 2009 John Wiley & Sons, Ltd.

Abstract High efficiency commercial silicon solar cell technologies are often fabricated on n-type wafers to avoid light-induced degradation and other recombination centres that are observed in boron-doped Czochralski silicon. The advanced cell structures often feature the p–n junction on the rear of the device and require high bulk lifetimes in order to achieve high efficiencies. However n-type Czochralski silicon is still subject to a range of impurity related defects which can substantially reduce the lifetime of such material. In this work, large improvements in bulk lifetimes were demonstrated on standard commercial grade n-type Czochralski silicon from values in the range of 90–190 μs to values of 3.4–4.9 ms through the use of a short, low temperature hydrogen passivation process only using atomic hydrogen released from layers of silicon oxynitride grown by plasma enhanced chemical vapour deposition. The large improvements suggest that wafers with inherent low lifetimes, often deemed unsuitable to achieve high efficiencies, could in fact be compatible with the use of advanced cell architectures, to realise cell efficiencies over 24%. Oxygen precipitates are one type of impurity related defect which can cause substantial lifetime and efficiency limitations in both n- and p-type Czochralski silicon solar cells. An advanced hydrogenation process incorporating minority carrier injection was observed to lead to the complete electrical deactivation of the recombination activity of the defects. Furthermore, the passivation was retained throughout the remainder of the fabrication sequence and hence, no recombination activity from oxygen precipitates was evident on finished devices.

In this article, we investigate the extent of lifetime degradation attributed to light- and elevated-temperature-induced degradation (LeTID) in p- type multicrystalline silicon wafers passivated with different configurations of hydrogenated silicon nitride (SiNx:H) and aluminum oxide (AlOx:H). We also demonstrate a significant difference between AlOx:H layers grown by atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) with respect to the extent of LeTID. When ALD AlOx:H is placed underneath a PECVD SiNx:H layer, as used in a passivated emitter and rear solar cell, a lower extent of LeTID is observed compared with the case when a single PECVD SiNx:H layer is used. On the other hand, the LeTID extent is significantly increased when an ALD AlOx:H is grown on top of the PECVD SiNx:H film. Remarkably, when a PECVD AlOx:H is used underneath the PECVD SiNx:H film, an increase in the LeTID extent is observed. Building on our current understanding of LeTID, we explain these results with the role of ALD AlOx:H in impeding the hydrogen diffusion from the dielectric stack into the c-Si bulk, while PECVD AlOx:H seems to act as an additional hydrogen source. These observations support the hypothesis that hydrogen is playing a key role in LeTID and provide solar cell manufacturers with a new method to reduce LeTID in their solar cells.