A.W. Weeber

Interconnection through vias for improved efficiency and easy module manufacturing of crystalline silicon solar cells

It has become an opportune to develop new module technologies because manufacturers are using larger wafers leading to problems with interconnection of cells. ECN has developed a new cell and module design for crystalline silicon solar cells called pin-up module (PUM) based on old patents (Jong, US Patent 3,903,428, 1975; Pack, US Patent 3,903,427, 1975). In this design a limited number of holes serve as vias for interconnection of the front-side metallisation to a foil at the rear side by using pins. In this way the busbars at the front side are eliminated, thus reducing shadow losses. Calculations show that for 100 cm2 cells, the e

Industrially feasible >19% efficiency IBC cells for pilot line processing

ciency will be 0.4% absolute higher. For larger cells, the e

Molecular dynamics studies of the bonding properties of amorphous silicon nitride coatings on crystalline silicon

ciency gain will be as high as 1%. The PUM concept gives the possibility to increase cell dimensions without reducing the output. ( 2001 Elsevier Science B.V. All rights reserved.

Emission efficiency limit of Si nanocrystals

Interdigitated Back Contact (IBC) solar cells with >19% efficiencies have been fabricated using n-type silicon wafers and well-demonstrated high-volume solar cell process technologies alone. Excellent current collection is implied by Jsc values as high as 41.6 mA/cm2. High Pseudo Fill Factors (PFF) of above 81% and reduced Fill Factors (FF) of below 72%, suggest that the primary losses are due to series resistance. The process flow described is currently being transferred to a pilot production line for further process development.

The fundamental properties of SiN/sub x/:H that determine its passivating qualities

In this paper we present molecular dynamics simulations of silicon nitride, both in bulk and as an interface to crystalline silicon. We investigate, in particular, the bonding structure of the silicon nitride and analyze the simulations to search for defective geometries which have been identified as potential charge carrier traps when silicon nitride forms an interface with silicon semiconductors. The simulations reveal how the bonding patterns in silicon nitride are dependent upon the stoichiometry of the system. Furthermore we demonstrate how having an “interphase”, where the nitrogen content in silicon gradually reduces toward pure silicon across a boundary region, as opposed to an interface where there is an abrupt drop in nitrogen concentration at the boundary, can result in significantly different numbers of certain important carrier trap.

Crystalline silicon interconnected strips (XIS): Introduction to a new, integrated device and module concept

One of the important obstacles on the way to application of Si nanocrystals for development of practical devices is their typically low emissivity. In this study we explore the limits of external quantum yield of photoluminescence of solid-state dispersions of Si nanocrystals in SiO2. By making use of a low-temperature hydrogen passivation treatment we demonstrate a maximum emission quantum efficiency of approximately 35%. This is the highest value ever reported for this type of material. By cross-correlating PL lifetime with EQE values, we obtain a comprehensive understanding of the efficiency limiting processes induced by Pb-defects. We establish that the observed record efficiency corresponds to an interface density of Pb-centers of 1.3 × 1012 cm12, which is 2 orders of magnitude higher than for the best Si/SiO2 interface. This result implies that Si nanocrystals with up to 100% emission efficiency are feasible.

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

Structural properties of SiN/sub x/:H layers deposited with N/sub 2/+SiH/sub 4/ and NH/sub 3/+SiH/sub 4/ are related to the passivation properties. It is shown that the Si-N bond density in the layers is an important parameter for the passivation of mc-Si solar cells. The best bulk and thermally most stable surface passivation is observed for Si-N bond densities around 1.1/spl middot/10/sup 23/ cm/sup -3/. Lower bond densities result in a more open structure and will probably lead to H/sub 2/ formation during annealing. These H/sub 2/ molecules do not contribute to the passivation but will effuse from the layers into the ambient. Higher Si-N bond densities will result in too dense layers with a lower diffusivity of H and less bulk passivation during short anneals like contact firing. This explains why the bulk passivating properties of SiN/sup x/:H layers does not depend on the initial H concentration in those layers.

Excellent rear side passivation on multi-crystalline silicon solar cells with 20 nm uncapped Al 2 O 3 layer: Industrialization of ALD for solar cell applications

A new device concept for high efficiency, low cost, wafer based silicon solar cells is introduced. To significantly lower the costs of Si photovoltaics, high efficiencies and large reductions of metals and silicon costs are required. To enable this, the device architecture was adapted into low current devices by applying thin silicon strips, to which a special high efficiency back-contact heterojunction cell design was applied. Standard industrial production processes can be used for our fully integrated cell and module design, with a cost reduction potential below 0.5 €/Wp. First devices have been realized demonstrating the principle of a series connected back contact hybrid silicon heterojunction module concept.

Higher efficiency for thin multi crystalline silicon solar cells by improving the rear surface passivation

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.

Effect of EVA Encapsulation on Antireflection Properties of Mie Nanoscatterers for c-Si Solar Cells

Current bottlenecks for industrialization of Al2O3 deposited by Atomic Layer Deposition (ALD) for crystalline silicon solar cell applications are low growth rate and stability of thin and uncapped layers during co-firing. First results on the performance of a high throughput ALD proto-type, the Levitrack, are presented. Excellent passivation properties have been obtained after firing, for 12 nm thick films deposited on p-Cz (2.3 Ω.cm) with Seff <15cm/s (Δn=3×1015 cm−3). These layers are compatible with solar cells that operate at a maximum open-circuit voltage of 720mV. Furthermore, we report on the passivation of 20nm uncapped aluminum oxide layers on the rear of p-type mc-Si bifacial cells. LBIC measurements unveiled excellent passivation properties on areas covered by 20nm of Al2O3 characterized by an IQE of 91% at 980nm. Remarkably, these lifetime and cell results were obtained without lengthy post-treatments like forming gas anneal.