We report on RISE-EWT (Rear Interdigitated Single Evaporation-Emitter Wrap-Through) solar cells on full area (12.5×12.5cm2) pseudo square boron doped Czochralski-grown silicon wafers. We investigate the main efficiency optimisation factors of these cells by investigating the dependence of RISE-EWT cell parameters on the base dopant concentration NA. We furthermore detail the effects of large feature sizes in base and emitter regions at the rear of the solar cell and investigate these effects with particular attention to the edge regions. EWT solar cells typically exhibit rather low fill factors. However, our results show that the improved fill factors can be achieved by increasing NA, which in return leads to optimised efficiency values. For our RISE-EWT solar cells made from boron doped Cz-Si wafers, this benefit is maintained even after light-induced degradation. Our investigation of edge area related effects shows the importance of proper cell design in these areas, leading to a further 2.8% absolute improvement in the fill factor. Combining increased base dopant concentration with optimised edge design, we achieve 19.0% efficiency on (12.5×12.5cm2) boron doped Cz silicon wafers before light-induced degradation, resulting in 18.1% efficiency in the light-degraded state.

The RISE-EWT (Rear Intendigitated Single Evaporation Emitter Wrap Through) solar cell is a silicon wafer-based solar cell concept that is capable of achieving solar energy conversion efficiencies of over 21%. The fabrication sequence is based exclusively on industrially feasible processing steps and avoids any photolithography and masking steps, nor does it require boron diffusion. For low process complexity, the RISE-EWT solar cell can be made with only a single phosphorus diffusion and a single evaporation step for metallisation. All structuring of the cell is based on non-contacting laser processing. Laser technology is the key tool for processing RISE-EWT solar cells: The cell has laser drilled and phosphorus-diffused holes to connect the emitter layer on the front side with the emitter and the contacts on the rear side. The emitter and base contact regions are defined by laser ablation of a diffusion barrier and KOH etch prior to phosphorus diffusion. An important feature of RISE-EVVT solar cells are steep surface features (flanks) that are produced by the laser ablation and KOH-etching. We use these flanks to achieve reliable separation between the contacts to the n-type polarity and to the P-type polarity of the solar cell. We provide a description of RISE-EWT manufacturing process and present an analysis of the recombination losses in our cells. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

We present a prototype of a new module assembly machine, which addresses five aspects of current fabrication issues: (i) Increase of module production speed for (ii) cells with both contacts on the rear side, (iii) use of lead free solders, (iv) reduction of cell handling and (v) applicability to thin solar cells. We name the prototype ATLAS. The ATLAS system lays up back contact cells directly onto the module lamination foil and solders the interconnectors to the cells using a laser. Our newly developed prototype system handles each cell only once. The problem of accumulation of particles in the soldering station is avoided as each new lamination sheet serves as a clean substrate. The system is capable of assembling back-contacted cells. Cell and cross connection is done in one machine. Our ATLAS prototype system solders a complete connector bone between two solar cells in 5 s with one 200 W diode laser and one handling system. For a production system the speed may easily be increased to 2 s per cell by using three diode lasers. Compared to a standard stringer, the ATLAS system concept will double the productivity.

We demonstrate mask-free fabrication of a 22.0%-efficient crystalline Si solar cell by applying laser ablation of Si and by laser ablation of protective coatings. The bulk absorber material is a p-type float zone silicon wafer and the designated cell area is 4 cm(2). While the processing time of our laboratory-type of laser system is far too slow for industrial processing, we estimate on the basis of our experiments that laser processing of 12.5 x 12.5 cm(2)-sized solar cells in just a few seconds is feasible with commercially available equipment. Copyright (c) 2006 John Wiley & Sons, Ltd.

Local contacts through dielectric layers are an important prerequisite for the production of very high efficiency SiO2-or SiNx-passivated silicon solar cells. We use laser ablation as a contactless process for local removal of dielectric layers. This contactless process is suitable for processing very thin wafers without cell breakage. Carrier lifetime measurements indicate that our laser ablation process produces no or only negligible damage to the silicon crystal. Open-circuit voltages of solar cells which were locally contacted through laser ablated SiNx underline the finding that the crystal damage is negligible. High fill factors and low series resistances of 0.6 Ohmcm2 reveal the successful local opening of the passivating dielectric layer. These properties qualify local laser ablation of passivating dielectric layers for the production of high-efficiency solar cells. In addition, the contactless nature of laser ablation makes this technique attractive for processing very thin silicon wafers

During the last years, the photovoltaic solar cell industry has experienced enormous growth. However, for solar cells to be competitive on the longer term, both an increase in their efficiency as well as a reduction in their cost is necessary. This paper discusses some opportunities of laser technology to realize these improvements.An effective method to reduce costs of silicon solar cells is reducing the wafer thickness, because silicon causes a large part of the costs. Consequently, for applying the emitter contact fingers on the solar cell, contact free laser processing has a large advantage in contrast to commonly used print screen techniques. This is because of less scrap due to broken wafers. Additional, many novel high efficiency solar cell concepts are only feasible with laser technology, e.g. due to the requirement for drilling a few thousand holes per second in brittle materials.In this paper, experimental investigations are discussed for producing grooves and holes in silicon wafers according to a recently developed solar cell concept. The amount of heat affected silicon in the surrounding of the processing is minimized. Any unavoidable heat affected material and debris is subsequently removed with a chemical etching process. Laser processing is studied with a variety of pulsed laser sources like excimer lasers, Nd:YAG lasers and frequency converted solid state lasers with a variety of wavelengths. Furthermore, different types of lasers are compared regarding their processing quality and processing time.

High-efficiency inversion-layer silicon solar cells are described where the contact to the inversion layer is made via a diffused p-n junction. Silicon nitride (SiN) films are deposited at 250°C or 375°C onto the front surface, resulting in strongly differing surface passivation and inversion-layer properties. A record-high open-circuit voltage for inversion-layer solar cells of 662 mV on 0.5 Ωcm float-zone p-silicon is obtained for the 375°C SiN films. The performance properties of these 16% efficient inversion-layer solar cells are analyzed by means of 2D numerical modeling. An analytical model is developed for the perimeter recombination current via the inversion-layer emitter. Good agreement between measured and simulated dark and 1-sun current-voltage curves is obtained, allowing for the determination of the dominant power and recombination losses in the experimental solar cells