Showing papers by "Stefan W. Glunz published in 2000"

Overview of light degradation research on crystalline silicon solar cells

Abstract: Recent research on light degradation of crystalline Si materials and solar cells is reviewed. The first paper on the issue was published in 1973 when efficiency of solar cells using 1 Ω cm, B-doped CZ wafers degraded under illumination and recovered by annealing at a low temperature of around 200°C. In the 1990's, several studies have been performed to investigate the mechanism of the light degradation and also to provide practical solutions to suppress the degradation. Numerous experiments have been carried out regarding the effects of impurities including B, Ga, P, O and processing parameters such as oxidation temperature. To suppress the degradation, reducing the concentration of B and O or substituting boron by gallium as dopant was found to be effective. These findings are in agreement with a model attributing the lifetime degradation to oxygen and boron. Copyright © 2000 John Wiley & Sons, Ltd.

Laser ablation - a new low-cost approach for passivated rear contact formation in crystalline silicon solar cell technology

Abstract: The ablation of passivating layers using laser radiation offers a new way of defining the rear contact pattern for the passivated emitter and rear cell (PERC) concept. The KrF-Excimer laser has been identified to be a suitable tool for the ablation process. The laser process has been optimised in order to realise well-defined and shallow holes in silicon dioxide and silicon nitride using excimer laser ablation. Solar cell efficiencies of up to 20.4% and 19.7%, respectively have been realised by applying this process to the RP-PERC cell concept without using any laser-damage etching. Process times below 3 s can be realised for enhanced use of beam power using a microlens array. The process can be fully integrated in a vacuum process for rear contact formation. The laser ablation approach seems to offer a bright perspective of highly efficient rear contact formation for future thin and large solar cells. (orig.)

New simplified methods for patterning the rear contact of RP-PERC high-efficiency solar cells

Abstract: New processing schemes for fabricating the rear contact pattern of the PERC-structure (passivated emitter and rear cell) are demonstrated. Both, thermally-grown silicon oxide (SiO/sub 2/) and plasma-deposited silicon nitride (SiN/sub x/) are used as the passivating rear layer. The first processing scheme utilizes plasma etching of the dielectric layer through a mask. The plasma process was optimized in order to reduce the damage in the silicon base of the cell. Efficiencies of 21.5% and 21.7% have been achieved for SiN/sub x/ and SiO/sub 2/ rear layers, respectively. The second approach uses a laser beam to remove the dielectric layer for the rear contact pattern. Efficiencies of 19.7% and 21.3% have been achieved for SiN/sub x/ and SiO/sub 2/ rear layers, respectively. Reference cells with the same front structure but conventionally processed rear (photo resist, wet-chemical etching) show only a slightly higher efficiency of 22.0% on cells with a SiO/sub 2/ passivation layer. This proves that both approaches have a very high potential.

Verfahren zur herstellung eines halbleiter-metallkontaktes durch eine dielektrische schicht

Abstract: Beschrieben wird ein Verfahren zur elektrischen Kontaktierung einer, mit wenigstens einer dielektrischen Schicht (12) uberzogenen Halbleiterschicht (13). Die Erfindung zeichnet sich dadurch aus, dass eine Metallschicht (11) auf die dielektrische Schicht (12) aufgebracht wird und mittels einer Strahlungsquelle (9) diese Metallschicht (11) kurzzeitig lokal punkt- oder linienformig derart kontrolliert erhitzt wird, so dass sich eine lokale Schmelzmischung ausschliesslich aus der Metallschicht (11), der dielektrischen Schicht (12) sowie der unmittelbar unter der dielektrischen Schicht (12) befindlichen Halbleiterschicht (13) ausbildet, die nach dem Erstarren zu einem elektrischen Kontakt zwischen der Halbleiterschicht (13) und der Metallschicht (11) fuhrt.

100 cm2 solar cells on Czochralski silicon with an efficiency of 20·2%

Abstract: A solar cell process optimized for oxygen-contaminated silicon was used to fabricate 10 × 10 cm 2 cells on gallium-doped p-type Czochralski (Cz) silicon. An independently confirmed record efficiency of 20.2% was achieved. Although the material used contains a significant concentration of interstitial oxygen, no illumination-induced degradation of the cell parameters was observed. This is in excellent agreement with the observation that the metastable defect underlying the minority carrier lifetime is correlated with oxygen and boron. Thus, using gallium instead of boron as the dopant for p-type Cz silicon is an appropriate way to avoid the carrier lifetime degradation which is observed in boron-doped oxygen-contaminated Cz-Si.

Investigation of carrier lifetime in p-type Cz-silicon: specific limitations and realistic prediction of cell performance

Abstract: Recent studies have revealed that the metastable defect causing the lifetime degradation in standard boron-doped Czochralski silicon (B-Cz-Si) is correlated with boron and oxygen. This is confirmed by the authors' results from a comprehensive investigation of carrier lifetime in p-type Cz-Si. While no degradation and excellent lifetimes close to the theoretical limit are observed for all gallium-doped samples, the stable degraded lifetime of the B-Cz-Si samples is strongly reduced by the Cz-specific defect. In order to allow realistic simulations of cells from B-Cz-Si, the measured doping dependence of the bulk lifetime in B-Cz-Si is modeled by a simple empirical expression. It is demonstrated that the optimal doping concentration leading to maximum efficiency is strongly shifted with the used solar cell structure and the actual degradation state. While the maximum stable efficiency for a high efficiency RP-PERC solar cell is predicted for a base doping of 5.10/sup 15/ cm/sup -3/ using B-Cz-Si, the optimal value for an industrial cell with screen printing emitter varies between 10/sup 15/ cm/sup -3/ for a cell with boron BSF and 10/sup 16/ cm/sup -3/ for a cell without BSF. The physical background leading to these optima is discussed in detail. Finally, the authors verified the theoretical predictions for the high efficiency cell structure fabricating RP-PERC cells on B-Cz-Si.

Analysis of rear contacted solar cell structures for cost-effective processes and materials

Abstract: The authors compare the limiting effects of high-efficiency rear contacted solar cells, screen-printed rear contacted solar cells and emitter-wrap-through solar cells for different cell thickness by means of numerical device simulation. For high diffusion lengths, the high-efficiency rear contacted cell and the emitter-wrap-through solar cell show a decreasing short circuit current density with decreasing cell thickness, whereas the screen-printed rear contact cell shows the reverse behavior due to a "pumping" effect of the floating emitter. The impact of the emitter sheet resistance in the via hole of the emitter-wrap-through cell on the illuminated IV-curve is investigated for illumination from the front and from the rear side. The presented analysis allows an optimization of rear contacted cells for application as high-efficiency and as low-cost structures.

Highly efficient 115‐μm‐thick solar cells on industrial Czochralski silicon

Abstract: Thin solar cells on industrial Czochralski-material were produced and analyzed. For the Random Pyramid-Passivated Emitter and Rear Cell (RP-PERC) with planar rear surface, a maximum efficiency of near 20% was achieved for 115 as well as 165 μm thickness. In comparison, cells textured at the rear surface with a standard industrial process reached about a 2% (absolute) lower efficiency. This difference is consistently explained by an increased rear surface recombination, whereas light trapping properties are excellent for both rear surface treatments. The Cz-specific light-induced degradation of the thin cells is investigated.

Strategies for improving the efficiency of Cz-silicon solar cells

Abstract: Recent investigations have firmly established that the metastable defect which is responsible for the light-induced degradation in Czochralski silicon (Cz-Si) is correlated with oxygen and boron. Thus, an attractive way to improve the material quality is to substitute boron by gallium as the p-type dopant. The authors have verified that no degradation and excellent carrier lifetimes close to the theoretical limit are observed over a wide doping concentration range. Stable efficiencies higher than 20% can be achieved with an RP-PERC cell structure on gallium-doped Cz-Si with resistivities from 0.12 /spl Omega/ cm to 1.5 /spl Omega/ cm. A maximum efficiency of 22.2% was obtained at 0.3 /spl Omega/ cm despite the Ga-doped Cz-Si having a significant concentration of interstitial oxygen. Standard Cz-Si (boron-doped, oxygen-contaminated) can be improved by an optimized high-temperature step without external gettering. Choosing the optimal process parameters, it is possible to increase the stable lifetime significantly in both conventional tube furnace and rapid thermal processing (RTP) system. Using the RTP system, the stable lifetime can be improved by a factor of two within 120 s.

Prospects for high efficiency silicon solar cells in thin Czochralski wafers using industrial processes

Abstract: Lower PV systems cost can be achieved if less silicon material is used in modules and if higher solar cell efficiencies can be achieved cost effectively. In this study the efficiency limits of mass production high efficiency laser grooved buried grid solar cells have been modelled for thinner and thinner wafers. PC1D modelling has been coupled with a 3D ray tracing simulation RAYN to predict cells performance. Given suitable surface passivation, light trapping and minority carrier lifetime, solar cell efficiency can actually increase with decreasing wafer thickness. Cells were made by the RP-PERC process, using thinned industrial grade Czochralski silicon wafers. Cells (4cm/sup 2/) of over 20% efficiency were fabricated in wafers with a final thickness of 115 /spl mu/m. Standard production LGBG cells had poor BSFs but on process optimisation nearly 17% efficiency were made in 140 /spl mu/m micron wafers on an industrial production line.

Method and device for electrically contacting a material surface which is coated with at least one dielectric layer

Abstract: The invention relates to a method and a device for electrically contacting a material surface which is coated with at least one dielectric layer. The invention is characterised in that light from a light source is directed onto an arrangement consisting of a number of optical microlenses that are arranged in an array and through which the light is directed onto the dielectric layer; and in that a liquid or viscous medium is introduced between the arrangement consisting of the number of optical microlenses that are arranged in an array and the dielectric layer. This layer is essentially transparent to the light of the light source and material is removed locally from the dielectric layer through the specific illumination thereof until the material surface is exposed locally, respectively. The invention is also characterised in that metallisation takes place through the dielectric layer at the points where the material surface has been locally exposed, starting from the material surface.

Verfahren sowie eine vorrichtung zur elektrischen kontaktierung einer mit wenigstens einer dielektrischen schicht überzogenen materialoberfläche

Abstract: Beschrieben wird ein Verfahren sowie eine Vorrichtung zur elektrischen Kontaktierung einer mit wenigstens einer dielektrishen Schicht uberzogenen Materialoberflache. Die Erfindung zeichnet sich dadurch aus, dass Licht einer Lichtquelle auf eine Anordnung gerichtet wird, die aus einer Vielzahl, arrayformig angeordneter optischer Mikrolinsen besteht, durch die das Licht auf die dielektrische Schicht gerichtet wird, dass zwischen der, aus einer Vielzahl arrayformige angeordneter optischer Mikrolinsen bestehenden Anordnung und der dielektrischen Schicht ein flussiges oder viskoses Medium eingebracht wird, das weitgehend transparent fur das Licht der Lichtquelle ist, dass durch gezielte Belichtung der dielektrischen Schicht Material der dielektrischen Schicht lokal abgetragen wird, bis die Materialoberflache jeweils lokal freigelegt wird, und dass an den Stellen der lokal freigelegten Materialoberflache eine Metallisierung ausgehend von der Materialoberflache durch die dielektrische Schicht hindurch erfolgt.