Kristian Peter

Bifacial Solar Cells on Multi-Crystalline Silicon with Boron BSF and Open Rear Contact

The standard industrial multi-crystalline silicon (mc-Si) solar cell is monofacial and includes screen printed aluminum back surface field (BSF). A simple approach to increase performance and reduce costs per Wpeak is to collect the albedo on the rear side. In this work a bifacial, screen printed mc-Si solar cell with boron BSF is demonstrated. Rear to front efficiency ratios of up to 0.83 have been reached on 100times100mm2 mc-Si wafers with a thickness of about 200mum. The best solar cell processed so far with a boron BSF had an efficiency under front side illumination of eta=16.1% and a back to front efficiency ratio of 0.77. The possible gain in performance in later operation was estimated using PC1D simulation and depends on the albedo that is the amount of light that penetrates into the solar cell from the rear side. The simulation was confirmed by outside module tests, leading to an average gain of 19.5% over one day

Large Area Screen Printed N-Type MC-SI Solar cells With B-Emitter: Efficiencies Close to 15% and Innovative Module Interconnection

In this paper we present n-type Si solar cells on large area mc-Si wafers with a boron diffused emitter at the front side. The focus of our studies is mainly related to the front surface of the solar cell. We have optimised BBr3-diffusion and in-situ oxidation with respect to the homogeneity of the sheet resistance and substrate degradation. After diffusion even a slight improvement of the minority charge carrier lifetime was measured, which can be related to B-gettering. The emitter is contacted by AgAl-paste and passivated by thermal SiO2. The development and optimisation of all processes led to solar cells with efficiencies of 14.7% on mc-Si and 17.1% on Cz-Si substrates. In addition to this we present an innovative interconnection of modules using our developed cell (patent pending). We show an alternate serial interconnection of p- and n-type solar cells resulting in easier module processing

Over 18% Efficient MC-SI Solar Cells from 100% Solar Grade Silicon Feedstock from a Metallurgical Process Route

Based on very promising results for solar cells manufactured in an industrial process reaching 16% efficiency we analyzed if solar grade (SoG) silicon feedstock is capable to match up with electronic grade silicon in high efficiency ranges. Thus we applied a reliable lab-type process on 5times5 cm2 wafers resulting in 2times2 cm2 untextured solar cells with an efficiency limit of 18.5% for floatzone (FZ) references. The 5times5 cm2 wafers were selected out of 12.5times12.5 cm2 phosphorous pregettered SoG-Si wafers characterized by lifetime measurements. The best solar cell out of 100% Elkem SoG-Si reached eta=18.1% stable efficiency certified by FhG-ISE CalLab. This is the highest value for this material reported so far

Analysis of multicrystalline solar cells from solar grade silicon feedstock

The paper focuses on the analysis of solar cells from the newly developed solar grade silicon (SoG-Si) feedstock from a metallurgical process route. The emphasis of our experiments was to define an industrial solar cell process to achieve efficiencies higher than /spl eta/=16% on multicrystalline wafers containing a significant amount of the SoG-Si. The material was prepared as multicrystalline ingots by directional solidification and wafered by conventional wire saw technique. We demonstrate efficiencies higher than 16% on several wafers of 156 cm/sup 2/ size with an industrial process sequence from batches containing 25% and 65% Elkem SoG-Si feedstock. The new feedstock under investigation will enable the mass PV production and opens the route for cost reductions in the PV-industry.

A Process Design for the Production of IBC Solar Cells on Multi-Crystalline Silicon

In this paper we present a process for the fabrication of interdigitated back contact (IBC) solar cells on multi-crystalline silicon substrates. The process was tested on 1 Omegacm p-doped CZ wafers with a thickness of 180 mum. All process steps used were compatible with industrially established, low-cost production technologies. The process is designed to minimize thermal load on the wafers and is thereby well suited to multi-crystalline silicon substrates. The cell performance was limited by their fill factor due to incorrect firing parameters of the screen printed metallization

Realization of Thin MC-Silicon Pert-Type Bifacial Solar Cells in Industrial Environments

We present bifacial solar cells processed with a sequence suitable for industrial production. This method uses the LPCVD silicon nitride deposition based on DCS (dichlorosilane) or BTBAS (bis-(tertiary butyl amino)-silane). The bifacial solar cell process on wafers of 200 mum thickness has the following steps: (1) boron doped BSF of Rsheet =60 ohm/sq; (2) POCl3 emitter (on front side) of Rsheet= 50-55 ohm/sq; (3) thermal oxidation of the wafer surfaces; (4) the deposition of DCS or BTBAS based LPCVD silicon nitride on either sides of the wafer (5); finger grid printing on both sides and firing; (6) edge isolation. The solar cells produced with the DCS based silicon nitride process exhibit fill factor (FF) values of 76% on p-type and 75% on n-type solar cells with a rear to front efficiency ratio etarear/etafront of 67% for the p-type solar cells and 43% for the n-type solar cells. The solar cells with the BTBAS silicon nitride show FF values close to 72% and etarear/etafront 68% for p-type solar cells

Characterisation of LPE thin film silicon on low cost silicon substrates [solar cells]

Thin Si layers of 8-30 /spl mu/m were grown by LPE on upgraded metallurgical (UMG) multicrystalline Si substrates. A melt back step just before the growth process circumvented the additional supply of Si to the melt. Solar cells, realized by using a simple screenprinting process, reached efficiencies up to /spl eta/=6% (FF=74.1%, J/sub SC/=14.7 mA/cm/sup 2/, V/sub OC/=551 mV) without antireflection coating. The influence of impurity diffusion from the substrate into the active layer and the impurity incorporation from the In solution during the growth process have been studied (e.g. by SIMS). Using Secco etching, LBIC and spectral response measurements it could be shown that the local I/sub sc/ is not limited by impurities and further increases in l/sub sc/ could be achieved by growing thicker epilayers. The results of the investigations underline the good crystal quality of the epilayers on UMG Si substrates and enables the further increase of the efficiency.