Markus Spiegel

Mechanically V-textured low cost multicrystalline silicon solar cells with a novel printing metallization

Results of our high throughput mechanical texturization technology suitable for highly efficient multi Si solar cells are addressed. In this work different structuring tool designs have been investigated for implementation in a low cost screen printing multi Si solar cell process. The benefit of the mechanical texturization on the cell performance is shown in experiment and simulation before and after encapsulation. As a further topic, results of multicrystalline solar cells metallized with a novel printing method-the roller printing technique-are shown. It is based on self-aligned mask-free roller printing of metal, dopant or masking pastes on protruding regions of V-grooved silicon solar cells.

Systematic study towards high efficiency multicrystalline silicon solar cells with mechanical surface texturization

The aim of the present work was to optimize a high efficiency process for multicrystalline silicon solar cells (including Al-gettering, oxide and hydrogen passivation, Al-BSF formation, photolithographically defined front metallization) and combine it with the mechanical texturization technique. New cell structures were created, in which only the areas between the front grid are V-grooved. Solar cells were processed on various ribbon and conventional cast silicon materials. IV-characteristics, reflectance and spectral response were measured and analysed by two dimensional device simulation. A comparison with equally processed flat cells shows an increase of cell efficiencies by more than 25% due to the reduction of optical losses before antireflection coating and by an additional 4% due to the enhanced collection probability in the V-groove volumes.

Separation of bulk diffusion length and back surface recombination velocity by improved IQE-analysis

Key parameters for the quantification of minority carrier recombination in solar cells are the effective bulk diffusion length, the bulk diffusion length and the back surface recombination velocity. As wafer thickness decreases and bulk quality increases the simultaneous determination of these parameters gains importance for cell process optimization in PV industry. Methods for obtaining these parameters have been described in the literature, such as the linear approximation on the inverse IQE vs. light penetration depth. We will formulate the limitations of this approach using numerically and experimentally determined IQE-data. The ambiguity of the older approach is solved by an improved equation, making it possible to obtain these parameters from a fit on the IQE within 820-940 nm. In addition an equation incl. the loss in the emitter is presented. Both methods are ideally suited for fast LBIC scan evaluations.

Implementation of hydrogen passivation in an industrial low-cost multicrystalline silicon solar cell process

The aim of this study was the incorporation of the microwave induced remote hydrogen plasma (MIRHP) passivation into a screen-printed solar cell process using different multicrystalline silicon base materials (BAYSIX (Bayer), Eurosil (Eurosolare), EMC (Sumitomo Sitix)). MIRHP before cell metallization including an antireflection coating (APCVD TiO/sub 2/ or PECVD SiN) as a capping layer to avoid the out-diffusion of hydrogen during contact firing as well as the MIRHP after cell metallization on uncoated cells have been investigated. As a reference, solar cells were processed without a MIRHP passivation. Using a PECVD SIN ARC on high quality material such as EUROSIL and BAYSIX an increase in the short circuit current density of 0.7 mAcm/sup -2/ and in the open circuit voltage of 3-4 mV have been observed by comparing cells with and without MIRHP. Using an APCVD TiO/sub 2/ ARC on solar cells based on EMC resulted in an increase in the short circuit current density of 0.7 mAcm/sup -2/ due to the MIRHP.

Investigations on hydrogen in silicon by means of lifetime measurements

Various techniques (SIMS, thermal effusion, FTIR) have been suggested for the determination of the diffusion of hydrogen in multicrystalline silicon. However these methods are either laborious or of a minor accuracy. Our work concentrates on the determination of hydrogen passivation depths in mc-Si by determining the minority carrier lifetime as a function of hydrogen passivation time. For the investigations EMC silicon and reference FZ silicon wafers have been used. From experimental data the passivation depth is obtained numerically using the simulation software PC1D and analytically using a simplified equation. For EMC, passivation depths in regions of good and poor quality have been obtained indicating no significant influence on the passivation depth. Further experiments by polishing the wafer prior to lifetime measurements with a small angle have been performed for determination of the SRV.

Roller printed multicrystalline silicon solar cells with 16% efficiency and 25 /spl mu/m finger width

The authors present results on multicrystalline silicon solar cells metallized by the novel roller printing technique. An efficiency of 16.3% has been achieved on 10/spl times/10 cm/sup 2/ Baysix multicrystalline silicon in a low cost process, applying a homogeneous 35 /spl Omega//sq emitter. The roller printed fingers show excellent properties, namely an optical finger width of 25 /spl mu/m, leading to a total finger shadowing of only 1.5%. Due to nonoptimal contact resistances the mean value of the fill factor of the roller printed cells is only about 73%. Device simulations predict for roller printed cells with low contact resistances and an optimized finger spacing a cell efficiency of 16.8% and an efficiency gain of 0.7% over screen printed cells. On a 50 /spl Omega//sq emitter even a 17% cell efficiency seems to be achievable after optimization of the firing conditions.