Jozef Szlufcik

Advanced manufacturing concepts for crystalline silicon solar cells

An overview is given concerning current industrial technologies, near future improvements and medium term developments in the field of industrially implementable crystalline silicon solar cell fabrication. The paper proves that considerable improvements are still possible, both in efficiency and in production cost. The paper also proves that a lot of effort is being put worldwide on thinner substrates and on thin-film crystalline silicon cells deposited on cheap carriers, in order to save in substrate cost and in order to gain more independence from availability problems of silicon feedback.

Efficiency improvement by porous silicon coating of multicrystalline solar cells

Abstract Shallow junction multicrystalline Si solar cells have been processed by an anodical etching technique. More than 25% improvement in short-circuit current and photovoltaic energy conversion efficiency was demonstrated. It was shown that improved performance was caused by antireflection action of the porous silicon layer as well as by the cell surface and grain boundary passivation.

High-efficiency low-cost integral screen-printing multicrystalline silicon solar cells

This paper describes how the efficiency and throughput of industrial screen-printed multi-Si solar cells can be increased far beyond the state-of-the-art production cells. Implementation of novel processes of isotropic texturing, shallow emitter or single diffusion selective emitter, combined with screen-printed metallization fired through a PECVD SiNx ARC layer, have been described. Novel dedicated fabrication equipment for emitter diffusion and a PECVD SiNx deposition system are developed and implemented thereby removing the processing bottlenecks linked to the diffusion and bulk passivation processes. Several types of back-contacted solar cells with improved visual appeal required for building integrated photovoltaic (BIPV) application have been developed.

Record high performance modules based on screen printed MWT solar cells

This paper describes an integrated approach towards the realisation of modules based on rear contacted solar cells joining experiences in cell and module manufacturing. While research is ongoing on novel interconnection schemes, from an analysis of different possibilities, a methodology was selected that allows the introduction of the interconnection approach within a production line with minor investments. To support the suggested methodology a number of structural changes were required in the Metallisation Wrap Through cells. However, as these were limited to the layout of the contact pattern, no changes to the established cell process were needed except for the introduction of new screens. Based on the developed simple planar interconnection technology, a number of modules was manufactured with large area (100cm/sup 2/) multi-crystalline rear contacted solar cells demonstrating the electrical added value of rear contacted solar cells and attaining power densities of over 145 W/m/sup 2/.

Industrial PERL-Type Si Solar Cells With Efficiencies Exceeding 19.5%

In this paper, we describe a path toward industrial passivated emitter, rear locally diffused (PERL)-type crystalline Si solar cells with efficiencies exceeding 19.5%. The impact of thickness and quality of different local back surface field (BSF) pastes on the extended laser ablation (ELA) rear contacting technique is investigated, and the effect of the wafer resistivity and emitter diffusion/oxidation processes on cell performance is evaluated. Based on these investigations, an optimized process flow for PERL-type monocrystalline Si solar cells is defined, and its capability is tested against that of standard Al-BSF in large batch experiments, demonstrating a top efficiency of 19.7%, a 19.5% average efficiency, and an efficiency increase of about 1% abs. with respect to Al-BSF cells.

IIb-2 – Low Cost Industrial Technologies of Crystalline Silicon Solar Cells

Publisher Summary This chapter discusses industrial technologies for manufacturing crystalline silicon solar cells at low costs. Typical efficiency of commercially produced crystalline silicon solar cells lies in the range of 14%–17%. Because the efficiency of the cell influences the production cost at any production stage, considerable efforts are directed toward efficiency improvement of solar cells. The required near future efficiency goals for industrial cells are 18–20% on monocrystalline, and 16–18% on multicrystalline silicon. Based on laboratory scale achievements, one can consider that production type cells able to fulfill the efficiency goal should have features including front surface texturing, optimized emitter surface concentration and doping profile, effective front surface passivation, fine line front electrode, and front electrode passivation. This chapter discusses the concepts of cell processing, substrates, etching, texturing, optical confinement, and junction formation in detail. It then explains front surface passivation and functions of antireflection coating. Techniques of gettering by phosphorous diffusion and gettering by aluminum treatment are also discussed. Concepts related to screen-printed solar cells, buried contact solar cells, solar cells on silicon ribbons, and back-contacted solar cells are explained in detail in the chapter.

Chapter IB-3 – Low-Cost Industrial Technologies for Crystalline Silicon Solar Cells1

Publisher Summary Silicon substrates used in commercial solar cell processes contain a near-surface saw-damaged layer, which has to be removed at the beginning of the process. Thickness of the damage depends on the technique used in wafering of the ingot. A layer with thickness of 20 to 30 μm has to be etched from both sides of wafers cut by an inner-diameter blade saw, while only 10 to 200 μ m is enough when a wire saw is used. The etching process has to be slightly modified when applied to multicrystalline substrates. Too fast or prolonged etching can produce steps at grain boundaries. This can lead to problems with interruptions of metal contacts. This problem can be avoided by an isotropic etching based on a mixture of nitric, acetic, and hydrofluoric acids. However, a strong exothermic reaction makes this etching process difficult to control and toxicity of the solution creates safety and waste disposal problems. The silicon surface after saw damage etching is shiny and reflects more than 35% of incident light. The reflection losses in commercial solar cells are reduced mainly by random chemical texturing. Surface texturing reduces the optical reflection from the single crystalline silicon surface to less than 10% by allowing the reflected ray to be recoupled into the cell.

IIb-2 – Low cost industrial technologies of crystalline silicon solar cells

Publisher Summary This chapter proposes a cheap and good-quality solar-grade polysilicon feedstock material to increase the sizes of substrates, to reduce the kerf loss in slicing, and to decrease the thickness of the substrates below 200 μm. Silicon substrates used in commercial solar cell processes contain a near-surface saw-damaged layer, which has to be removed at the beginning of the process. The thickness of the damaged layer depends on the technique used in wafering of the ingot. The silicon surface after saw-damage etching is shiny and reflects more than 35% of incident light. An important step in solar cell processing therefore consists of texturing the front surface—to create a structure that causes reflected rays to get a second chance to be coupled into the cell. The reflection losses in commercial solar cells are reduced mainly by random chemical texturing. Monocrystalline silicon substrates with a surface orientation can be textured by anisotropic etching at temperature of 70–80℃ in a weak solution of sodium hydroxide or potassium hydroxide with addition of isopropanol.

Crystalline silicon based photovoltaics: technology and market trends

An overview is given concerning industrial technologies, IMECSs advanced pilot line crystalline silicon solar cell technologies and medium term developments for industrial crystalline silicon terrestrial solar cell fabrication. Also IMECs work on thin film crystalline silicon solar cells is shortly presented, all of this taking into account the existing market and technology trends.

Evidence of TiOx reduction at the SiOx/TiOx interface of passivating electron-selective contacts

A TiOx layer is well known as an electron-selective contact material because of its asymmetric band offsets with respect to c-Si. When applying TiOx layers as passivating electron-selective contacts, forming sub-stoichiometric TiOx is important to obtain a low contact resistivity because oxygen vacancies increase the conductivity of TiOx and provide n-type doping effects. In this work, oxygen vacancies at SiOx/TiOx interfaces are investigated by atomic depth profiling of XPS measurements. Three kinds of TiOx layers are studied grown by either e-beam evaporation, atomic layer deposition or sputtering on c-Si. In all three TiOx samples, a resulting stack of c-Si/SiOx/TiOx could be noticed XPS measurements that show SiOx peaks near the c-Si/TiOx interface. Moreover, clear TiO2 peaks, which can be measured at the surface of all three TiOx layer types, gradually change to Ti or TiSi2 peaks near the SiOx/TiOx interface. This indicates that many oxygen vacancies seem to exist at the SiOx/TiOx interface. This TiOx reduction may contribute to the formation of a dipole and increased downward band bending resulting in a lower contact resistivity in the electron-selective contacts. As a result, hetero-junction solar cells with i-a-Si:H/TiOx/Ca/Al contacts exhibit a significant series resistance reduction of about 40 % compared to solar cells with i-a-Si:H/Ca/Al contacts.A TiOx layer is well known as an electron-selective contact material because of its asymmetric band offsets with respect to c-Si. When applying TiOx layers as passivating electron-selective contacts, forming sub-stoichiometric TiOx is important to obtain a low contact resistivity because oxygen vacancies increase the conductivity of TiOx and provide n-type doping effects. In this work, oxygen vacancies at SiOx/TiOx interfaces are investigated by atomic depth profiling of XPS measurements. Three kinds of TiOx layers are studied grown by either e-beam evaporation, atomic layer deposition or sputtering on c-Si. In all three TiOx samples, a resulting stack of c-Si/SiOx/TiOx could be noticed XPS measurements that show SiOx peaks near the c-Si/TiOx interface. Moreover, clear TiO2 peaks, which can be measured at the surface of all three TiOx layer types, gradually change to Ti or TiSi2 peaks near the SiOx/TiOx interface. This indicates that many oxygen vacancies seem to exist at the SiOx/TiOx interface. This TiO...