The interdigitated back contact (IBC) solar cells developed at the Australian National University have resulted in an independently confirmed (Fraunhofer Institut fur Solare Energiesysteme (ISE) CalLab) designated-area efficiency of 24.4 ± 0.7%, featuring short-circuit current density of 41.95 mA/cm2, open-circuit voltage of 703 mV and 82.7% fill factor. The cell, 2 × 2 cm2 in area, was fabricated on a 230 µm thick 1.5 Ω cm n-type Czochralski wafer, utilising plasma-enhanced chemical vapour deposition (CVD) SiNx front-surface passivation without front-surface diffusion, rear-side thermal oxide/low-pressure CVD Si3N4 passivation stack and evaporated aluminium contacts with a finger-to-finger pitch of 500 µm. This paper describes the design and fabrication of lab-scale high-efficiency IBC cells. Characterisation of optical and electronic properties of the best produced cell is made, with subsequent incorporation into 3D device modelling used to accurately quantify all losses. Loss analysis demonstrates that bulk and emitter recombination, bulk resistive and optical losses are dominant and suggests a clear route to efficiency values in excess of 25%. Additionally, laser processing is explored as a means to simplify the manufacture of IBC cells, with a confirmed efficiency value of 23.5% recorded for cells fabricated using damage-free deep UV laser ablation for contact formation. Meanwhile all-laser-doped cells, where every doping and patterning step is performed by lasers, are demonstrated with a preliminary result of 19.1% conversion efficiency recorded. Copyright © 2014 John Wiley & Sons, Ltd.

Design, fabrication and characterisation of a 24.4% efficient interdigitated back contact solar cell

The current cost distribution of a crystalline silicon PV module is clearly dominated by material costs, especially by the costs of the silicon wafer. Therefore cell designs that allow the use of thinner wafers and the increase of energy conversion efficiency are of special interest to the PV industry. This article gives an overview of the most critical issues to achieve this aim and of the recent activities at Fraunhofer ISE and other institutes.

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High-Efficiency Crystalline Silicon Solar Cells

A solar cell and a method for manufacturing the same are disclosed. The solar cell includes a substrate of a first conductive type, an anti-reflection layer that is positioned on the substrate and is formed of a transparent conductive oxide material, a plurality of emitter layers on the substrate, the plurality of emitter layers being of a second conductive type opposite the first conductive type, a plurality of first electrodes on the plurality of emitter layers, and a plurality of second electrodes that are electrically connected to the substrate and are positioned to be spaced apart from the plurality of first electrodes. The first electrodes and the second electrodes are positioned on the same surface of the substrate.

Solar cell and method for manufacturing the same

20.8% industrial PERC solar cell: ALD Al2O3 rear surface passivation, efficiency loss mechanisms analysis and roadmap to 24%

A review of interconnection technologies for improved crystalline silicon solar cell photovoltaic module assembly

For an alternative front side metallization process without screen printing of metal paste the selective opening of the front surface anti-reflection coating could be realized by laser ablation. A successful implementation of this scheme requires direct absorption of the laser light within the anti-reflection coating, since the emitter underneath must not be damaged severely. Additionally, the ablation must be feasible on textured surfaces. In this paper, we show that laser light with a wavelength of 355 nm and a pulse length of approximately 30 ns is absorbed directly by a typical silicon nitride anti-reflection coating. Based on lifetime measurements on ablated samples it is shown that a damage free laser ablation of SiNx layers on planar surfaces is possible. The characteristic ablation structure on textured surfaces is explained and quantified by rigorous coupled wave analysis (RCWA) simulations. Finally, high efficiency solar cells with a standard emitter (Rsh approx. 50 Ω/sq) have been processed using laser ablation of the silicon nitride anti-reflection coating. These cells show efficiencies of up to 19·1%, comparable to the reference solar cells using photolithographically opened contact areas. Copyright © 2008 John Wiley & Sons, Ltd.

Selective Laser Ablation of SiNx Layers on Textured Surfaces for Low Temperature Front Side Metallizations

Fraunhofer ISE's concept for an advanced metallization of silicon solar cells is based on a two-step process: the deposition of a seed layer to form a mechanical and electrical contact and the subsequent thickening of this seed layer by a plating step, preferably by light-induced plating (LIP). The concept of a multi-layer metallization is used for most of the relevant high-efficiency cell types in industry. The main advantage of this concept is that each layer can be optimized individually, i.e. the seed layer to achieve an optimal electrical and mechanical contact and the plated layer in terms of high lateral conductivity and good solderability. Solar cells results with seed layers fabricated by aerosol printing, chemical Ni plating on cells with a laser-structured dielectric layer and laser-enhanced Ni plating are presented.

Progress in advanced metallization technology at Fraunhofer ISE

This paper presents the results of a seed and plate technology, based on electroless nickel plating on industrial substrates. Through the photoassisted surface activation of the cells homogeneous NiP coatings, about 30-50 nm thick have been deposited. The combination of this step with inkjet masking and etching has been compared with laser ablation and with standard screen printed cells on industrial solar cells. An improvement of 0.5% absolute in efficiency has been achieved thanks to the use of nickel contacts. The advantages and disadvantages of each structuring process are introduced. The evaluation of the laser ablation + nickel process on high efficiency structures has delivered FF over 80%.

Advances in Electroless Nickel Plating for the Metallization of Silicon Solar Cells Using Different Structuring Techniques for the ARC

To reduce shadowing losses and therefore gain higher short current densities JSC as well as to overcome contact resistance limitations a front side metallization based on laser ablation of the antireflection coating and plated contacts is proposed. In this paper we will present solar cells with efficiencies of up to 20.7 % featuring an industrially feasible shallow diffused 110 Ohm/sq. emitter and a plasma enhanced chemical vapour deposition (PECVD)-SiN antireflection coating. The main focus in this paper lies on the laser ablation process. The characteristics of ns- and ps-laser ablation regarding the influence on the emitter profile and the ablation pattern on a textured surface will be discussed.

Laser ablation of antireflection coatings for plated contacts yielding solar cell efficiencies above 20

Laser processes have penetrated into the crystalline silicon solar cell production market some time ago already, but are
still far from reaching the status they probably will achieve one day. As the largest fraction of state-of-the-art production
lines still produces conventional screen-printed aluminum back surface field (Al-BSF) cells, the applicability of lasers is
currently limited mainly to the process step of laser edge isolation, while only a few other companies use lasers for
groove formation (fabrication of laser grooved buried contact solar cells) or via hole drilling. Due to the
contactless nature as well as the possibility to process a wide variety of materials with fine structures, lasers can be used
for a vast field of production steps like ablating, melting and soldering different materials. Within this paper several
applications of laser processes within the fabrication of various next-generation silicon solar cell structures are presented.
These processes are for example laser via hole drilling, which is inevitable for MWT and EWT (metal and emitter wrap
through) solar cells, LFC (laser-fired contacts) as a fast and easy approach for the production of passivated emitter and
rear solar cells as well as laser ablation of dielectric layers and laser doping which offer the chance for industrial
production of several different high efficiency solar cell structures.

Annerose Knorz

Papers

Selective Laser Ablation of SiNx Layers on Textured Surfaces for Low Temperature Front Side Metallizations

Progress in advanced metallization technology at Fraunhofer ISE

Advances in Electroless Nickel Plating for the Metallization of Silicon Solar Cells Using Different Structuring Techniques for the ARC

Laser ablation of antireflection coatings for plated contacts yielding solar cell efficiencies above 20

Novel laser technologies for crystalline silicon solar cell production