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33rd European Photovoltaic Solar Energy Conference and Exhibition; 418-423, We present 6-inch bifacial p-type Czochralski-grown silicon passivated emitter and rear locally-diffused (PERL) solar cells with “pPassDop” layer stack on the cell’s rear side. The “pPassDop” layer stack consists of an aluminum oxide and a boron-doped silicon nitride layer serving as both surface passivation and doping source. Local laser processing introduces boron and aluminum atoms from the “pPassDop” layer stack into the silicon. The electrical contacting of the formed line-shaped p-doped back surface field is realized by screen-printed and fired pure silver contacts (i.e. without aluminum). The fabricated PERL solar cells reach high bifaciality of up to 89%. The monofacial peak front side energy conversion efficiency, measured with contact bars on both sides on a black non-conducting chuck, is given by 19.8%. Fill factors of more than 79% and specific contact resistances in the single-digit mΩcm²- range prove the successful low-resistance contacting on both sides. It is important to stress that the same commercial state-of-the-art firing-through pure silver screen-printing paste is used for the cell’s front and rear side metallization. A special alignment procedure ensures that the rear silver grid with finger widths of about 65 μm is placed over the whole wafer on top of the about 37 μm-wide laser-doped and opened structures.

26th European Photovoltaic Solar Energy Conference and Exhibition; 1089-1093, Most high-efficiency concepts for silicon solar cells utilise passivated surfaces and/or novel metallisation approaches. For these devices an anneal step, preferential in forming gas ambient, is beneficial or even crucial. Annealing is known to activate or improve surface passivation, facilitate metal-silicide formation, improve adhesion of metal contacts and cure potential crystal damage. Challenges for industrial solutions of anneal processes are a precise control of the process atmosphere and temperature, as well as a high throughput and easy integration into production lines. We present a high capacity inline annealing system that addresses these tasks with a throughput of over 1000 wafers per hour. The gas locks, located at the entrance and exit of the furnace, allow for an effective separation of laboratory and forming gas process ambient, which results in a residual oxygen concentration of a few ppm. Inline annealed silicon solar cells with a thermal oxide passivated rear surface show the same conversion efficiency as reference cells, which are annealed in a single wafer reactor. The specific cost of inline annealing in forming gas is calculated to be below 1.1 €ct/Wp.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1162-1166, The integrated project (IP) Crystal Clear has been finalized in June 2009 and thus a chapter of more than 5 years successful collaboration between European solar cell research institutes and industry is closed. This paper reviews the achievements within the 4th subproject (SP4) of Crystal Clear dealing with the development of advanced solar cell concepts. Within SP4, 12 of the 16 partners have participated and have formed a productive consortium. The goal of this subproject was the further reduction of the cell production costs to enable the psychological important Si PV module price below 1 Euro/Watt. This should be reached by novel cell designs and manufacturing processes in order to achieve a process cost reduction of 40% (cost per Wp). One major effort was put in the development of novel cell concepts and processes suited for thin wafers in industrial fabrication. Three cell concepts were distinguished and developed by the participating institutes: i-PERC, MWT with full Al, and solar cells with laser fired contacts (PERC-LFC). In addition to the effort to implement these concepts into an industrial type of process with large area wafers, excellent results have been achieved on EFG and RGS ribbons. World record results with laboratory-type processes could be reported, with efficiencies of 18.2 % on EFG ribbons and 14.4 % on RGS ribbons. The defect mechanism of these materials has been studied in detail and efficiency limits have been indicated. The paper will refer to the separate contributions submitted to the conference by the different partners on specific topics.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1151-1157, Market demand for a lower price per Wattpeak asks for the development of solar cell designs with low production costs and high performance. One approach to reach high efficiency with a solar cell structure containing a diffused emitter on a p-type silicon wafer is to implement a PERC structure on the rear [1]. This structure becomes advantageous to the standard screen printed solar cell when its production cost stays comparable to the latter’s and offers higher efficiency [2]. Since this technique can inherently be applied to thinner wafers, reduced material consumption offers an additional advantage. The purpose of this work is to analyse the solar cells resulting from a production sequence able to create a PERC structure on thin silicon wafers using steps available in the PV industry or at least close to industrial application and estimate further sound improvements. This approach, at its current state of the art, achieves on Czochralski (Cz) wafers of 120 μm thickness a stable efficiency of 18.0 %.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 958-962, CrystalClear is a large integrated project funded by the European Commission that aims to drastically reduce the cost of crystalline Si PV modules, down to 1 Euro/Wp. Among the different subprojects, the one dealing with the development of advanced solar cells is relatively large (with 11 partners out of the 15 Crystal Clear partners taking part) and has a crucial role. The goal of the subproject is to develop cell design concepts and manufacturing processes that would enable a reduction in the order of 40% of the cell processing costs per Wp. In this paper, we give an overview of all the development work that has taken place in the CrystalClear solar cells subproject so far. World class results have been achieved, particularly on high efficiency cells on Si ribbons, and on industrial-type solar cells on very thin (120 μm thick) substrates.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1459-1461, This work shows continuing progress in screen-printing of crystalline solar cells front metallization as a well-proven technology compared to technically relatively new processes such as ink-jet or aerosol printing. A combined optimisation of screens and silver metallisation pastes demonstrates the feasibility of a direct production of fine-line metallisation contacts with high aspect ratio of the fired fingers using screen emulsion openings of 55 μm. Additionally, suitability for subsequent galvanic reinforcement of the PV-cell front contact is demonstrated. Using the newly developed screen and paste materials mono-crystalline Si solar cells with an average efficiency of more than 17.5% in a single print-firing process could be manufactured. Subsequent galvanic reinforcement yielded average efficiencies of more than 17.6%.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1704-1707, Large-area (125x125 mm2) solar cells using standard CZ material and a close-to-industry front structure including a diffused POCl3 emitter, a SiNx:H anti-reflection coating and screen-printed contacts which were fine-line printed and thickened by light-induced silver plating were manufactured applying a dielectrically passivated and locally contacted rear structure. The rear passivation was achieved by a PECVD stack of SiOxNy:H and SiNx:H. The rear Al layer on top of the dielectric was screen-printed and co-fired with the front contacts. The local rear contacts were subsequently prepared by laser-firing. The best dielectrically passivated LFC (Al-BSF reference) cell showed VOC=622 mV (614 mV), JSC=36.2 mA/cm2 (35.6 mA/cm2), FF=78 % (79 %) which ends up in an energy conversion efficiency of 17.5 % (17.4 %). The passivated LFC cell clearly outperforms the Al-BSF reference when looking at IQE data. Light microscope images and surface topography measurements of the front contacts are presented.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1527-1529, Bifacial silicon solar cells with silicon nitride passivation are investigated with respect to the influence of the used base resistivity of the Czochralski silicon. In this paper will be shown that no effective back surface field is formed in a firing through approach and that this will limit the open circuit voltage. The open circuit voltage of these solar cells is determined by the built-in potential between the emitter and the base. The passivation quality of the silicon nitride on the rear side is superior to the aluminum back surface field, so that a gain in short circuit current can be observed for the lower base resistivity of the silicon and a maintaining of the short circuit current for the high base resistivity investigated here. Additionally the benefits of bifacial solar cell design are simulated with PC1D.