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29th European Photovoltaic Solar Energy Conference and Exhibition; 834-837, We demonstrate a numerically optimized double layer antireflective coating (DLARC) composed of dielectric materials, the application of which led to the imec best IBC solar cell of 23.4 [%]. Synthesis, optimization procedures and technological aspects were investigated in the context of application of the DLARC to the existing IBC cell architecture at imec. The numerical simulation results are demonstrated on both planar and textured surfaces. Good agreement with experimental data is obtained. Subsequently, the influence of deposition error posed by industrial PECVD deposition on the spectral characteristics of the front reflectance is investigated numerically, and confirmed experimentally. The constraints for stable, repetitive deposition of such multilayer coating are extracted. Finally, the design was tested on the cell level yielding 0.26 [%] average, absolute efficiency gain. The cell were 4 [cm2] in size, manufactured on Czochralski-grown silicon.

28th European Photovoltaic Solar Energy Conference and Exhibition; 757-760, This work reports on the feasibility to implement a cost effective dry oxidation step in a Passivated Emitter and Rear Cell (PERC) structure on p-type Cz Silicon substrates. PERC solar cells have been extensively investigated in the recent years for industrial implementation. One of the main challenges is to combine the integration of cost effective process steps while maintaining high cell efficiency. In our previous work, we introduced at imec the use of a thermal oxide below the front ARC and below the rear dielectric PECVD SiOx/SiNx stack for enhanced surface passivation. In this study, we demonstrate that a low thermal budget of 800oC coupled with a drastic reduction of oxidation time down to 15 min is sufficient for the growth of a high quality thermal oxide without adversely affecting the emitter properties. We show that the level of Dit at the silicon interface after oxidation is not determinant for the level of surface passivation but rather the hydrogenation provided by the SiNx after firing. We also show that the resulting SIMS emitter Phosphorous profiles after the low temperature oxidation maintain a surface concentration above 1×1020/cm3, which is fully compatible with screen printing technology. Assisted by the latest developments on commercial silver paste, this enables to contact homogeneous emitters up to 90 Ω/ with measured FF above 79% on the cell level after firing optimisation. All devices were fabricated on substrates area of 156 mm × 156 mm with a base resistivity of 2 Ohm.cm and a thickness of 170 μm. The PERC cells have front Ag screen printed contacts with a 3- busbar pattern, a thin thermal oxide on both sides with a rear PECVD SiOx/SiNx stack. Average conversion efficiency above 19.7% are achieved on such large area substrates. Several optimisation cycles have led to best cell efficiency of 20.1%.

27th European Photovoltaic Solar Energy Conference and Exhibition; 1602-1606, An industrially applicable process flow for the formation of rear side passivated solar cells has been suggested by IMEC in 2005. Since then considerable improvements in solar cell efficiencies have been obtained with that type of process. In parallel simplifications and cost reductions were needed to bring it to production. IMEC’s Industrial Affiliate Programme (IIAP) offers industrial partners the possibility to actively join development efforts with IMEC and other partners sending residents to work at IMEC as part of a research team. Selected development results of this IIAP are presented here. On large area homogeneous emitter CZ-Si solar cells FhG-SE Cal-Lab confirmed solar cell efficiencies of 20.0 and 20.3% for screen printed Ag and reliable plated Cu front contacts, respectively. Fill factors of 80% have been achieved for fully screen printed (front and rear) solar cells with low cost rear side dielectric stack layers. Cu plated contacts show reliable module data in IEC test conditions. Latest results with average solar cell efficiencies of 20.4% over the length of a CZ-Si ingot with top efficiencies of 20.6% are just an intermediate step. IMEC sees a road to >21% efficient i-PERL solar cells in production.