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33rd European Photovoltaic Solar Energy Conference and Exhibition; 641-645, This paper reports on the analysis of the photovoltaic (PV) potential of PERC structures and focuses on the carrier recombination and series resistance related losses caused by the back-side Al-Si local contacts. More precisely, we propose a 3-steps procedure to define a process window for the back-side LCO (Laser Contact Opening) design of a PERC solar cell. This method takes into account the 3 main PV performance limitations coming from the LCO design: void occurrence limitation, lateral resistance limitation and carrier recombination limitation. The proposed procedure starts with a simplified determination of the substrate main bulk properties followed by an evaluation of surfaces recombination parameters via symmetrical and asymmetrical passivated structures based on high quality p-type Cz wafers. Then, the void occurrence is addressed with a specific approach combining variations of the opening width and changes in the firing temperature, supported by LBIC (Light Beam Induced Current) analyses (for voids density calculation) and illuminated IV measurements. Eventually, an experimental matrix modulates the LCO fraction (for an opening width and firing conditions limiting void occurrence) in order to define the good trade-off between low lateral resistances and reduced carrier recombination at the Al-BSF/Si interface. By applying these optimization procedures, PERC cells with Voc above 665 mV were fabricated with performances essentially limited by front-surface and bulk recombinations.

28th European Photovoltaic Solar Energy Conference and Exhibition; 1831-1834, A new method to obtain antireflection and passivation coatings of silicon solar cells is presented. In this method hydrogenated silicon nitride (SiNx:H) films are obtained by atmospheric pressure plasma-enhanced chemical vapor deposition (AP-PECVD). This process could entail an augmentation of the throughput and yield of the silicon solar cell processing and thus reduce the cost of photovoltaic systems. The chemical composition and optical properties of the AP-PECVD SiNx:H films are determined. The passivation behavior of the SiNx:H films is also characterized. To evaluate the interest of these films for the photovoltaic industry, solar cells coated with AP-PECVD SiNx:H films are obtained and compared with reference cells.

27th European Photovoltaic Solar Energy Conference and Exhibition; 3445-3448, Colored photovoltaic (PV) modules have been manufactured with monolayer interferential filters integrated directly onto bulk Si PV cells or on large surface glass covers. Whatever the color, the filters’ conception is such that the relative short circuit current loss is designed and experimentally verified to be less than 15%. Somehow the higher series resistance of the purple PV cells with the thickest SiN layer on Si induces an important fill factor loss. The best conversion yield is obtained with the PV cells grey color for which the relative power loss is only 8 %. Coloring the glass cover is the best way to obtain conversion yield losses which are limited by the theoretical current losses. Colors can be brought to PV modules at a production cost that is equivalent to the standard blue modules.

27th European Photovoltaic Solar Energy Conference and Exhibition; 1921-1925, The excessive reflectivity from mc-Si solar cells is a limitation to obtain high efficiencies. Wet acidic or alkaline chemical texture processes are usually used in photovoltaic industry to reduce the surface reflectivity. However, they suffer from lowering just a few the surface reflectivity. Nano-imprint technology combined with plasma etching offer a better optical potential with the advantage to allow defined geometry silicon surface patterning independently of the crystalline orientation. The stamp needed for Nano Imprint technology is defined from anisotropic wet chemical etching on mono-crystalline silicon, which is the high efficiency texture used for a silicon substrate. This stamp is then printed in a resin beforehand deposited on the mc-Si surface. The transfer of the inverted pyramid shape in the mc-Si is provided by plasma etching, in such conditions that the pyramidal profile in the mc-Si has an amplified aspect ratio compared to the stamp. An absolute efficiency gain of 0.3 % was demonstrated on 100 mm x 100 mm mc-Si solar cells (16.5 % on reference alkaline mc-Si texturised cells compared to 16.8 % on “imprint” mc-Si textured cells). These results are promising, but still below those expected in terms of efficiency due to losses in Voc. The objective is to obtain an absolute efficiency gain of 1%, which could be obtained if the reflectivity gain is completely transformed in efficiency gain.

27th European Photovoltaic Solar Energy Conference and Exhibition; 1489-1493, In this paper the high potential of solar cells with homogeneous implanted emitters and screen printed metallization is assessed on p-type wafers 239 cm2. A 0.8% absolute gain efficiency is achieved compared to a standard solar cell including a phosphorus diffused emitter, leading the efficiency up to 19.2%. In order to improve the solar cell efficiency, focus is placed on well known advanced PERC solar cell architecture with optimized back side passivation. The approach is to combine the surface passivation provided by a thin oxide layer grown during the post-implantation annealing process with a deposited capping silicon nitridre layer. This paper presents the influence of the silicon nitride layer content on passivation and optical properties of solar cells. Laser ablation is also studied and conditions are found to properly remove the dielectric layers without inducing silicon surface damages. Based on this development, implanted emitter and local Al-BSF with SiO2/SiNx back passivation are integrated in solar cells reaching 19.4% efficiency. The presence of a detrimental parasitic shunting effect finally highlights the importance of developing dielectric layers less positively charged to lead the way on achieving 20% efficiency.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 1845-1848, Our work compares laser ablation processes of silicon nitride material deposited onto pre-diffused silicon substrate by using a nanosecond, 248nm Excimer source and a picosecond, 355nm UV source. It is shown that effective removal of SiNx could be obtained but energy has to be carefully chosen to limit modifications of the underlying silicon. Physical mechanisms involved during each process are discussed and compared with literature.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 1852-1854, Our work focuses on industrial laser doping process from phosphosilicate glass with a high energy, large spot, pulsed UV (308nm) Excimer laser source to realize selective emitter structures. A highly homogenous process enabling the accurate control of two different N-doped emitters by the simultaneous activation of low and highly doped areas is demonstrated. At present, solar cells performances are limited actually by both Jsc and FF. Current losses will be avoided by adapting the laser beam to irradiate on front contact regions only while optimized screen printing process should solve contact resistance issue.

24th European Photovoltaic Solar Energy Conference, 21-25 September 2009, Hamburg, Germany; 1660-1664, This work is a comparative study of the optical and chemical properties of Hydrogenated Silicon Nitride films (SiNx:Hy) made with an atmospheric pressure PECVD (AP - Plasma Enhanced Chemical Vapor Deposition) process under development and an industrial Low Pressure (LP) PECVD reactor. The AP-PECVD films are deposited with a laboratory scale reactor using Ar, SiH4 and NH3 gas mixtures whereas the LP-PECVD silicon nitride is obtained in a Centrotherm reactor with NH3 and SiH4 as reactive gases. The optical parameters (refractive index and extinction coefficient) of the two silicon nitrides are compared before and after Rapid Thermal Annealing (RTA) by means of ellipsometric measurements and New Amorphous dispersion law. To compare the different chemistries of the layers, FTIR measurements are done, also before and after RTA. Si-H and N-H absorption peaks are related to the refractive index showing that the same optical properties are obtained with different chemical compositions. To finalize the comparison between LP and AP-PECVD, coatings have been processed on multicrystalline silicon solar cells.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1581-1585, This work is the first step of a study of antireflecting and passivating properties of Hydrogenated Silicon Nitride films (SiNx:Hy) made with a new atmospheric pressure PECVD process. Photovoltaic properties are correlated with physico-chemical ones. Films are deposited with a laboratory scale system of Atmospheric Pressure Plasma Enhanced Chemical Vapor Deposition (AP-PECVD) using Ar, SiH4 and NH3 gas mixtures. According to experimental parameters such as the ammonia to silane ratio and the substrate temperature, the surface passivation is determined on FZ silicon wafer by photoconductance decay measurements. The evolution during the days following the deposit realization is also studied. The refractive index and the extinction coefficient are determined from ellipsometry measurements. The chemical composition of the SiNx:Hy is studied by Fourier Transformed InfraRed spectroscopy (FTIR), Secondary Ion Mass Spectroscopy (SIMS), X-ray Photoelectron Spectroscopy (XPS), and Elastic Recoil Detection Analysis (ERDA). Scanning Electron Microscopy (SEM) photographs coupled to the other diagnostics gives informations on the layer morphology. SiNx:Hy films deposited at atmospheric pressure passivate the surface of silicon wafers even if there is presence of porosity, dense layers are achieved for deposit temperatures above 330°C with a good chemical and morphological homogeneity.

23rd European Photovoltaic Solar Energy Conference and Exhibition, 1-5 September 2008, Valencia, Spain; 1733-1736, The formation of selective emitters is a key issue to achieve higher efficiencies on industrial screen printed silicon solar cells. A study on the development of selective emitter concepts is presented using POCl3 diffusion for the development of the high and low doped emitters. The work is focused on the application of the developed technology to an industrial level, considering the alignment requirements between the highly doped emitter pattern and the front silver grid. Our selective emitter process shows a great efficiency improvement of 0.5% absolute which is related to an improved spectral response in the short wavelength range. Efficiencies of 16.6% are obtained on 150 mm x 150 mm mc-Si cells and 17.8% on 125 mm x 125 mm c-Si cells.