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32nd European Photovoltaic Solar Energy Conference and Exhibition; 811-815, The process of annealing a SiO2 dielectric layer coated in aluminium, termed the alneal, is known to produce some of the most effective surface passivation for silicon. However, it is traditionally performed on a SiO2 dielectric coating which has sub-optimal anti-reflection properties. In this work it is shown that it is possible to achieve alneal passivation through a double layer SiO2/TiO2 stack. TiO2 was investigated as it is one of the most effective antireflection coatings available and its deposition technology is advanced and cost effective. Here, the alneal was carried out on n-type ~40 Ωcm Cz-Si coated with a SiO2/TiO2 dielectric stack. In the best case, the alneal produced a lifetime increase from ~15 μs to 3084 μs, which equates to a SRV ≤ 10 cm/s or a J0e of 32 fA/cm2. This increase in lifetime was comparable to that achieved by a conventional alneal on a single layer SiO2 specimen. It was also found that the thicker the TiO2, the less effective the alneal was at passivating. Lastly, the passivation achieved after the alneal on the SiO2/TiO2 bilayer was found to be more stable than that achieved on the conventional single SiO2 layer.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 707-710, Surface recombination remains a major factor limiting the efficiency of silicon solar cells. The postprocessing of dielectric films used as surface coatings has been previously demonstrated an effective technique to improve their passivation quality. In this paper extrinsic methods are demonstrated to produce the lowest reported surface recombination velocity in solar relevant n-type silicon. Recombination velocities below 2.8 cm/s at an injection of 1015 cm-3, are achieved using extrinsic field-effect passivation, or < 0.6 cm/s when using combined extrinsic chemical and extrinsic field effect passivation. These are equivalent to emitter saturation current densities J0e

32nd European Photovoltaic Solar Energy Conference and Exhibition; 328-330, In imec’s i2-module concept, silicon heterojunction interdigitated back-contacted (SHJ-IBC) solar cells are fabricated on monocrystalline foils bonded to glass. The proposed technology allows for cell processing on thin wafers mechanically supported by the glass, increasing the yield of processing such thin wafers. A process sequence for SHJ-IBC cell fabrication that can be applied to bonded thin foils is described. We investigated and optimized individual process steps on thick wafers. Then the developed steps were integrated into a process flow to fabricate solar cells on wafers with different thicknesses and bonding agents. On wafers with a thickness of 190 μm, functional cells with efficiencies of 22.6% and 21.7% were made on freestanding and silicone bonded wafers, respectively. On thin wafers of 57 μm, our best SHJ-IBC cell on an EVA bonded wafer exhibits excellent Voc of 740 mV and efficiency of 20.0%, which demonstrates the high potential of the i2-module concept.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 407-412, We present bifacial fully ion implanted and screen-printed n-PERT cells, fabricated either by applying a single co-anneal process to cure the implant damage or by applying two separate anneals after boron/BF2 and phosphorous implant, respectively. In the first case of boron implant and co-anneal our best cells achieve an independently measured front (rear) side efficiency of 21.0 % (20.43 %) and for the boron implant and separate anneal the efficiency is 21.5 % (21.31 %). To the best of our knowledge these values are the highest efficiencies reported so far for fully ion implanted and screen-printed bifacial n-PERT cells. We furthermore show that light treatment of boron-implanted and co-annealed n-PERT cells increases the cell efficiency by 0.6 %abs. This diminish the efficiency gap to separately annealed cells. We measure a bifacial factor of 99.4 % that is the highest value reported so far for any high-efficiency Si cell. The high bifaciality enables an adapted module interconnection scheme called here Flip-Flop, which is based on a front-to-front and rear-to-rear interconnection of cells with alternating orientation (n+ or p+ side facing up). Based on the measured IV-characteristic of a cell with a bifacial factor of 97 % (“conservative scenario”) we demonstrate that the Flip-Flop interconnection scheme has the potential for a module efficiency improvement of 0.5 %abs on aperture area (as compared to the conventional “all cells emitter up” configuration) despite the 3 % current mismatch. We experimentally demonstrate a monofacial 16-cell Flip-Flop module that achieves an aperture area efficiency of 20.5 %.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 651-655, In a-Si:H/c-Si heterojunction solar cells the UV absorption of amorphous layers limits the current generation. The use of a more transparent material like a-SiOx:H films is a key to further enhance the efficiency of this kind of cells. At the same time this layer must guarantee high surface passivation of the c-Si wafer to be suitable in high efficiency solar cell manufacturing. As for amorphous silicon, thermal annealing procedures are considered as valuable steps to enhance and stabilize thin film properties, when performed at opportune temperature. In order to avoid damages of the amorphous layer, each cell fabrication step should be carried at temperature lower than the emitter formation one. However, when thermal annealing is applied as one of the early fabrication step, the temperature can be high enough to obtain the best passivation properties. In this work we have analyzed the effect of several thermal treatments different for temperature, duration and surrounding atmosphere on a-SiOx:H/c-Si/a-SiOx:H structure. We have fully characterized the samples with the aid of effective lifetime evaluation and FTIR spectra to correlate the effect of thermal annealing to the a-SiOx:H/c-Si interface.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 703-706, In this work, we present n-type bifacial solar cells with a BBr3 thermally diffused emitter on the front side. Our study related mainly to the boron profiles of the front-side emitter. We optimized the front-side boron emitter by removing the boron-depleted region by means of a spin-etching technique. The boron profiles of non-etched and etched samples were examined. Passivation qualities were also studied on non-etched and etched symmetrical p+/n/p+ samples. A reduction in the emitter saturation current density J0e in the sample in which the depletion region had been etched was investigated. A high cell efficiency of 19.6% was achieved by removing the depleted region on the front side.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 456-459, First Solar has launched mass production of high-efficiency crystalline silicon solar cells. The manufacturing sequence employs a new technology that eliminates recombination at the metal contacts. This “shielding” of the contacts allows a new degree of freedom for the metal grid design, i.e. the optimization is only a trade-off between shading and resistive losses. Contact recombination is so low that it doesn’t need to be factored in anymore. In combination with a fine line copper metallization process sequence, median efficiencies over 21% are achieved on a 100 MWp pilot line. 72-cell PV modules with standard soldering and interconnection technology have power bins (-0 to +5W) of 360 to 370 Wp.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 317-322, We investigate the impact of high-temperature processes on phosphorus-doped n-type Czochralski-grown silicon (Cz-Si) wafers. Wafers from five ingots are subjected to high-temperature process sequences with different temperatures, times, and gas atmospheres. The process sequences are specifically chosen to represent different routes for the fabrication of high-efficiency n-type Cz-Si solar cells. As POCl3 diffusion is known for its effective gettering of metal impurities, it is preferably used as the last high-temperature step. However, our results show that other process sequences, e.g. with BBr3 diffusion as last high-temperature step, enable high charge carrier lifetimes in the range of a few milliseconds as well. For some materials and process sequences, ring-shaped defect structures are observed while for others increased charge carrier lifetimes by a factor up to 2.6 are found compared to their initial values prior to high temperature processing.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 951-954, In this paper, we present n-type rear junction (RJ) PERT (Passivated Emitter Rear Totally-diffused) solar cell with the process improvement of Laser Contact Opening (LCO) process and rear pattern opened by laser. In detail, effect of laser process parameter such as laser power and pulse duration was evaluated in terms of impact on the cell efficiency and opening shape. Also LCO pattern such as line, dash and dot was optimized to reduce rear electrode contact area to minimize the recombination characteristics of n-RJ-PERT cells. Through this, we achieved 21.77% efficiency, and 686 mV open-circuit voltage(in-house measured) of n-RJ-PERT solar cell with plated Ni/Ag front contacts, Al2O3 rear passivation, and screen-printed local Al emitter on 110μm-thickness 6-inch n-type Czochralski (Cz) single crystalline.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 892-895, The series and shunt resistance values play an influential role in the output of a photovoltaic device. Additionally, they may also be useful parameters to assess the cell or module quality. Calculation of these values however is non-trivial, consequently a number of experimental and non-experimental techniques currently exist in order to estimate their values. In previous work [1], a method was proposed to calculate the values of series and shunt resistances at maximum power primarily using the experimental data typically published by the manufacturer. This numerical method based on the multi-dimensional Newton-Raphson method and current voltage equations expressed using the Lambert W-function is however computationally burdensome and therefore unsuitable for implementation in an environment where speed is needed such as manufacturing or field testing. Here we present a rapid method of calculation based on a feed forward type multi-layer perceptron artificial neural network (ANN). Current-voltage data were experimentally acquired for a single multi-crystalline silicon cell under varying levels of outdoor illumination from which the short circuit current, open circuit voltage, and location of the maximum power point values were obtained as typically published by the manufacturer, forming the training set for the ANN. The corresponding values of series and shunt resistances were then calculated using the method of Ghani and Duke [1] to form the network target set. It was found in this study that the network could be successfully trained for this application providing a method to rapidly calculate these loss values. It may therefore be a beneficial quality assessment tool for photovoltaic device manufacturers, installers, and users.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 550-554, Co-development of silver printing pastes, screens with finer meshes, and advanced printing machines, enabled for a steady shrinkage of finger widths. Advancement on glass frits allowed for contacting of lower doped emitters, improving the cell parameters from the better passivation and low Auger recombinations of these advanced emitters. We evaluate in this paper, what the optimum finger line width would be, for cells having high number of busbars and advanced emitters. A grid optimization study is performed on standard reference p-type PERC using GRIDDLER software, varying finger line widths and aspect ratio for the different number of busbars. An optimum finger width is obtained for a given number of busbar and finger aspect ratio, beyond which further smaller finger line widths, the cell efficiency drops due to the large number of fingers required which results in increased optical shading and voltage losses. With advance emitters (high sheet resistance) similar observations are made. In other words, it is advantageous to have fine finger line widths for cells with high number of busbars and advanced emitters. Further, we show using the patented novel Pattern transfer technology (PTPTM) very small finger line widths with good aspect ratio can be achieved. PTPTM is a non-contact printing technology based on laser transfer hence has the potential to overcome the limitations of screen printing technology and increase cell performance in the future.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 565-570, In this work, we investigate boron-doped back surface field (BSF) formation from borosilicate glass (BSG) deposited by atmospheric pressure chemical vapor deposition (APCVD). Carrier lifetime samples with different boron concentration in the BSG are exposed to high-temperature processes with varying temperature and gas atmospheres. The development aims at producing p-type Si-based passivated emitter and rear totally diffused (PERT) cells in a POCl3 co-diffusion process. Our experiments confirm the critical impact of the O2 concentration on boron diffusion from APCVD BSG layers. For different peak temperatures Si surface oxidation formation need to be balanced carefully. Moderate diffusion temperatures of 875°C (30 min) yield a BSF doping with Rsh = 131 Ω/sq and a recombination current density of J0,BSF = 21 fA/cm² (planar surface, AlOx/SiNx-passivation). Finally, 156 mm sized PERT cells fabricated from p-type Czochralski-grown Si wafers using the developed co-diffusion process show peak efficiencies of 20.6%, confirming the feasibility of our co-diffusion approach.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 571-574, The results of pilot production of Interdigitated Back Contact (IBC) solar cells at Trina Solar with a low-cost industrial process are presented. The 6” IBC pilot line was established in 2015 and continuous improvements were implemented over one year. In recent batches, the median cell efficiency has reached 23.0%, and the best cell efficiency was 23.2%. Advanced IBC cells with finer geometries and smaller contacts reached an efficiency of 23.5%. Further cell efficiency improvements and cost reduction are under development.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 487-494, Different injection levels make the comparison of BO Regeneration kinetics in different Si wafers or solar cells difficult, e.g., when samples made of different materials featuring different background lifetime levels are to be compared. A correction factor is presented that is able to compensate for these differences in injection level during Regeneration. This is used to investigate the influence of metallic impurities, interstitial oxygen and different dopants on BO Regeneration kinetics. It is found that a POCl3 gettering step only affects Regeneration if the overall H concentration within the wafer is low. Interstitial oxygen is found to be less detrimental to Regeneration than assumed previously. The influence of different dopants is shown in a process leading to a stable regenerated lifetime, and the measured Regeneration rates can be compared because of the applied injection correction. A numerical fit optimization method is presented to separate the influence of the different dopants. It is shown that net doping concentration p0 is not relevant for BO Regeneration whereas B as well as Ga slow down the Regeneration process. An explanation within the H-model of BO Regeneration is given.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 625-627, In this work, a front-side metallization based on laser ablation and electrochemical plating contacts is proposed for the improvement in shading loss and short-circuit current density. The influences of nanosecond laser ablation on finger width, surface morphology, and cell performance are investigated. The optimization of laser ablation and electroplating contacts are achieved to improve the finger width, aspect ratio, and metal shading effect. The results of Suns-Voc measurement indicate the improvement in recombination issues. A average performance of Ni/Cu plated solar cell exhibits a 0.54 mA/cm2 increase of short-circuit current density (Jsc), 0.10% increase of fill factor (FF), 0.03 Ωcm2 decrease of series resistance (Rs), and 0.28% increase of conversion efficiency (n).

32nd European Photovoltaic Solar Energy Conference and Exhibition; 738-741, The interface passivation quality of a-Si/c-Si plays the decisive role in attaining high open circuit voltage of Si heterojunction solar cells. The passivation quality of this interface can be improved by using Hydrogen plasma treatments, which helps to saturate the dangling bonds by Hydrogen termination. In this work, different plasma treatment methodologies like Pre, Post and Intermediate Hydrogen plasma treatments during the deposition of a-Si are investigated and their effect on passivation quality was studied using minority carrier lifetime measurements and Fourier Transform Infrared Spectroscopy (FTIR). The Hydrogen Plasma treatments were done using rf- PECVD at 80% Hydrogen dilution and at a low substrate temperature of 200 °C. The treatments were done for 30 seconds at a low power density of 30mW/cm2 to avoid the plasma damage. The improved passivation quality due to hydrogen plasma treatment results in surface recombination velocity as low as ~ 24 cm/s with an implied VOC of 700 mV.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 580-582, This contribution presents our latest progress on 5x5 inch solar cells yielding a maximum efficiency = 22.0%. The cell process utilizes four laser irradiation steps for emitter and back surface doping as well as for the ablation of the rear passivation layer and structuring of the metallization. The improvement from the previously measured = 20.8% is achieved by busbar-tapering, improved cleaning and higher area utilization. Photolumines-cence proves the homogeneity and accuracy of all four laser processes. Electroluminescence illustrates the improve-ment achieved by the tapered of the busbars and suggests that even higher efficiencies will be possible.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 786-790, Different busbar concepts with three, four, five and six busbars (BB) on standard silicon solar cells on both full cell format (156 mm x 156 mm) and half-cell format (156 mm x 78 mm) were investigated. 40 prepared single-cell mini module specimens, five of each per variation, were tested with a flash cell tester to determine series resistance and maximum power for a relative comparison. Simulations with original measured parameters were compared to the determined values of the experiment. A dependency was found between the number of busbars and the finger grid design, all together affecting series resistance and efficiency. An optimized busbar concept with at least 4-BB technology is recommended as a first step due to performance improvement and economic issues.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 915-921, Standardizing illuminated IV measurements of bifacial solar cells and modules is a central objective for the introduction of bifacial products into the market. In this paper, the application of monofacial IV measurement conditions to bifacial solar cells is evaluated in an inter-laboratory comparison among seven research institutes in Europe. Bifacial silicon solar cells manufactured at five different sites with five different fabrication technologies were used in this investigation. We demonstrate that several characteristics of the measurement setups which are of minor importance for the measurement of monofacial solar cells can significantly affect bifacial solar cell measurements: (i) the reflectance of the measurement chuck and (ii) the electrical conductance of the chuck implying specific contacting schemes. When dividing the measurement results of this round robin into two groups according to chuck reflectance and conductance, the deviations in the IV parameters among the different partners are mostly within the uncertainty limits commonly reported for monofacial solar cell measurements. For standardization of bifacial solar cell measurements, it is therefore important to define admissible ranges for the chuck reflectance and to specify the contacting scheme in the standard.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 808-810, In the development of high efficiency crystalline Si solar cells, decreasing bulk and surface recombination velocities of the minority carriers is vital. As the bulk recombination could be suppressed by enhancing the material quality, the effect of surface recombination on cell performance becomes more dominant. Also, recent studies have revealed that the area under the metal contacted region needs to be passivated to minimize the carrier recombination. The passivation of front and back surface of the cell can be achieved using different techniques and materials. Dry oxidation is a well-known process by the industry and requires high temperature treatment that increases thermal budget of the whole fabrication sequence and also degrades bulk lifetime. For this reason, a low temperature technique like wet chemical oxidation is highly desirable for the growth of thin oxide layers. In this work, 4 different wet chemical oxidation techniques based on nitric acid (HNO3), hydrogen peroxide (H2O2), RCA II (HCl: H2O2) and hydrochloric acid (HCl) solutions were studied and corresponding cell performances was compared with that of dry oxidation.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 943-945, In this work, the evaluation results on industrial p-type mc-Si PERC cells using spatial atomic layer deposition for aluminum oxide from SoLayTec are shown. By optimizing the process flow and integrating a postdeposition anneal into the SiNx capping process we achieve 0.15% higher cell efficiency compared to remote microwave plasma-enhanced chemical vapor deposition. Furthermore, it is shown that the improved passivation quality resulting in Voc gain remains constant during light and elevated temperature induced degradation measurements.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 285-288, This paper aims at presenting the CRYSTALMAX technology developed from the collaboration of ECM Green Tech crystallization furnace manufacturer with CEA-INES research institute. CRYSTALMAX technology provides fully oriented 650 kg silicon ingots, obtained by seed-assisted cast solidification. Resulting 6inch full square wafers feature low production costs that could be further reduced by reduced kerf loss offered by diamond wire sawing, the recycling of Cz-seeds, or the use of SoGM feedstock. P-type CRYSTALMAX wafers were processed as conventional Al-BSF solar cells. The variation of the cells performances along the ingot’s height are detailed. Correlations between wafer impurity (Oi; Cs) content, cell performances, effective carrier diffusion length are presented. Device stability towards prolonged light exposure is also evaluated.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 753-755, This work gives an overview about the current status and the ongoing development of the silicon heterojunction (SHJ) solar cell process at HZB. Our research work focuses on the development of highly transparent nanocrystalline front surface field (FSF) layers and innovative transparent conductive oxide (TCO) layers as front electrodes for rear emitter SHJ solar cells. By introducing water vapor into the front ITO sputtering process we show an increase of 0.4 % absolute in conversion efficiency compared with our standard ITO process without water vapor. Furthermore first results for a rear emitter cell structure are presented with a conversion efficiency exceeding 21% for 4 cm² SHJ solar cells on n-type CZ-Si. Introducing further process optimizations, we expect to achieve conversion efficiencies above 22% for our baseline process sequence in the near future.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 946-950, In this paper, we report the results of an upgrade from an Al-BSF solar cell line to a PERC (passivated emitter and rear cell) solar cell line, based on p-type mono-crystalline silicon (mono c-Si) material. For the rear side Al2O3 passivation, an InPassion ALD system of SoLayTec was used. The PERC solar cell optimization has been done in three main steps: first we optimized the rear side SiNx capping layer, leading to a solar cell efficiency increase of +0.4%abs with respect to the mono c-Si Al-BSF solar cell baseline. Secondly, we optimized the rear side polishing depth from 1-2 μm to 3-4 μm, which results in a solar cell efficiency gain of +0.5%abs with respect to the standard Al-BSF solar cell baseline. For the third optimization, the emitter sheet resistance has been increased from (78±3) Ω/sq to (90±5) Ω/sq, resulting in a solar cell efficiency of (20.44±0.17)% and a gain of >+0.8%abs with respect to the Al-BSF baseline. After several repeat runs, where the number of PERC solar cells has been increased to >1000 wafers per run with >1.0%abs solar cell efficiency gain, >50000 PERC solar cells have been processed over two days with a stable solar cell efficiency of (20.5±0.3)% and best cell with efficiency of 21.1%. The reliability of the InPassion ALD system has been improved by decreasing the breakage rate from 0.19%abs to 0.05%abs. Finally, it has been proven that with the latest configuration of the system, the breakage rate can be reduced even more to ≤0.05%abs.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1015-1017, In our previous works the possibility of growing silicon rods suitable for FZ process was shown, however, the use of the high-energy process such as electron beam melting (EBM) may lead to generation of impurities which substantially reduce the efficiency of solar cells. EBM grown rods were recrystallized with FZ. Due to FZ process purity all impurities are relied to EBM process and rod growth. FTIR was used to conrtol levels of impurities. Slight removal of phosphorus and the generation of boron and aluminium were noticed. The level of contamination is hundreds of ppta and is not crucial for the quality of the single crystals used in solar energy. The attempt to reliably examine the level of other impurities with GDMS analysis has failed due to insignificant quantities of impurities and the high resistance of the monitored sample. High lifetime at the end of the grown single crystal indirectly evidences of the absence of significant contaminations. Thus, single crystals obtained utilising the described technical processes are a promising material for the production of highly-efficient solar cells.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 715-717, Metal wrap through silicon heterojunction (MWT-SHJ) cells and modules combine the positive benefits of both underlying technologies: namely high Voc, higher Jsc and higher FF maintained before and after module encapsulation. We obtained 22.0% efficiency with low temperature Ag paste metallisation of front side and more than 23% on copper plated front metallisation. Voc values above 730 mV have been achieved, demonstrating that this architecture maintains the exceptional passivation of SHJ devices. The MWT cell and module structure offers even greater advantages when applied to SHJ solar cells: i) front side Ag consumption reduction up to a factor two; ii) low temperature cell interconnection concurrently with the encapsulation. Our record MWT-SHJ solar cells and modules are manufactured using industrially proven tools. The metallisation choice gives ample room to manufacturers to optimise based on internal cost structure and business strategy.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 300-306, During the production of silicon wafers with diamond wire the wire is moved regularly back and forth with a small fresh wire supply. As a consequence diamond wire is used very intensively and passes several times the wire web, contrary to the single pass during the slurry-based process with unidirectional wire movement. This results in a nonuniform wear and subsequently performance reduction of the diamond wire along the wire web that becomes visible in a complex wire bow behavior. Particularly designed diamond wire cuts and measurements of wire bow reveal that besides the uniformly increasing wire abrasion due to sawing of silicon, the wire is additionally damaged during the first contact with silicon, the winding on and off the wire spools and the sawing of beam material. It is shown that different diamond wires are more or less sensitive to damage during the first contact with silicon and that different beam materials result in more or less wire wear. At last, a cut without winding the wire on and off the wire spools suggests that a stable wire tension force has a major impact on diamond wire performance.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 383-390, This work reports on state-of-the-art silicon material characterization by calibrated photoluminescence imaging (PLI). PL imaging techniques allow for a characterization of a large variety of material properties, ranging from bulk and surface recombination properties of bare silicon ingots, to crystal structure, dopant concentration and bulk lifetime of silicon wafers up to material limiting impurities. In combination with solar cell simulations, injec-tion-dependent PLI of processed wafers provides a method for determining the material’s efficiency potential. In this contribution, we present two methods for imaging the concentration of interstitial iron at passivated silicon slices and at unpassivated silicon ingots. The latter is achieved by our latest progress in PL-based charge carrier bulk lifetime measurements with highest sensitivity, giving access to the bulk recombination properties of the ingot. Additionally, we present an improved analysis of specific loss mechanisms in silicon based on de-smeared injection-dependent life-time images of processed wafers, which is demonstrated on the example of the bulk-related efficiency limitations in high-performance multicrystalline silicon. This latest progress rounds off the established techniques, enhancing the potential of PL based imaging techniques for a comprehensive assessment of silicon material quality, from limitations in bare silicon ingots to efficiency loss mechanisms in processed samples.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 555-559, The theoretical long-term stability of modules with prior boron-oxygen defect passivation and the in-situ passivation of boron-oxygen defects in the field are investigated using typical meteorological year (TMY2) data for locations of Hamburg, Sydney, Tucson and Wuhan. Results show that a worst-case scenario of the long-term stability for ground-mounted systems installed in desert locations, destabilisation of the passivated boron-oxygen defects is of no concern within 40 years. It is also shown that roof-top photovoltaic systems with a 100 mm air gap and building integrated photovoltaic systems with no ventilation will be more prone to a potential destabilisation of the passivated defects rather than large centralised field arrays with ground-mounted systems due to the higher module operating temperatures. The modelling presented is supported by experimental data, with no de-stabilisation occurring for extended light-soaking (1000 hours at 70 °C or 400 hours at 160 °C). A best-case scenario is also shown for the potential of defect passivation in the field, showing a strong dependence on the location, mounting structure, and date of installation. In open circuit, a rapid passivation can occur within days for locations such as Sydney if installed in summer, whilst in cool climates, passivation can take several months.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 742-747, Objective of this work is to get softly doped and deep emitters in single thermal step. Due to high temperature diffusion, dead layer (electrically inactive) is formed which produces recombination centers and increases saturation current density (Joe). For appropriate choice of selective emitter in order to decrease emitter saturation current density (Joe), it is necessary to have a passivated emitters, i.e. with silicon nitride. We have presented a process which combines with standard technology used for selective emitter formation in a single thermal step which leads to lowly doped and deep emitters. This process is feasible for industrial fabrication of P/Al solar cells. In this process the gettering is higher than conventional process. Surface concentration value ranging from 3.6x1019 cm-3 to 7.2x1019 cm- 3 and depth junction values from 0.52 to 0.71 μm for sheet resistance ~100 Ω/ has obtained. The estimated saturation current density (Joe) could be around 30-40 fA/cm2 with optimization but in present work Joe is under 80 fA/cm2.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 677-679, Passivation paste for Passivated Emitter and Rear Cell (PERC) easily formed by screen-printing is described. The layer is composed of aluminum-other metal complex oxide. Passivation layer can be formed at low cost without gas-phase process. The forming procedure is as follows: (i) Printing the passivation paste on silicon wafers. (ii) Baking the wafers and volatilizing solvent. (iii) Annealing the wafers and promoting structure change to form passivation layer. The passivation layer is hard and stuck fast to the wafer. The carrier lifetimes of samples with the passivation layer are comparable to those of the ALD-AlOx applied sample. The negative fixed charge density of the paste is higher than -1×1012 cm-2. Quantum efficiency of the passivation paste applied PERC is equivalent to the ALD-AlOx applied reference cell.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 510-513, Terahertz emission from silicon wafers with silicon-oxide passivation lasers were measured using a laser terahertz emission microscope (LTEM) with strong correlation between THz waveform and the surface potential being observed. The surface potential were electrically tuned by an indium-tin oxide transparent electrode disk on the top and evaluated by capacitance-voltage (C-V) characteristics. The sample were excited by Ti-Sapphire laser pulses and the waveform of THz emission were measured by the THz time-domain spectroscopy techniques using LTEM. The observed waveform changed with the external bias and inverted near the flatband voltage, and changes similar to the C-V characteristics were shown in the peak amplitude. These results indicate that the LTEM can measure and map the surface band bending of Si by analysing the waveform of THz emission. We expect that the LTEM can be applied as an optical inspection tools of passivation layers of solar cells.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 363-366, In this paper, we report ENN’s results in R&D and mass production of high efficiency silicon heterojunction solar cells. Using large-size industrial equipment and mass production compatible processes, ENN has developed hybrid silicon technology (HST) and achieved 23.4% heterojunction solar cell efficiency. We have successfully developed a low-cost approach to mass production, i.e., converting existing Gen8.5 (5.7m2) thin film solar line to high efficiency HST fab by upgrading and modification of key equipment and line automation. We have achieved average cell efficiency of 21.6% in pilot production and demonstrated 317 Wp power output using standard 60-cell (156 mm) modules. ENN’s unique technology route to mass production of high efficiency heterojunction solar cells has comprehensive competition advantages such as low capital cost, high production capacity, proven equipment performance & reliability, and fast ramp-up, etc. This provides a viable path for more manufacturers to penetrate into this area, quickly commercialize low-cost heterojunction technology, and further increase its competitiveness.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 656-659, We present a new dopant-free back contact solar cells combined with the multi-functional emitter MoOx (20 nm)/Ag (15 nm)/MoOx (10 nm) (MAM) and 3nm Cs2CO3 as back surface field (BSF). The initial efficiency of 14.06% has been achieved, featuring the short circuit current density of 36.4 mA/cm2, open-circuit voltage of 591 mV and FF of 65.37% under STC (AM 1.5 global spectrum, 25 °C and 1000 W/m2) on the 4 cm2 area single side textured FZ n-Si. The front textured surface is passivated by plasma-enhanced chemical vapour deposition (PECVD) 70 nm SiNx and thermal oxide 10 nm SiO2. The rear-side 100 m interdigital gap, 250 m half-width electrode/Cs2CO3 and 750 m half-width electrode/MAM are deposited by thermal evaporation with accurate control by metal masking instead of high temperature diffusion and photolithographic masking. In order to achieve higher efficiency, we analyze the power loss, due to the front surface recombination velocity can be reduced to S=2.9 cm/s, the main losses of JSC are the light escape and back surface recombination. Additionally, the trend of series resistance changing with voltage is different from the homojunction back contact solar cells.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 831-834, In this paper, we present our study of fill factor (FF) loss mechanism for silicon heterojunction solar cells (SHJ) in relation to the quality of surface passivation. The effective minority carrier lifetime (eff) as a function of carrier injection density (n) has been modeled to identify the limiting factor of FF in our research. We have found that defects at a-Si:H/c-Si interface can cause low-quality surface passivation, which can be characterized by minority carrier lifetime at low-injection level, leading to reduction of fill factor. We propose a new mechanism that the presence of shallow defects with positive charges at the interface contributes to degradation of fill factor of SHJ cells. This hypothesis was verified using an AFORS-HET simulation tool in our study. Based on this study, we have developed an anti-contamination tray for wafer handling at the PECVD processing step. Our results show improvement of fill factor by an absolute value of 2%. SHJ solar cells with high efficiency of greater than 23% have been successfully fabricated using this technique.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1011-1014, Silicon is the dominant material in photovoltaic devices and with regard to the PV market growth, the demand for solar grade silicon feedstock is expected to be high in the future. Although solar silicon is currently produced through both chemical and metallurgical routes, the chemical route is still the main production method, which is expensive and have environmental challenges. Acid leaching of silicon, which is a metallurgical refining process is applied for silicon purification in the present research work. In this case, magnesium in different portions is added to liquid silicon containing B, P, Fe, Al, and other trace impurities. The Si-Mg melts are solidified under a controlled cooling rate and then they are treated by acid leaching through using dilute HCl solutions. The effect of magnesium concentration on the segregation and removal of the impurities, in particular P and B, is studied by electron microscopy and chemical analysis techniques. It is indicated that the process is effective for removing the impurities, and the purification is depending on the amount of Mg added into the silicon.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 983-986, The efficiency of all-back-contact (ABC), single-crystalline, silicon solar cells has increased steadily since Lammert and Schwartz introduced their novel interdigitated-back-contact design in 1975 [1]. This work explores the impact of high-temperature operation and absorption-layer thickness on performance by means of device simulations in Silvaco® AtlasTM. We begin by establishing a benchmark model that matches the experimentally derived parameters of a physical solar cell. Then, we alter the model to determine the optimum absorption-layer thickness as well as the cell’s performance at various temperatures. Finally, we combine both variables to simulate an optimally thin silicon ABC cell at elevated temperature in order to derive realistic performance characteristics for comparison.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 690-693, In this study, we report the deposition of Eu-doped (3wt%) phosphors on planar and textured Si solar cells via a silicate (SiO2) solution using spin-on film technique to enhance photovoltaic performance. The surface profile and dimensions of the phosphor particles were examined using electron scanning microscopy (SEM). Optical reflectance, photoluminescence (PL), and external quantum efficiency (EQE) were used to characterize the luminescent downshifting (LDS) of the Eu-doped silicate phosphor layer. Current density-voltage (J-V) curves under AM 1.5G simulation were used to confirm the contribution of LDS and the anti-reflectivity and shading produced by Eu-doped phosphors-particles of various dimensions. Experiment results revealed that larger phosphor particles have a more pronounced effect on the shading and reflectance of incident light. For planar solar cells, the short-circuit current density (Jsc) enhamcement by about 20% was obtained when deposited Eu-doped phosphors on the cells. On textured solar cells, however, the application of sub-micron Eu-doped phosphor particles increased the Jsc by 5.6%, far exceeding that of cells with larger Eu-doped phosphor particles (of 1.6%), compared to the reference cell.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 606-609, This paper is to study on a new doping technology, Cat-doping, in which phosphorus or boron atoms can be doped into crystalline-silicon (c-Si) at temperatures as low as 80 oC by utilizing catalytically cracked species of phosphine or diborane. This paper is also to study on its application to improvement of quality of silicon-nitride (SiNx) single passivation on c-Si, which is prepared by plasma-damage-less deposition method, catalytic chemical vapor deposition (Cat-CVD), often called Hot-Wire CVD. It is found that carrier lifetimes over 6 ms can be obtained by this SiNx single passivation when c-Si surface is Cat-doped in advance, and the Cat-CVD SiNx films exhibit excellent chemical resistance, which makes fabrication process of back contact solar cells easier.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1061-1063, Wafer slicing by diamond wire saws will substantially contribute to cost reduction in mono c-Si (mcSi) wafer production provided the coolant supply technology is economically viable. Aqueous (water based) coolants appear to be generally advantageous. Meanwhile new coolants with more attractive prices can be found on the market. The ways how to apply a coolant and how to handle spent coolants need to be optimized to achieve further improvements. “LOW-FLOW” and “HIGH- FLOW” coolant mode, both with or without coolant regeneration and reuse, should be distinguished. A detailed economic comparison clearly shows that “HIGH-FLOW” coolant usage, imperatively combined with reclaim of spent coolant, lowers the impact of coolant supply on wafer production costs significantly. Generally, “HIGH-FLOW” application of aqueous coolants in collaboration with coolant regeneration/ reuse is preferable to any “LOW-FLOW” mode if disadvantages due to continuously increasing solid load during one cut are tolerable, and if spent coolant is regenerated and reused. Coolant regeneration and reuse are essential prerequisites for cost-efficient coolant supply regardless of the mode of coolant application. Without regeneration, even “high-flow” mode is inefficient.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 896-900, In this work our target is to obtain low surface emitter concentration with Gaussian profilesdue to that have a strongly effect on solar cell efficiency. Two kinds of phosphorus profiles were proceed experimentally, the first emitter profile is obtained with only pre-deposition process for various diffusion temperature and the second emitter profile by adding a drive-in after introducing thermal dry oxidation step after diffusion process for various diffusion temperature. Diffusion profiles after Dry oxidation process predict a reduction in surface recombination due to removing the inactive phosphorus layer that is play as recombination centers. Both Voc and Jsc simulation results increased after the emitter surface concentration has been reduced with the thermal oxidation process.The Voc and Jscvaluescalculated by PC1D, using a Gaussian model with values of the emitter surface concentration Ns and sheet resistance for the corresponding values of depth junction. The first emitters show maximum efficiencies using Pc1D simulation program about (≈16-19%) with emitter surface concentration Ns = (0.8-3) x1020cm-3 and junction depth range (0.35-0.6)μm. For second emitters the surface concentration is reduced with the same diffusion parameters and show improvement of the maximum efficiencies ( ≈ 20-22.5%) with surface doping concentration s = (0.6-2) ×1019 (cm-3) and junction depth range of (1.3-2.3)μm. Silicon solar cell performance and parameters are improved after the thermal dry oxidation process and become more efficient.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 683-689, Formation of electrical conductors by wet chemical metallization is well-known in the electronics industry, with decades of implementation in the fabrication of printed circuit boards and microelectronics. However, its usage in the photovoltaic industry is still in its early stages. As the solar cell fabrication process matures, wet chemical copper metallization will move from acceptable, to preferred, to required. Relative to screen printed silver paste, copper allows higher aspect ratio, self-aligned conductors, and compatibility with increasingly complex materials and processes. Many of the highest efficiency cell architectures already require, or benefit from, wet chemical metallization. Future commodity cells are predicted to require copper conductors, due to the need to continually improve efficiency while simultaneously driving costs lower. This paper is a review of the current status of wet chemical metallization in the photovoltaic space, and a prospectus for where the technology trends are leading. Also included is a brief history of plating in PV, as well as its advantages, challenges, application to specific cell types, and path to mass adoption.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 598-601, In this work, we present promising simple method for a modification of optical response in c-Si solar cells. In this approach the spectral dependence of the optical reflectance is intentionally changed by strictly controlled electrochemical etching of the surfaces. It is demonstrated that the etching produces a layer with randomly ordered silicon nanowires (SiNW) that changes the optical response of the surface. The change in the reflectance spectrum depends on the dimensions of the SiNWs that are intentionally tuned by controlling the conditions of the etching. Our experimental results demonstrate that a maximum appears in the reflectance spectrum of c-Si surface with the SiNW in the interval of the visible wavelengths. The position of the maximum depends on the length of the SiNW and can be varied within entire interval of the visible light. We describe the relationships between the etching conditions, the properties of the SiNW layer and the optical response in this report. The technological parameters that produce the most significant effect on the dimensions of the SiNW and the reflectance are identified.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1053-1056, The surface morphology of and subsurface damage in silicon wafers produced by fixed abrasive diamond wire sawing influence the mechanical strength of photovoltaic silicon solar cells. One approach to cutting wafers with favorable surface and subsurface characteristics is using diamond wires made with different grit shapes. In this paper, we study mono-crystalline silicon wafers cut by wires with two nominally different grit shapes (denoted A and B), to determine the effect of grit shape on the wafer surface morphology, roughness, subsurface damage, and fracture strength. It is found that the surface morphology of wafers cut by wire A exhibits more ductile grooves while the wafer surface cut by wire B exhibits more brittle fracture. The surface roughness data show that wafers cut by wire A have lower surface roughness than those cut by wire B. However, biaxial flexure tests on laser-cut wafer coupons show that the wafers cut by wire A have lower fracture strength than those cut by wire B. The subsurface damage in wafers cut by wire A consists of fewer but longer median cracks than those cut by wire B, which has shallow median and lateral cracks. We hypothesize that the observed variation in fracture strength results from the dominance of the subsurface condition over the surface condition.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 958-960, One common requirement for all frontside contacted cells is to utilize fine finger lines with good conductivity. An established technique already proven in mass production is Fine Line Double Printing, able to deliver finger widths of 40-45 μm and an Aspect Ratio of 0.5. In this paper an evolution of this approach is described, where: 1) busbars are printed separately from fingers and 2) fingers are printed twice with the same screen. This patented concept allows for increased printing consistency and a greatly simplified process in terms of screens and tool.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 443-446, We fabricate n-type rear emitter cells with a boron silicate glass (BSG) layer deposited by means of plasma-enhanced chemical vapor deposition (PECVD). The multi-functional stack consisting of the BSG layer and a PECVD silicon nitride (SiNz) capping layer acts both as a boron diffusion source and as the rear side passivation achieving saturation current densities of J0=40 fA/cm². For solar cell fabrication, the rear emitter is diffused from the BSG/SiNz stack while the front surface field (FSF) is diffused from POCl3 gas in a co-diffusion process. We present a novel n+ n p+ solar cell concept and name it BiCoRE (Bifacial Co-diffused Rear Emitter) cell that applies a screenprinted Al grid on the rear side for bifaciality. The process flow and complexity of the BiCoRE cells are very similar to industrial Passivated Emitter and Rear Cells (PERC). The BiCoRE cells processed on the very first batch demonstrate conversion efficiencies up to h=20.6% when illuminated from the front side, up to 16.1% rear-side efficiency and a bifaciality of 78%.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 615-617, Laser techniques have been applied in mass production of silicon based crystalline solar cell, such as PERC and n-PERT. The detail laser work plays an important role in the fabrication of high efficiency solar cells. On the other hand, the conventional Ag screen-printed contacts usually have high contact resistance and lead to junction shunting issue during the post firing process. The Ag screen printing can be replaced with Ni/Cu plating to reduce the production cost of solar cells. Before Ni/Cu plating, the patterned removal of SiNx is operated by 532nm green laser. However, there are still drawbacks discovered during laser process. It is observed that if the output energy and focus are not suitable, there is silicon nitride(SiNx) left on the surface or damage of wafer discovered by scanning electron microscope (SEM). By the way, the characterization of SiNx residue is identified by Energy Dispersive Spectrum(EDS). Based on the measurements, it is also believed that the low specific contact resistance(c) and high cell efficiency depend on the Ni/Cu contacts at interface strongly. The filling factor(FF) and cell efficiency both indeed correspond to variation of the opening area and metallization. According to our investigation, the optimization of laser ablation process is available and the removal of SiNx residue is under control effectively.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 780-782, The passivation properties of a SiNx/SiOxNy stack on n-type Czochralski (Cz) Si wafer and n-type emitter with phosphorus diffusion are determined. The SiNx/SiOxNy stack shows considerably better passivation properties on both n-type Si wafer and n-type phosphorus diffused emitters relative to the single SiNx layer after a firing process. The improvement is more distinct for emitters with higher sheet resistance. In addition, the stability of the SiNx/SiOxNy stack passivation is also investiga-ted. The passivation stability during extended illumination reveals similar behavior as that of a single SiNx layer. Illumination at one-sun starts to degrade the passivation quality after an initial increase. Heating at 250°C reduces the lifetime as well, but only on fired samples. The passivation quality of the as-deposited stack, however, can be improved during the heating process, most likely due to hydrogen in-diffusion. Moreover, the degradation can be largely recovered by further thermal activation. Minimal degradation was observed for samples stored in the dark. largely be recovered by further thermal activation. Minimal degradation was observed for samples stored in the dark.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 1021-1024, The present work investigates the silica slip cast crucible’s role as a contamination source of multicrystalline silicon during directional solidification. The diffusivity of iron in the crucible material and quartz glass was quantified at three different temperatures (1100, 1200 and 1300 °C). Samples of quartz glass and samples of a silica slip cast crucible were heat treated in contact with solid steel. The diffusion profile of iron in quartz glass was obtained with line scans using an Electron Probe Micro Analyser. The diffusion profile of iron in the silica crucible was obtained with Semi-quantitative X-ray mapping and image analysis. The concentration profiles of iron were fit to the solution of the diffusion equation and the temperature independent diffusion coefficients could also be obtained. The diffusivity of iron in both the crucible and quartz glass increased with temperature and the diffusivity was higher in the porous crucible material than in the denser quartz glass. The temperature independent diffusion constants and activation energies were estimated to be 1,12*10-4 cm2/s and 1,52 eV for the crucible, respectively, and 8,1*10-5 cm2/s and 1,8 eV for the quartz glass, respectively. These results indicate that the impurity transport is strongly dependent on the crucible structure. The estimated transport parameters of iron through the crucible material were applied in a numerical model that predicts the contamination of silicon during directional solidification.

32nd European Photovoltaic Solar Energy Conference and Exhibition; 647-650, n-type solar cell concepts increasingly utilize emitter formation by diffusion from boron doped sources. Combining the advantage of n-type silicon material and bifacial cell architecture enables high-efficiency and versatile photovoltaics. In case of boron emitters, it was standard until now to form a metal-semiconductor contact by screenprinting Al containing Ag pastes. Instead of utilizing Al to enable Ag to form a sufficient contact with the risk in loss of VOC and FF, different glass compositions for pure Ag pastes were developed to form a contact with low impact on cell efficiency. In direct comparison this method in the first try already surpasses the performance of commercial Al containing Ag pastes in direct comparison. The experimental pastes show a distinctive gain in solar cell characteristics in contrast to commercial pure Ag pastes. In this case we reached an overall efficiency of 18.6% using pure Ag pastes. Contact resistivity values thereby range below 1-2 mcm² comparable to pure Ag pastes on n-type emitters and Ag/Al pastes on p-type emitters.