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This work focuses on a passivating contacts technology for crystalline silicon (c-Si) wafers based on ultra-thin (15nm) poly-crystalline Silicon (poly-Si) on silicon oxide (SiOx) stacks. Combined with standard TCO (Transparent Conductive Oxide) layers in a simplified solar cells fabrication process, photovoltaic (PV) conversion efficiencies approaching 22% are obtained on cast-mono wafers. This technology is also shown to be compatible with different TCO layers, depending on the post metallization annealing step. This so called "High Temperature Silicon Heterojunction" structure is therefore very promising for high efficiency solar cells processes at lower cost.

We report in this paper on the development of thin passivating poly-crystalline Silicon (poly-Si) on silicon oxide (SiO x ) stacks, with poly-Si films deposited by Low Pressure Chemical Vapor Deposition (LPCVD) and doped by Plasma Immersion Ion Implantation (PIII). Such advanced passivating contacts can be integrated, in combination with In-free TCO layers, at both the front and rear sides of high efficiency solar cells via simple fabrication processes. High iV oc values close to 700 mV were obtained just after the annealing step required for the poly-Si crystallization and dopant activation. The first cell integration demonstrated photovoltaic (PV) conversion efficiencies of 21.2% for this approach. Moreover, we demonstrated that the poly-Si layers elaboration process provides efficient external gettering effects on cast-mono wafers, with bulk carrier lifetime exceeding 3 ms after the poly-Si (n+)/SiO x stack formation. These results are therefore encouraging for the use of low cost, low carbon footprint Si materials, in double-side passivated contacts high efficiency cell structures.

This paper reports on an innovative way for the hydrogenation of transparent conductive oxide (TCO) layers deposited by magnetron sputtering. These hydrogenated films offer the possibility to increase the performances of crystalline silicon (c-Si) solar cells using passivating contacts technologies. Plasma Immersion Ion Implantation (PIII) of Hydrogen is shown to improve both surface passivation and electrical properties of TCO layers depending on the post-implantation annealing steps. A double effect is obtained through this annealing process: (i) TCOs electrical conductivity improvement and (ii) a better passivation of the c-Si surface possibly due to the enhancement of the hydrogen diffusion.

International audience; Ion implantation is a suitable and promising solution for the massive industrialization of boron doping, which is a crucial process step for most next-generation solar cells based on crystalline silicon (c-Si). However, the use of ion implantation for boron doping is limited by the high temperature (in the 1050°C range) of the subsequent activation anneal, which is essential to dissolve the boron clusters and reach a high-emitter quality. In this work, we propose the use of plasma-immersion ion implantation (PIII) from B$_2$ H$_6$ gas precursor instead of the standard beamline ion implantation (BLII) technique to decrease this temperature down to 950°C. PIII and BLII boron emitters were compared with annealing temperatures ranging from 950°C to 1050°C. Contrary to BLII, no degradation of the emitter quality was observed with PIII implants annealed at 950°C along with a full activation of the dopants in the emitter. At 1000°C, emitter saturation current densities (J$_{0e}$) below 21 fA/cm$^2$ were obtained using the PIII technique regardless of the tested implanta-tion doses for sheet resistances between 110 and 160 $\Omega$/sq. After metallization steps, the metal/emitter contact resistances were assessed, indicating that these emitters were compatible with a conventional metallization by screen-printing/firing. The PIII boron emitters' performances were further tested with their integration in n-type passivated emitter rear totally diffused (PERT) solar cells fully doped by PIII. Promising results already show a conversion efficiency of 20.8% using a lower annealing temperature than with BLII and a reduced production cost. KEYWORDS annealing temperature, B$_2$ H$_6$ plasma, boron doping, n-type PERT solar cells, plasma-immersion ion implantation, silicon solar cells We report a new way to activate implanted boron emitter at low temperature that is the use of plasma-immersion ion implantation (PIII) from B$_2$H$_6$ plasma. A full activation of the emitter at 950°C was observed even for a high implantation dose corresponding to a sheet resistance of 112 $\Omega$/sq. Promising performances while being integrated in n-PERT solar cells fully doped by PIII were demonstrated with efficiency of 20.8% % using a lower annealing temperature than with BLII and a reduced production cost.

International audience; Polysilicon (poly-Si) based passivating contacts are promising to improve silicon solar cells conversion efficiency. However, the use of Transparent Conductive Oxides (TCO) has to be considered to improve lateral conductivity while maintaining good optical and surface passivation properties especially for bifacial devices. In this work different Aluminum-doped Zinc Oxide (AZO) based layers have been investigated after high temperature firing steps to contact Phosphorus-doped poly-Si layers. Contact resistivity below 100 mΩ.cm$^2$ at the AZO/n$^+$ poly-Si interface and stable implied open circuit voltage values (> 715 mV) have been obtained for firing temperatures from 550°C to 900°C. Moreover, the use of capping layers allows to maintain highly conductive AZO layers upon annealing. This novel high temperature contacting method via indium-free TCOs, is particularly interesting for the industrial integration of poly-Si based passivated contacts and provides new perspectives for advanced homojunction solar cells.

The use of plasma immersion ion implantation (PIII) is a relevant approach for the development of advanced solar cells technologies at lower cost (€/W p ). In this paper, we report on the development of homogeneous boron (B) doping of n-type crystalline silicon (cSi) substrate by the PIII technique. Using diborane (B 2 H 6 ) as gas precursor, various doping profiles were identified fitting the requirements for boron-doped emitters in n-type PERT solar cells. Particularly, saturation current density (J 0e ) of 50 fA/cm 2 were achieved on symmetrical samples for a 94 Ω/sg textured B-emitter passivated with SiO 2 /SiN stack. Bifacial n-type Passivated Emitter Rear Totally-diffused (n-PERT) solar cells were fabricated using the PIII technology and conversion efficiencies up to 19.8% on 239 cm 2 Cz-Si wafers were obtained. As a consequence, these results indicate that PIII can compete with beamline technology but will have lower running cost. It is therefore a promising technology to create high efficiency cSi solar cells.

International audience; Polysilicon (poly-Si) based passivating contacts are promising to improve silicon solar cells conversion efficiency. Thin poly-Si layers usually feature high sheet resistances compared to conventional diffused junctions. Therefore the use of Transparent Conductive Oxides (TCO) has to be considered to improve lateral conductivity while maintaining good optical and surface passivation properties. Standard sputtered Indium Tin Oxide (ITO) can alter the poly-Si passivation properties. In this work different TCO-based contacts have been investigated (various materials and deposition techniques) in order to contact phosphorus-doped poly-Si layers (n+ poly-Si). The TCO-deposited samples experienced both low and high temperature annealing steps. Implied open circuit voltage above 730 mV and contact resistivity below 50 mΩ.cm2 at the TCO/n+ poly-Si interface have been obtained for both high and low temperature approaches. Thus such novel structures are very promising to contact poly-Si layers.

Since several years, the use of Beamline ion implantation has been proven to allow optimization of doping profiles needed for the fabrication of crystalline silicon (c-Si) solar cells while simplifying the process flow. Nevertheless the cost and complexity of such tools, associated to the difficulty to keep a small thermal budget to make high quality Boron doping for N-type cells, has slowed down the industrial introduction of ion implantation in high volume solar cell fabrication fabs.Thanks to an implant time independent to the implanted surface, and a simple tool architecture, Plasma Immersion Ion Implantation (PIII) offers an economically efficient alternative to Beamline Ion Implantation.In this paper, after having presented PULSION®-Solar, the IBS PIII tool dedicated to solar cell fabrication, we will demonstrate state of the art characteristics on different cells type either on c-Si but also on multi crystal Si where the beneficial gettering capability allowed by POCl 3 is also obtained using PIII phosphorus implantation. We will also show how the PIII doping process, thanks to its unique energy distribution, can even be more efficient than beam line, especially for boron doping, allowing lower thermal budget and co-anneal with phosphorus, simplifying even more the process flow for n-type PERT solar cells.

Session 6: Process Integration and Low-cost Manufacturing; International audience; A key step to achieve high conversion efficiencies for silicon solar cells is the junction formation. Plasma Immersion Ion Implantation (PIII) enables fine variations of the surface dopant concentration and depth of the doping profiles. Since no “dead-layer” with electrically inactive dopant species remains after an activation annealing step, high electrical quality of doped regions can easily be performed. We studied whether advanced Phosphorus emitters obtained via PIII could be optimized to increase p-type crystalline silicon (c-Si) solar cell performances. The doping profiles were tuned by changing ion dose and post implantation activation annealing temperature (Tanneal). A detailed analysis of carrier recombination in the different part of Al-BSF solar cells has been performed. Thus, saturation current densities (J0) were extracted (passivated emitter J0e,passivation, metallized emitter J0e,metallization, c-Si bulk and Back Surface Field J0,bulk+BSF) by coupling IC-QssPC and Suns-Voc measurements on specific test structures. An increase in Voc and Jsc was obtained by lowering the ion dose for a given Tanneal, whereas Voc, Jsc and the Fill Factor (FF) were improved by lowering Tanneal for a given dose. In the first case, photovoltaic (PV) conversion efficiencies did not change because of an increase in series resistance. However in the second case, they were increased by 0.2% absolute by reducing Tanneal from 850°C to 800°C, with a high FF value of 79.3% despite a relatively high emitter sheet resistance (115 Ω/square).

International audience; This study explores the needed properties of Transparent Conductive Oxides (TCOs) for bifacial homojunctionsolar cells with potentially passivated contacts. TCO layers with different electrical and optical properties have been testedon both sides of n-type homojunction cells. The high lateral conductivity provided by the diffused emitter and back surfacefield (BSF) greatly reduces the constraints on TCO electrical properties in such structures. An understanding of the requiredproperties of TCO for advanced homojunction applications is given. Hence different O2-rich Indium Tin oxide (ITO) layersare analyzed optically and electrically before being implemented in homojunction solar cells to evaluate their influence onthe device performances. All in all moderately conductive TCOs are shown to be suitable for such applications, allowingbetter optical properties without inducing resistive losses in the devices.

A simple process for the fabrication of selective emitter structures on n-PERT cells is investigated, using shallow Boron emitters obtained by ion implantation. By tuning the emitter doping process parameters, J 0e values as low as 10 fA.cm -2 have been obtained with highly resistive profiles. Laser overdoping processes from AlO x passivating layers are tested on these profiles to locally increase the emitter conductivity and allow better contact properties. Through this process the emitter sheet resistance and doping profile may be locally controlled with a limited impact on the J 0e values.

In this study, fabrication of monolithic triple junction (3J) GaInP/AlGaAs/Si solar cells is reported by different wafer bonding approaches: (i) the most straightforward, direct GaAs/Si wafer bonding; (ii) an innovative 2-step approach combining epitaxy of GaAs bonding layer on Si cell followed by GaAs/GaAs direct wafer bonding; and (iii) Surface-Activated GaAs/Si wafer Bonding (SAB). Bonding interfaces properties are comparatively studied, and the performance of resulting III-V on Si triple junction devices is examined. Open-circuit voltages close to 2.9V are obtained in all cases, but large differences in fill factors between the bonding methods are observed, probably due to the presence of an oxide layer.

session poster (I43); International audience; Monolithic two-terminal III-V on Si dual-junction (2J) solar cells were fabricated by means of Surface-Activated direct wafer Bonding (SAB). Al 0.2 Ga 0.8 As single-junction cells are grown on GaAs substrate by Metal-Organic Vapor Phase Epitaxy (MOVPE) and bonded at room temperature to independently fabricated Si solar cells. The n+-GaAs//n+-Si bonding interface is characterized by Transmission Electron Microscopy (TEM) revealing a 2-3 nm thick amorphous interlayer. The performance of the 1 cm 2 tandem cells, designed for low concentration applications, was studied by External Quantum Efficiency (EQE) and J-V measurements showing a power conversion efficiency of 17% under one-sun AM1.5G spectrum. To our knowledge, this is the highest efficiency ever reported for a wafer-bonded 2J III-V on Si solar cell. Limitations to performance have been identified and therefore higher efficiencies are expected.

International audience; Production costs and energy efficiency are the main priorities for the photovoltaic (PV) industry (COP21 conclusions). To lower costs and increase efficiency, we are proposing to reduce the number of processing steps involved in the manufacture of N-type Passivated Rear Totally Diffused (PERT) silicon solar cells. Replacing the conventional thermal diffusion doping steps by ion implantation followed by thermal annealing allows reducing the number of steps from 7 to 3 while maintaining similar efficiency. This alternative approach was investigated in the present work. Beamline and plasma immersion ion implantation (BLII and PIII) methods were used to insert n-(phosphorus) and p-type (boron) dopants into the Si substrate. With higher throughput and lower costs, PIII is a better candidate for the photovoltaic industry, compared to BL. However, the optimization of the plasma conditions is demanding and more complex than the beamline approach. Subsequent annealing was performed on selected samples to activate the dopants on both sides of the solar cell. Two annealing methods were investigated soak and spike thermal annealing. Best performing solar cells, showing a PV efficiency of about 20%, was obtained using spike annealing with adapted ion implantation conditions.

The interest of using Transparent Conductive Oxides (TCO's) as alternative contact layers on crystalline silicon (c-Si) homojunction solar cells is discussed in this paper. To evaluate the contact quality, vertical conductivity as well as passivation properties have been measured on symmetrical test structures showing either n+ or p+ surface doping, covered with an Indium Tin Oxide (ITO) layer deposited by sputtering. The influence of annealing steps between 200°C and 700°C on the TCO/c-Si and Metal/TCO contact properties are shown. Using a direct TCO contact on both sides, an efficiency of 15.4% is obtained on 156×156 mm2 n-type solar cells, limited by the high saturation current density of the ITO contact. To avoid recombinations at the TCO/c-Si interface, another deposition method for the TCO (with lower surface damage) should be used.

This study reports on the p-type a-Si:H emitter layer of silicon heterojunction (Si-HJ) solar cells and its contacting scheme. The influence of the ratio between p-type a-Si:H emitter width and its contact width is checked on Interdigitated Back Contact (IBC) Si-HJ both experimentally and by 2D modelling. A low emitter contact fraction value is found to be detrimental to the IBC Si-HJ cells efficiency due to distributed series resistance effects. This not only limits the cell fill factor (FF) but also its short circuit current density (Jsc). By increasing the emitter contact fraction an efficiency of 12.7% is obtained on 25 cm2 IBC Si-HJ solar cells. New B-doped a-Si:H emitter layers and contacts are also developed on inverted Si-HJ cells. Depending on the a-Si:H conductivity, we observe a great impact of the contact material on Si-HJ cells performance (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Modelling and experimental results on IBC SHJ solar cells are presented in this paper. Different rear emitter designs are studied by 2D simulation and tested on experimental devices. IBC SHJ cells are fabricated with the SLASH process based on laser patterning steps, and the performance of such devices is shown to be limited by the rear emitter geometry (contacting scheme and total emitter fraction). On one hand IBC SHJ cells have to be carefully designed concerning the contacting scheme due to distributed series resistance effects. On the other hand SHJ technology allows a very high surface passivation level, and this reduces the influence of the emitter fraction on the cells performances.

This work reports on the elaboration of a new industrial process based on laser selective ablation of dielectric layers for Interdigitated Back Contact Silicon Heterojunction (IBC Si-HJ) solar cells fabrication. Choice of the process is discussed and cells are processed to validate its performance. A pulsed green laser (515nm) with 10-20ns pulse duration is used for hydrogenated amorphous silicon (a-Si:H) layers patterning steps, whereas metallization is made by screen printed. High Open-Circuit Voltage (Voc=699mV) and Fill Factor (FF=78.5%) values are obtained simultaneously on IBC Si-HJ cells, indicating a high surface passivation level and reduced resistive losses. An efficiency of 19% on non textured 26 cm² solar cells has been reached with this new industrial process.

In this study a novel high efficiency crystalline silicon (c-Si) solar cell concept is presented. It combines Interdigitated Back Contact (IBC) structures with Silicon Heterojunction (Si-HJ) technology through the use of Laser assisted patterning steps. The SLASH (Structuring by Laser Ablation of Silicon Heterojunction) IBC cell shows a simplified geometry and a fabrication process compatible with mass production. SLASH IBC cells have been fabricated using optimized parameters for a-Si:H layers patterning and screen printed metallization. The c-Si surface morphology (polishing and texturation process) is shown to have a great impact on the cells parameters. Almost the same cell performances are obtained on alkaline and chemical-mechanical polished surfaces. An efficiency of 19.0% has been obtained on 5*5 cm2 devices proving the high efficiency potential of this simplified IBC structure.

In this work, we present our recent technological improvements realized on 148.5cm2 amorphous/crystalline double heterojunction solar cells. In particular, we have transferred our old solar cells fabrication process to an integrated JUSUNG large area cluster (PECVD/ MOCVD/ PVD). An optimization of all the fabrication steps separately, as well as a careful preparation of the silicon wafer's surface has allowed us to obtain efficiencies up to 19.6 % on large area solar cells (148.5cm2). The homogeneity and reproducibility of the process developed has been demonstrated on several successive batches with all efficiencies measured over 19.2%. All the fabrication process is performed at temperatures

In this work, we have studied the scalability of our fabrication process for heterojunction solar cells up to 148.5cm2 total area. Double heterojunction devices were fabricated on both n- and p-type textured substrates using only doped (n) and (p) a-Si:H layers. ITO was used as anti-reflective coating and evaporated Aluminum as the metallic back contact. Finally, an Ag grid was screen-printed at the front side. Efficiencies higher than 16% have been obtained in both cases demonstrating the homogeneity and robustness of our fabrication process for larger substrates. Nevertheless, there is still room for improvement especially in terms of passivation, the V oc values are still low (≪640mV), though it is a promising result considering that no intrinsic layer has been used.

This study deals with the introduction of Point Contact technology to enhance the efficiency of Interdigitated Back Contact (IBC) Silicon Heterojunction (Si-HJ) solar cells. For the study of point contacted Emitter and Back Surface Field (BSF), respectively Rear emitter (RE) Si-HJ cells and conventional Si-HJ cells are fabricated with different contact area fractions and different Emitter and BSF layers. It is shown that point contact area fraction should be above 16% to avoid performance losses for the different emitter stack. Emitter stack p-doped amorphous silicon on top of intrinsic amorphous silicon seems to be the most promising layer since it allows very high surface passivation level. Concerning point contacted BSF, further improvement of passivating stack and contact layer is still needed to allow an enhancement of cell efficiency. With an optimized geometry and further improvement of the passivating and contact layers, such structures may be suitable for an application on IBC Si-HJ devices.

In this work, we report on the fabrication and characterization of n-type c-Si solar cells whose p+ emitters are based on laser processed aluminum oxide/silicon carbide (Al2O3/SiCx) films. The p+ emitter is defined at the rear side of the cell and it consists of point-like laser-diffused p+ regions with a surface charge induced emitter in between based on the high negative charge located at the Al2O3/c-Si interface. These emitters are fabricated at low temperature (< 400 °C) and could be directly compared to silicon heterojunction emitters with the advantage that the deposition of a Transparent Conductive Oxide (TCO) film can be avoided, since they are based on p+/n c-Si homojunctions. Additionally, the involved films are transparent to the IR photons ( >1000 nm) that reach the rear surface of the cell resulting in an excellent back reflector. We fabricated solar cells with distance between p+ regions or pitch ranging from 200 to 350 µm with a front surface based on silicon heterojunction technology. Best efficiency (18.1%) is obtained for a pitch of 250 µm as a consequence of the trade-off between Voc and FF values.

International audience; This study reports on a new contact scheme for Silicon Heterojunction (Si-HJ) solar cells having Interdigitated Back Contacts (IBC). This new geometry with two metallization levels is used to avoid any electrical shading above the emitter and Back Surface Field (BSF) busbars. IBC Si-HJ solar cells with bi-level metallization are here compared experimentally to standard devices having a single-level contact scheme. Relative increases of 2% in Fill Factor (FF) and 8% in short circuit current density (Jsc) have been obtained with this optimized contact geometry on medium area solar cells (5x5cm(2)). Moreover, this technology can be used to increase the number of busbars on large area solar cells and therefore reduce series resistance effects.