Plasma immersion ion implantation of boron for ribbon silicon solar cells (original) (raw)
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Progress in Photovoltaics: Research and Applications
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 implantation doses for sheet resistances between 110 and 160 Ω/sq. After metallization steps, the metal/emitter contact resistances were assessed, indicating that these emitters were compatible with a conventional metallization by screenprinting/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 Ω/sq. Promising performances while being integrated in n-PERT solar cells fully doped by PIII were demonstrated with efficiency of 20.8%.
19.3% Efficiency on P-Type Silicon Solar Cells by Pulsion® Plasma-Immersion Implantation
Energy Procedia, 2013
IBS and INES have recently demonstrated the strong relevance of the plasma-immersion ion implantation (PIII) technique to realise high efficiency silicon solar cells. The fabrication process, developed on 239 cm² p-type Cz-Si wafers, gives performances similar to those of classical ion beam implantation, with an efficiency improvement of 0.7% absolute with respect to classical POCl 3 -based emitters. Repeatability and robustness of the developed process have been validated. We give some information describing the different steps to achieve the homogeneous n-emitters by pulsed-PIII and present characterisation results showing which cell parameters are better than that of standard cells. Both high throughput and low cost of the immersion-plasma equipment would seriously challenge technologies developed by other companies in the ion-implantation field devoted to the PV market. Investigations to realise BSF, advanced emitters or IBC cells by this technique are now included in the roadmap.
Laser Annealed Boron Implanted Silicon Solar Cells
Photovoltaic Solar Energy Conference, 1978
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High-Throughput Ion-Implantation for Low-Cost High-Efficiency Silicon Solar Cells
Energy Procedia, 2012
This paper presents the use of ion-implantation for high-volume manufacturing of silicon solar cells. Ion-implantation provides a unique opportunity to obtain grid-parity because it simplifies the fabrication of advanced cell structures. It is shown in production that a streamlined ion-implantation process with homogeneous phosphorus doped emitter can raise the efficiency of 239 cm 2 p-base Cz cells by 0.8 % absolute, from 18.3 % to 19.1 %, while reducing the process sequence by one step relative to traditional POCl 3 process. Average production cell efficiency is about 18.6 % with maximum exceeding 19 %. Several advanced cell structures were fabricated in R&D using ion-implantation and screen printed contacts. The advanced p-base structure with ion implanted selective emitter and local Al-BSF resulted in an efficiency of 19.6 %. In addition, three different n-base cell structures were fabricated using boron (B) and phosphorus (P) implantation followed by in-situ front and back passivation during the implant anneal: the n-base cell with B emitter, passivated P-BSF with local contact and full metal back gave 19.2 % efficiency, the implanted n-base bifacial cell was 19 % efficient, and the n-base back junction cell with B emitter in the rear and P front surface field resulted in 19 % efficiency.
First solar cells on silicon wafers doped using sprayed boric acid
Semiconductor …, 2010
A new method for boron bulk doping of silicon ribbons is developed. The method is based on the spraying of the ribbons with a boric acid solution and is particularly suited for silicon ribbons that require a zone-melting recrystallization step. To analyse the quality of the material thus obtained, multicrystalline silicon samples doped with this doping process were used as substrate for solar cells and compared with solar cells made on commercial multicrystalline silicon wafers. The values obtained for the diffusion length and the IV curve parameters show that the method of doping with the boric acid solution is suitable to produce p-doped silicon ribbons for solar cell applications.
Progress in Photovoltaics: Research and Applications, 2014
In this paper, we report on commercially viable screen printing (SP) technology to form boron emitters. A screenprinted boron emitter and ion-implanted phosphorus back surface field were formed simultaneously by a co-annealing process. Front and back surfaces were passivated by chemically grown oxide capped with plasma-enhanced chemical vapor deposition silicon nitride stack. Front and back contacts were formed by traditional SP and firing processes with silver/aluminum grid on front and local silver back contacts on the rear. This resulted in 19.6% efficient large area (239 cm 2) n-type solar cells with an open-circuit voltage V oc of 645 mV, short-circuit current density J sc of 38.6 mA/cm 2 , and fill factor of 78.6%. This demonstrates the potential of this novel technology for production of low-cost highefficiency n-type silicon solar cells.
Laser-Annealed, Implanted Boron Emitters for B-BSF Silicon Solar Cells
Energy Procedia, 2012
Boron (B) emitters are required in an increasing number of silicon solar cells technologies, each of them requires an appropriate emitter profile. This work aims at investigating laser thermal annealing (LTA) from implanted B as a versatile approach for B-emitter processing compared to standard furnace annealing. Symmetrical p + /n/p + structures featuring various LTA B-emitters were characterized using the QssPC technique. Experimental results show that in contrast to thermally-diffused B-emitters, implied V oc of LTA emitters increases when their sheet resistance decreases. Numerical simulations suggest that the observed trend could be attributed to a reduction in the surface recombination velocity. LTA emitters were then integrated as B-BSF into silicon solar cells. Gains of 2 mV in V oc and 0.8 mA/cm² in J sc compared to Al-BSF were obtained, leading to an overall efficiency enhancement of 0.3 % abs .
Solar Cells on Silicon Ribbons Doped With Sprayed Boric Acid as a Doping Source
The method for boron bulk doping of silicon ribbons based on the use of sprayed boric acid as a doping source is particularly suitable for producing p-type silicon ribbons that require zone melting recrystallisation (ZMR). This paper reports on a test of the application of this method for the doping of multicrystalline material that was used as the base material for solar cells. The aim was to study the material deterioration due to the spray doping process. Analysis of solar cell performance, lifetime measurements and GDMS contaminants detection, suggest that the doping process with boric acid solution does not produce detectable deterioration of the material quality compared to the control (non-recrystalised) materials.
High-efficiency n-type silicon solar cells with front side boron emitter
2009
High-efficiency n-type PERL solar cells with a front side boron emitter passivated by ALD Al 2 O 3 are presented within this work. For the applied PERL cell design two variations have been employed: i) different boron emitters (deep / shallow) and ii) different dielectric layers for rear side passivation (thermal grown SiO 2 and PECVD SiN x ). Both, thermal grown SiO 2 as well as PECVD SiN x provide an effective passivation of the n-type rear surface with effective surface recombination velocities of 4 cm/s and 7 cm/s respectively. If the metalized rear side point contacts (with BSF) together with the recombination of the 1 Ω cm FZ base silicon are taken into account this results in saturation current densities of 30 fA/cm 2 and 37 fA/cm 2 respectively, limiting the open-circuit voltage (all recombination losses due to the front side are neglected) to 717 mV and 712 mV. The passivation of the boron emitter with ALD Al 2 O 3 results in an emitter saturation current density as low as 11 fA/cm 2 . Together with the losses at the rear side as well as the front side contacts this allows for an open-circuit voltage of the applied PERL solar cell design of ~700 mV. For n-type PERL solar cells featuring a lowly doped boron emitter as well as a SiO 2 passivated rear such a high open-circuit voltage (up to 703.6 mV) could be reached also at the device level, resulting in a conversion efficiency of 23.4%. Also for the PERL solar cells featuring a high surface concentration boron emitter with a PECVD SiN x passivated rear, i.e. first steps towards an industrial structure, still a high conversion efficiency of 21.8% could be achieved. All cells have been shown to be perfectly stable under illumination at 1 sun.