Bifacial Solar Cells on Multi-Crystalline Silicon with Boron BSF and Open Rear Contact (original) (raw)
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Analysis of thin bifacial silicon solar cells with locally diffused and selective back surface field
Materials Research, 2014
The aim of this work is to present the development and comparison of thin n + pp + industrial bifacial silicon solar cells produced with the local screen-printed Al back surface field (BSF) to those with the selective BSF doped with aluminum-boron. To produce solar cells with selective BSF, the boron diffusion based on spin-on dopant was introduced in the process sequence. The thin SiO 2 layer (10 nm) thermally grown did not produce good passivation on the rear face and wafers were contaminated during aluminum diffusion in the belt furnace. The implementation of selectively doped BSF improved the efficiency by reflecting minority charge carriers and the wafer contamination by belt furnace was compensated by boron diffusion. The bifacial solar cells with B-Al selective BSF achieved an efficiency of 13.7% / 8.9% (front / rear illumination) and presented lower sensitivity to the belt furnace processing and to the quality of the rear surface passivation.
High efficiency screen printed bifacial solar cells on monocrystalline CZ silicon
We present industrialized bifacial solar cells on large area (149 cm 2 ) 2 cm CZ monocrystalline silicon wafers processed with industrially relevant techniques such as liquid source BBr 3 and POCl 3 open-tube furnace diffusions, plasma enhanced chemical vapor deposition (PECVD) SiN x deposition, and screen printed contacts. The fundamental analysis of the paste using at boron-diffused surface and the bifacial solar cell firing cycle has been investigated. The resulting solar cells have front and rear efficiencies of 16.6 and 12.8%, respectively. The ratio of the rear J SC to front J SC is 76.8%. It increases the bifacial power by 15.4% over a conventional solar cell at 20% of 1-sun rear illumination, which equals to the power of a conventional solar cell with 19.2% efficiency. We also present a bifacial glass-glass photovoltaic (PV) module with 30 bifacial cells with the electrical characteristics.
20.1% Efficient Silicon Solar Cell With Aluminum Back Surface Field
IEEE Electron Device Letters, 2000
We present a standard p + pn + solar cell device exhibiting a full area aluminum back surface field (BSF) and a conversion efficiency of 20.1%. The front side features a shallow emitter which has been exposed to a short oxidation step and reduces the dark emitter dark saturation current density j 0e to 160 fA/cm² on a textured surface. The front contact is formed by light induced nickel-and silver-plating.
J. Nano- Electron. Phys., 2023
In this study, experiments on the alloying process from screen-printed aluminum (Al) pastes on silicon surfaces for solar cell applications were conducted. We investigated the effect of wafer thickness and screen-printing mesh counts on the Al back surface field (Al-BSF) properties of Czochralski silicon (Cz-Si) solar cells Screens with different mesh counts (150, 200 and 400 mesh) were used to print variable amounts of Al paste (7, 9.4 and 12 mg/cm 2). Rapid thermal annealing (RTP) annealing processes of 750 °C and 800 °C for 60 s were applied to form AL-BSF. SEM micrographs showed the formation of a rough surface with 4.31 m alloying layer over bulk Si wafer. ECV and SIMS analysis showed that an annealing peak temperature of 750 °C and an amount of Al paste of 12 mg/cm 2 are suitable for the creation of an optimal Al-BSF. This work revealed that Al-BSF properties are strongly affected by the mesh counts used in screen-printing of Al paste. However, no monotonic relationship was noticed with the wafer thickness. The mask with 150 meshes allowed to obtain high Al concentrations at the surface, maximum diffusion depth and longer average lifetimes of charge carriers.
A Novel Low-Cost Method for Fabricating Bifacial Solar Cells
Conference Record of the IEEE Photovoltaic Specialists Conference
In this work we propose and demonstrate a novel and cost-effective method to fabricate bifacial cells with conventional homojunction architecture. The method combines benefits of lithography-less, self-aligned patterning during deposition of antireflective coating (ARC) and simultaneous metallization of both surfaces aided by electroplating. We have fabricated a conventional diffused n + pp + junction bifacial solar cell on a monocrystalline silicon (c-Si) substrate using this method. Electrochemically grown nickel is used to simultaneously form front and back electrodes. The bifacial solar cell fabricated with an un-optimized process has a front and rear efficiencies (under AM1.5G one sun illumination) of 12% and 8.66%, respectively. Part of the low performance of the cell is attributed to poor quality of the passivation layer and the post deposition annealing to reduce pinholes in deposited SiN x layer to prevent parasitic plating.
IEEE Journal of Photovoltaics, 2011
This paper describes the cell design and technology on large-area (239 cm 2) commercial grade Czochralski Si wafers using industrially feasible oxide/nitride rear passivation and screenprinted local back contacts. A combination of optimized front and back dielectrics, rear surface finish, oxide thickness, fixed oxide charge, and interface quality provided effective surface passivation without parasitic shunting. Increasing the rear oxide thickness from 40 to 90Å in conjunction with reducing the surface roughness from 1.3 to 0.2 μm increased the V o c from 640 mV to 656 mV. Compared with 18.6% full aluminum back surface field (Al-BSF) reference cell, local back-surface field (LBSF) improved the back surface reflectance (BSR) from 65% to 93% and lowered the back surface recombination velocity (BSRV) from 310 to 130 cm/s. Twodimensional computer simulations were performed to optimize the size, shape, and spacing of LBSF regions to obtain good fill factor (FF). Model calculations show that 20% efficiency cells can be achieved with further optimization of local Al-BSF cell structure and improved screen-printed contacts.
Continued Development of All-Back-Contact Silicon Wafer Solar Cells at ANU
The collaboration between the Solar Energy Research Institute of Singapore (SERIS), Trina Solar and ANU is progressing well, and ANU has already developed all-back-contacted (ABC) silicon wafer cells with best one-sun efficiencies of 21.2% and 22.1% on FZ material, when measured with the aperture areas of 16 cm 2 (includes busbars) and 13 cm 2 (excludes busbars) respectively. This paper presents the continuing development of ABC cells targeting the efficiency of 23.5% on 16-cm 2 cell area. Further developments such as optimising front surface field (FSF), rear diffusion, anti-reflection coating (ARC), and incorporation of lithographically aligned metal contacts were sity (J oe) of the FSF by 22 fA/cm 2. The optimised thickness of anti-reflection coating (ARC) PECVD SiN x further reduces the average reflectance across the wavelength range of 300 to 1200 nm by about 4%. Incorporation of aligned metal contacts and heavier rear 2. The above optimised improvements have increased the efficiency of the champion ABC cell by 0.5% absolute. In addition, we present further refinements in areas of texturing; FSF passivation; electrical shading loss in terms of cell pitch, bus-bar and base doping; and metallisation to aim for the 16-cm 2 ABC cells with the conversion efficiency > 22% in the near term.
15% multicrystalline n-type silicon screen-printed solar cells with Al-alloy emitter
2008 33rd IEEE Photovolatic Specialists Conference, 2008
Long diffusion length is essential to reach high efficiencies (>15%) on rear-junction solar cells. As a rule of thumb the minority carrier diffusion length should be at least three times as long as the wafer thickness. Thanks to the smaller capture cross-section of impurities measured in n type material, n-type silicon can exhibit a diffusion length exceeding 600 IJm even in its multi-crystalline form. High efficiency rear-junction cells become feasible at reasonable cost with wafers as thick as 200 IJm. The development of the p+ emitter on the rear is essential for this type of cell, and AI alloying is one of the techniques of choice to realize it. After optimizing the emitter, we obtained very good values for Voc (-615 mV) and FF (>80%). Afterwards, focus was laid on improving the short circuit current. This was achieved by an optimization of the phosphorus-diffused front-surface field, and by thinning down the wafers. These two actions had the consequence of increasing independently of each other the Jsc by 2.3 mAcm-2 for the optimization of the front-surface field, and by 3 mAcm-2 when wafer thickness decreased from 300 IJm to 150 IJm. The characteristics obtained are observed to be extremely dependent on the wafer quality, which varies a lot along the ingot. An efficiency of 15.0% (30.7 mAcm-2 ) was reached on rear-junction n-type 150-lJm thick 5x5-cm 2 2.5-ohms.cm multi-crystalline Si.
Aluminium BSF in silicon solar cells
Solar Energy Materials and Solar Cells, 2002
The purpose of this work is to develop a back surface field (BSF) for industrial crystalline silicon solar cells and thin-film solar cells applications. Screen-printed and sputtered BSFs have been realised on structures which already have a n + p back junction due to the diffusion of the phosphorus in both faces of the wafer during solar cell emitter elaboration. Rapid thermal annealing temperatures from 7001C to 10001C have been used. Thickness of the BSF has been measured by SIMS and confronted to the theoretical expected value and simulations. Electrical and optical measurements have been done in order to characterise the BSF. For 250 mm thick industrial solar cells, 6% relative increase in photocurrent has been reached. r
REFLECTS – a European CRAFT project for the development of a bifacial silicon solar cell module
The objective of the REFLECTS project (Novel bifacial single substrate solar cells utilising reflected solar radiation) is the development of a cost effective, high efficiency bifacial silicon solar module exploiting the light reflected from behind the cells for energy generation. A bifacial rear contact silicon solar cell using a simple processing sequence is developed. Mechanical grinding is deployed for the definition of the emitter and base contact regions. The rear surface structure is then utilised as a mask for the self-aligned metallization of the bifacial rear contact cells applying the OECO (obliquely evaporated contacts) -technique. We achieved an efficiency of 20.5 % under illumination from the non-metallised cell side whereas the efficiency is as high as 17.0 % when illuminated from the metallised side. A string of 5 bifacial cells is mounted and encapsulated on a non-concentrating reflector developed within the project. Applying the reflector enhances the short circuit current by 38 %.