Crystalline Silicon Solar Cell Engineering to Improve Fill Factor, Open Circuit Voltage, Short Circuit Current and Overall Cell Efficiency (original) (raw)
Related papers
Progress in the Development of All-Back-Contacted Silicon Solar Cells
N-type all-back-contact (ABC) silicon solar cells incorporating a simple oxide-nitride passivation scheme are presently being developed at the Australian National University. Having already achieved promising efficiencies with planar ABC cells [1], this work analyses the cell performance after integrating a surface texturing step into the process flow. Although the textured cells have significantly lower front surface reflection, the measured short-circuit current density is actually lower than that of the planar cells. Photoconductance decay data indicate the presence of high carrier recombination at the textured surface of the ABC cells, which are deposited with a stack of thermal oxide and LPCVD nitride. Further examination confirmed that high carrier recombination is due to stress induced by the LPCVD nitride on the peaks and valleys of the textured surface. Use of PECVD nitride instead of LPCVD nitride as an antireflection layer avoids the degraded carrier lifetime caused by the textured surface. Therefore, PECVD nitride should be a good substitute for constructing the oxide-nitride stacks of our future ABC cells.
Point Contact Technology for Silicon Heterojunction Solar Cells
Energy Procedia, 2012
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.
Dopant‐Free Back‐Contacted Silicon Solar Cells with an Efficiency of 22.1%
physica status solidi (RRL) – Rapid Research Letters, 2020
Contact recombination at the interface between the absorber material and the electrode interface is one of the most pressing issues limiting most photovoltaic technologies. Inserting a thin-film to prevent recombination while ensuring loss-free carrier extraction is a widely investigated route to fulfill this task. The multilayer films that include a low work-function metal such as calcium or magnesium simultaneously reduces contact recombination and resistance of the electron selective contact capped with an aluminum or silver electrode. Our results indicate that not only the metal in direct contact with the dielectric, but also the second capping metal is a crucial element of the contact stack. Although the exact mechanism is still unclear, low-work-function metals appear to perform better. We then apply the contact stack devised with these novel insights (1.5 nm MgFx/20 nm Mg/100 nm Al) and MoOx as well to dopant-free multilayer back contact (MLBC) solar cells to achieve an efficiency of 22.1% with an aperture area of 4.5 cm 2 by the directional evaporation for the patterning.
New Metallization Scheme for Interdigitated back Contact Silicon Heterojunction Solar Cells
Energy Procedia, 2013
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 (5x5cm²). Moreover, this technology can be used to increase the number of busbars on large area solar cells and therefore reduce series resistance effects.
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.
Solar
We present our own Interdigitated Back Contact (IBC) technology, which was developed at ISC Konstanz and implemented in mass production with and at SPIC Solar in Xining, China, with production efficiencies of over 24%. To our knowledge, this is the highest efficiency achieved in the mass production of crystalline silicon solar cells without the use of charge-carrier-selective contacts. With an adapted screen-printing sequence, it is possible to achieve open-circuit voltages of over 700 mV. Advanced module technology has been developed for the IBC interconnection, which is ultimately simpler than for conventional double-sided contacted solar cells. In the next step, we will realize low-cost charge-carrier-selective contacts for both polarities in a simple sequence using processes developed and patented at ISC Konstanz. With the industrialisation of this process, it will be possible to achieve efficiencies well above 25% at low cost. We will show that with the replacement of silver sc...
World Conference on Photovoltaic Energy Conversion, 2012
At imec a small area (4 cm 2) baseline process for interdigitated back contact (IBC) silicon solar cells based on n-type float-zone (FZ) and Czochralski (CZ) wafers has been developed. We obtained best cell conversion efficiencies of 23.3 % and 22.8 % on n-type 100 mm FZ and 125 mm CZ silicon substrates, respectively. Performing an identical process on one particular set of 156 mm n-type CZ substrates resulted in a large distribution of cell efficiencies within one wafer, likely to be related to the formation of oxygen precipitates during the high temperature process steps leading to degradation of the bulk lifetime. Further investigation will be done to make the process more tolerant to be applied on a variety of CZ substrates with different oxygen concentration. This IBC baseline serves as a test vehicle to innovate the integration sequence and is a starting point to upscale the IBC process to large-area IBC cells and explore new finger grid designs on 156 mm CZ silicon wafers. The final goal is to realize a simplified and cost effective IBC process flow reaching cell efficiencies above 22%.
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.
Thin Solid Films, 2006
We investigate the impacts of achieving buried grid metallic contacts (BGMC), with and without application of a front porous silicon (PS) layer, on the photovoltaic properties of polycrystalline silicon (pc-Si) solar cells. A grooving method based on Chemical Vapor Etching (CVE) was used to perform buried grid contacts on the emitter of pc-Si solar cells. After realizing the n + /p junction using a phosphorus diffusion source, BGMCs were realized using the screen printing technique. We found that the buried metallic contacts improve the short circuit current from 16 mA/cm 2 (for reference cell without buried contacts) to about 19 mA/cm 2 . After application of a front PS layer on the n + emitter, we observe an enhancement of the short circuit current from 19 to 24 mA/cm 2 with a decrease of the reflectivity by about 40% of its initial value. The dark I -V characteristics of the pc-Si cells with PS-based emitter show an important reduction of the reverse current together with an improvement of the rectifying behaviour. Spectral response measurements performed at a wavelength range of 400 -1100 nm showed a significant increase in the quantum efficiency, particularly at shorter wavelength (400 -650 nm). These results indicate that the BGMCs improve the carrier collection and that the PS layer acts as an antireflective coating that reduces reflection losses and passivates the front surface. This low cost and simple technology based on the CVE technique could enable preparing efficient polycrystalline silicon solar cells.