New Metallization Scheme for Interdigitated back Contact Silicon Heterojunction Solar Cells (original) (raw)
Related papers
Improvement of Back Surface Metallization in a Silicon Interdigitated back Contacts Solar Cell
Energy Procedia, 2013
The rear metallization is an important element in order to improve the efficiency yield. Depending on the structure of the metal stack used to contact the doped areas, the reflectivity of this back reflector is considerably changed. In the literature, the metal stacks used to contact the cell are rather complex (Si/Al/Ti/Pd/Ag) in order to obtain a low contact resistivity for the n-doped and p-doped zones, a good mechanical bond and a good back surface reflectivity. We proposed in this paper, a simpler Si/Ti/Ag stack which does not need any annealing and provides electrical contacts able to improve the efficiency of an IBC (Interdigitated Back Contacts) solar cell.
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.
Numerical simulation of interdigitated back contact hetero-junction solar cells
2013
The goal of this thesis is the application of an opto-electronic numerical simulation to heterojunction silicon solar cells featuring an all back contact architecture (Interdigitated Back Contact Hetero-Junction IBC-HJ). The studied structure exhibits both metal contacts, emitter and base, at the back surface of the cell with the objective to reduce the optical losses due to the shadowing by front contact of conventional photovoltaic devices. Overall, IBC-HJ are promising low-cost alternatives to monocrystalline wafer-based solar cells featuring front and back contact schemes, in fact, for IBC-HJ the high concentration doping diffusions are replaced by low-temperature deposition processes of thin amorphous silicon layers. Furthermore, another advantage of IBC solar cells with reference to conventional architectures is the possibility to enable a low-cost assembling of photovoltaic modules, being all contacts on the same side. A preliminary extensive literature survey has been helpfu...
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%.
Simplification for High Efficiency , Small Area Interdigitated Back Contact Silicon Solar Cells
2013
A baseline process for small area (4 cm) interdigitated back contact (IBC) silicon solar cells at imec is presented, based on n-type 156x156 mm CZ silicon wafers. This process has been stabilised, and best obtained (calibrated) conversion efficiencies of 23.1% (average 22.8%) have been achieved. Recent developments have focused on process simplification, and are the subject of this report. The key findings include the benefits of introducing a wet oxidation step as the boron activation/emitter-passivation step (higher sheet resistance, lower J0, and consequently higher efficiency). The surface cleaning routines have also been revised, resulting in slight increases in efficiency for simplified cleaning process (with consequent reduced process time/chemical consumption). Finally, results on contact definition by laser ablation are presented, showing a strong impact of the contact grid density on the BSF and emitter regions, on cell performance. The maximum achieved efficiency of 22.9%...
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...
Two-Dimensional Simulations of Interdigitated Back Contact Silicon Heterojunctions Solar Cells
Engineering Materials, 2012
Interdigitated back contact silicon heterojunction (IBC-SiHJ) solar cells that combine the amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction-and interdigitated back contact (IBC) concepts are very promising in order to reach the highest one-junction efficiencies. In this chapter, a comparative twodimensional simulation study has been done on the IBC-SiHJ structure based on n-type and p-type crystalline silicon by varying the values of the following parameters: minority carrier lifetime in c-Si, c-Si thickness, c-Si doping concentration, surface recombination velocity, density of defect states at the a-Si:H/c-Si heterointerface and rear side geometry. The influence of these parameters has been tested by generating the current-voltage characteristics under illumination. Results indicate that the key parameters to achieve high efficiency are high c-Si substrate quality, low surface recombination velocity especially at the front surface, and a low recombining a-Si:H/c-Si interface. The width of the gap region (spacing between the back-surface field (BSF) and the emitter) must be kept as small as possible to avoid recombination of minority carriers in the bulk c-Si. For IBC-SiHJ based on n-type c-Si, the optimum geometry corresponds to a minimum size BSF region and a maximum size emitter region while for IBC-SiHJ based on p-type c-Si a BSF width equivalent to around 30% of the pitch is an optimum.
Progress in Photovoltaics: Research and Applications, 1994
The influence of the point spacing and size on the cell eficiency is studied for direrent silicon solar cell structures with local rear contacts: the PERC (passivated emitter and rear cell) with its high recombination at the rear contacts and the LBSF (local back surjace field) or PERL (passivated emitter and rear locally diflused) cell with reduced combination at the rear contacts due to a diflused high-low junction (or LBSF) beneath the contacts. Float zone materials of diflerent resistivities have been investigated. The experimental results are explained by three-dimensional finite difference simulations for the open-circuit voltage, the short-circuit current and the fill factor.
Analysis of a-Si:H/TCO contact resistance for the Si heterojunction back-contact solar cell
Solar Energy Materials and Solar Cells, 2014
The contact resistance of amorphous Si (a-Si:H)/transparent-conducting oxide (TCO) is evaluated and analyzed in terms of the contribution to the series resistance (R s) and fill factor (FF) in the Si heterojunction back-contact (HBC) solar cell. It is shown that p-a-Si:H (emitter) and n-a-Si:H (back surface field: BSF)/TCO contact resistance are of similar values (0.37-38 Ω cm 2) which are much higher than those of doped crystalline Si/metal contacts used in conventional Si solar cells. Of some factors affecting R s loss in the HBC solar cell, BSF/TCO contact is the most significant one when considering the contact area. By interleaving the n-type microcrystalline Si (n-μc-Si) between n-a-Si:H and TCO, 6-inch HBC solar cell with 20.5% efficiency is obtained, which was attributed to the reduced R s and improved FF. It is noteworthy that the variations of R s and FF are well estimated by measuring BSF-contact resistance, and are close to the empirical data: reduction in R s to 1.77 Ω cm 2 and the increase in FF by 6.0% compared to the cell without n-μc-Si interface layer. The results indicate that there is much room for higher efficiency by reducing the emitter-and BSF-contact resistance. Nonetheless, the method developed here can be a powerful tool to analyze the resistance component in HBC cell.
Simulation Results: Optimization of Contact Ratio for Interdigitated Back-Contact Solar Cells
International Journal of Photoenergy, 2017
In the fabrication of interdigitated back contact (IBC) solar cells, it is very important to choose the right size of contact to achieve the maximum efficiency. Line contacts and point contacts are the two possibilities, which are being chosen for IBC structure. It is expected that the point contacts would give better results because of the reduced recombination rate. In this work, we are simulating the effect of contact size on the performance of IBC solar cells. Simulations were done in three dimension using Quokka, which numerically solves the charge carrier transport. Our simulation results show that around 10% of contact ratio is able to achieve optimum cell efficiency.