In the scope of solar cell characterisation, spatially resolved imaging (SRI) methods (EL, PL and LBIC) have long been a standard procedure for valuable in-depth evaluation and extraction of various ...spatially resolved material properties, especially those related to the electrical behaviour. While this extraction can be straightforward in the case of laterally homogeneous devices, the situation is vastly different when the structural features are laterally varying, such as in the case of interdigitated back contact (IBC) solar cells. We show that in the case of laterally varying devices inherent device optical properties play a far more important role in determining the measured profile in this case and may indeed overshadow any underlying electrical effects. We therefore propose and validate a methodology that couples SRI characterisation with advanced bottom-up simulation of IBC solar cells. The method fully accounts for lateral device variability and allows for accurate extraction of the underlying electrical phenomena. We demonstrate the applicability of the method on state-of-the-art high-efficiency IBC solar cells, and explain the key factors, which could lead to misinterpretation of the results obtained solely by SRI measurements.
•Interpretation of measured IBC electroluminescence profiles through opto-electrical simulation.•Decoupling of underlying optical and electrical phenomena.•Device optics overshadows recombination driven fluctuations of luminescence profiles.•Rear interface strongly influences the shape of the extracted luminescence profile.•Shape of the luminescence profile is highly dependent on imaging system’s aperture.
This work presents the upscaling of the tunnel IBC technology on large area, Czochralski (Cz) n-type wafers. At the junction level, a self-aligned PECVD masking technology has been developed for the ...deposition of hydrogenated nano-crystalline silicon (nc-Si:H) layers on industrial 6-inch pseudo-square wafers. This damage free patterning technology allows state-of-the-art passivation with a minority carrier lifetime of 9 ms at an injection level of 1015 cm-3, thus enabling extremely long diffusion lengths up to several millimetres. The use of indium-free, cost effective aluminium-doped zinc oxide strongly reduces the materials bill of the tunnel-IBC technology while maintaining very low contact resistance for both the electron and the hole contacts. Remarkably, these tunnel-IBC devices demonstrated a conversion efficiency of 25% on large area (90.25 cm2) industrial wafer with a thickness of 155 μm. Series resistance analysis points out probable losses from the hole contact and the base. The limitation of the Transfer Length Method is discussed when used to extract the hole contact resistance.
Interdigitated back contact (IBC) architecture can yield among the highest silicon wafer‐based solar cell conversion efficiencies. Since both polarities are realized on the rear side, there is a ...definite need for a patterning step. Some of the common patterning techniques involve photolithography, inkjet patterning, and laser ablation. This work introduces a novel patterning technique for structuring the rear side of IBC solar cells using the enhanced oxidation characteristics under the locally laser‐doped n++ back surface field (BSF) regions with high‐phosphorous surface concentrations. Phosphosilicate glass layers deposited via POCl3 diffusion serve as a precursor layer for the formation of local heavily laser‐doped n++ BSF regions. The laser‐doped n++ BSF regions exhibit a 2.6‐fold increase in oxide thickness compared to the nonlaser‐doped n+ BSF regions after undergoing high‐temperature wet thermal oxidation. The utilization of oxide thickness selectivity under laser‐doped and nonlaser‐doped regions serves two purposes in the context of the IBC solar cell, first patterning rear side and second acting as a masking layer for the subsequent boron diffusion. Proof‐of‐concept solar cells are fabricated using this novel patterning technique with a mean conversion efficiency of 20.41%.
An industrially viable novel patterning technique for fabrication of interdigitated back contact solar cells using the enhanced oxidation characteristics under laser‐doped back surface field regions is studied. The utilization of oxide thickness selectivity under laser‐doped and nonlaser‐doped regions serves two purposes, first patterning rear side and second acting as a masking layer for the subsequent boron diffusion.
Potential-induced degradation (PID) is characterized by the power loss of solar modules under high voltage stress across the module layer stack between framing/glass surface and solar cells. Standard ...silicon solar cells with a front side emitter may suffer from PID through massive shunting (PID-s) under high voltage stress conditions. PID was also reported in the past for cell concepts with a local emitter at the back side. For this case the underlying physical mechanism is not fully understood.
In this contribution the PID effect is investigated for interdigitated back contact solar cells (IBC cells). Parts of the front side of the cells are exposed to high-voltage stress using a recently developed cell test setup at variable temperature, voltage and polarity. Cells are investigated by means of electroluminescence (EL), IR-thermography, illuminated and dark I-V measurements before as well as after PID tests. Cell fragments are investigated after PID stressing using the electron beam induced current (EBIC) method in combination with scanning electron microscopy (SEM).
PID tests with a positive voltage respect to the grounded cell cause a locally degraded EL signal in the region where the PID stress was applied. In contrast, PID tests with the opposite polarity do not affect the EL behavior at all. I-V curves and thermography images indicate that PID stress does not significantly increase Rshunt. The local decrease of the EL intensity indicates increased non-radiative recombination. SEM/EBIC reveals neither local shunts nor distinct local degradation of the EBIC signal that could be attributed to PID tests with positive voltage.
The results indicate a degradation process related to a degradation of the front side passivation layer (PID-p), in contrast to the well-known PID-s effect. Based on the results a model concept for PID-p of IBC solar cells is proposed. Accordingly, the potential impact on the module power output under the influence of high voltage stress is assessed.
Silicon interdigitated back contact (IBC) solar cells with front floating emitter (FFE‐IBC) put forward a new carrier transport concept of “pumping effect” for minority carriers compared with ...traditional IBC solar cells with front surface field (FSF‐IBC). Herein, high‐performance FFE‐IBC solar cells are achieved theoretically combining superior crystalline silicon quality, front surface passivation, and shallow groove structure using 2D device model. The improvement of minority carrier transport capacity is realized in the conductive FFE layer through optimizing the doping concentration and junction depth. It is shown that the shallow groove on the rear side of FFE‐IBC solar cells can effectively enhance the carrier collection ability by means of minimizing the negative impact of undiffused gap or surface p–n junction. The high efficiency exceeding 25% can be realized on silicon FFE‐IBC solar cells with the novel cell structure and optimized cell parameters, where the back surface field and emitter region width can be made for the same with only a slight sacrifice of photocurrent density and conversion efficiency. It is demonstrated theoretically that the realization of high‐efficiency and low‐cost silicon IBC solar cells is feasible due to the increase of the module fabrication tolerance.
Minority‐carrier transport and collection capacity can be improved, respectively, by the front conductive front floating emitter (FFE) layer and rear shallow groove. Conversion efficiency over 25% on interdigitated back contact silicon solar cells with FFE is achieved, where the back surface field and emitter region width can be made for the same with only a slight sacrifice of photocurrent.
In this study, zinc oxide (ZnO) nanostructures were grown on interdigitated back contact silicon solar cells (IBC-SSCs) by using the microwave-assisted hydrothermal method. The effect of these ZnO ...nanostructures grown by different precursor concentrations on the conversion efficiency of solar cells was investigated. The as-prepared ZnO products were analyzed by XRD, SEM, EDS, UV-vis, and PL, then were grown onto IBC-SSCs. The IBC-SSCs conversion efficiency without any ZnO nanostructure was 8.88%, and with a ZnO nanostructure, it reached 12.15%. which effectively enhances the conversion efficiency of IBC-SSCs.
Interdigitated back contact (IBC) solar cells have great potential for high efficiency because of their unique structure. IBC solar cells demand for high quality of front surface passivation. In this ...work, 2D numerical simulations have been done to investigate the potential of front surface field (FSF) offered by stack of n-type doped and intrinsic amorphous silicon (a-Si) layers on the front surface of IBC solar cells. Simulations results clearly indicate that the electric field of FSF should be strong enough to repel minority carries and cumulate major carriers near the front surface. However over-strong electric field tends to drive electrons into a-Si layer leading to severe recombination loss. The n-type doped amorphous silicon (n-a-Si) layer has been optimized in terms of doping level and thickness. The optimized intrinsic amorphous silicon (i-a-Si) layer should be as thin as possible with an energy band gap (Eg) larger than 1.4 eV. In addition, the simulations concerning interface defects strongly suggest that FSF is an essential part when the front surface is not passivated perfectly. Without FSF, the IBC solar cells become more sensitive to interface defect density.
•We propose the application of stack of amorphous silicon layers as front surface field for diffused IBC solar cells.•We optimized the amorphous silicon layers in terms of doping level, thickness, bandgap and interface defects density.•Heterojunction structure is integrated on the front surface of IBC solar cells and energy band diagrams are analyzed.
Ion implantation and laser processing technologies are very attractive for the fabrication of industrially feasible interdigitated back-contact (IBC) solar cells. In this work, p+ emitters were ...fabricated by boron implantation and laser annealing, and the electrical properties of emitters were investigated. An emitter sheet resistance (Rsh) in the range of 30-200Ω/□ could be achieved by varying the implanted dose. The saturation current density (Joe) of the passivated p+ emitter with Rsh of ∼125Ω/□ reached 95 fA/cm2, and the contact resistivity was determined to be as low as 5×10-6Ω·cm2. Such localized p+ emitters can be applied to n-type IBC solar cells, which could avoid the high temperature thermal annealing step and related problems.
Back-contact amorphous-silicon (a-Si) /crystallinesilicon (c-Si) heterojunction appears the best structure to realize solar cells with the world top-class efficiency. However, the fabrication cost is ...a draw-back due to complicated patterning process for making nand pback-electrodes. To overcome it, we attempted to make n-a-Si islands in p-a-Si layers by plasma ionimplantation of phosphorus (P) atoms. We discovered that high temperature annealing was not necessary after plasma ionimplantation, contrary to ion implantation into c-Si, and we succeeded to convert p-type a-Si (p-a-Si)/intrinsic a-Si (i-a-Si)/c-Si hetero-structure to n-type a-Si (n-a-Si)/i-a-Si/c-Si without degradation of carrier lifetimes or heterojunction quality.
In this paper we show the results of the cost model developed in LIMA project (Seventh Framework Programme, CN: 248909). The LIMA project is entitled “Improve photovoltaic efficiency by applying ...novel effects at the limits of light to matter interaction”. The project started in January 2010 and during this year a cost model of the device developed in the project has been developed to assess the industrial viability of this innovative approach to increase the efficiency and reduce the cost of photovoltaic solar cells. During 2011 the cost model has been actualized and a new scenario has been defined. The LIMA project exploits cutting edge photonic technologies to enhance silicon solar cell efficiencies with new concepts in nanostructured materials. It proposes nanostructured surface layers designed to increase the light absorption in the solar cell while decreasing the surface and interface recombination loss. The integration on a back contact solar cell further reduces these interface losses and avoids shading. The project improves light-matter interaction by the use a surface plasmonic nanoparticle layer. This reduces reflection and efficiently couples incident radiation into the solar cell where it is trapped by internal reflection. Surface and interface recombination are minimized by using silicon quantum dot superlattices in a passivating matrix.
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