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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The n-type silicon integrated-back contact (IBC) solar cell has attracted much attention due to its high efficiency, whereas its performance is very sensitive to the wafer of low quality or the ...contamination during high temperature fabrication processing, which leads to low bulk lifetime τbulk. In order to clarify the influence of bulk lifetime on cell characteristics, two-dimensional (2D) TCAD simulation, combined with our experimental data, is used to simulate the cell performances, with the wafer thickness scaled down under various τbulk conditions. The modeling results show that for the IBC solar cell with high τbulk, (such as 1 ms-2 ms), its open-circuit voltage Voc almost remains unchanged, and the short-circuit current density Jsc monotonically decreases as the wafer thickness scales down. In comparison, for the solar cell with low τbulk (for instance, < 500 μs) wafer or the wafer contaminated during device processing, the Voc increases monotonically but the Jsc first increases to a maximum value and then drops off as the wafer's thickness decreases. A model combing the light absorption and the minority carrier diffusion is used to explain this phenomenon. The research results show that for the wafer with thinner thickness and high bulk lifetime, the good light trapping technology must be developed to offset the decrease in Jsc.
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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The n-type silicon integrated-back contact(IBC) solar cell has attracted much attention due to its high efficiency,whereas its performance is very sensitive to the wafer of low quality or the ...contamination during high temperature fabrication processing, which leads to low bulk lifetime τbulk. In order to clarify the influence of bulk lifetime on cell characteristics, two-dimensional(2D) TCAD simulation, combined with our experimental data, is used to simulate the cell performances, with the wafer thickness scaled down under various τbulk conditions. The modeling results show that for the IBC solar cell with high τbulk,(such as 1 ms-2 ms), its open-circuit voltage V oc almost remains unchanged, and the short-circuit current density J sc monotonically decreases as the wafer thickness scales down. In comparison, for the solar cell with low τbulk(for instance, 〈 500 μs) wafer or the wafer contaminated during device processing, the V oc increases monotonically but the J sc first increases to a maximum value and then drops off as the wafer's thickness decreases. A model combing the light absorption and the minority carrier diffusion is used to explain this phenomenon. The research results show that for the wafer with thinner thickness and high bulk lifetime, the good light trapping technology must be developed to offset the decrease in J sc.