Interdigitated Cells Research Articles

Study on Performance Stability Improvement of Polymer Electrolyte Fuel Cells with Interdigitated Gas Flow Channels on a Gas Diffusion Layer

Recently, a new concept was developed for the design of polymer electrolyte fuel cells, combined a flat separator and a porous gas diffusion layer (GDL) with interdigitated gas-flow channels.1 This new design cell has demonstrated higher performances than that of a conventional cell combined a solid separator with serpentine flow-channels and a flat GDL.2 Conventional interdigitated flow-channel designs, which consist of a solid separator with interdigitated gas-flow channels and a flat GDL, have been known for their higher efficiency of the oxygen supply to the catalyst layer, in comparison with serpentine or parallel flow-channels in combination with a flat GDL, because of the forced convection of the supplied gas in the GDL. However, conventional interdigitated flow-channels have faced two issues associated with low performance: one occurs under high-humidity conditions because of nonuniform gas flow due to accumulated water in the GDL; the other is caused by forced water discharge from the GDL under low-humidity conditions.In this study, to investigate the possibility of the new cell design to overcome such performance issues of conventional interdigitated cells, both conventional and new cell designs were tested with single cells of 1 cm2 active area, and the performances were compared at high and low humidity with various conditions of gas supply. From these results, we have found that the new design of the GDL with interdigitated channels has a clear advantage over that of the conventional separator with interdigitated channels, being able to maintain higher performance under conditions of both water excess and water shortage.3 To reveal the mechanism of the improvement in the cell performance, the temperature and gas flow distributions in the GDL of the new and the conventional interdigitated cells were calculated by numerical simulation, and the water distribution was visualized by X-ray imaging.4 From comparisons of these experimental and numerical results in the two cells, the porous ribs in the newly designed cell were found to play several important roles, as follows: under conditions of excess water, the porous ribs with relatively low thermal conductivity help to alleviate water accumulation in the GDL by acting as a reservoir for excess water and also by increasing the temperature in the GDL adjacent to the catalyst layer; and, under conditions of water shortage, the porous ribs help to alleviate the dry-out of the GDL by withdrawing water from the reservoir shortly and also by decreasing the rate of gas flow forced through the GDL because the porous ribs act as the short-cut pathway for the gas flow.Based on these mechanistic and performance analyses, it is becoming clearer that the new cell design, with interdigitated flow-channels and porous ribs, has the potential to overcome the performance issues of conventional interdigitated cells. Acknowledgement This work was partially based on results obtained from project JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References Watanabe et al., J. Electrochem. Soc., 166, F3210 (2019).Nasu et al., J. Power Sources, 530, 231251 (2022).Inoue et al., J. Electrochem. Soc., 169, 114504 (2022).Inoue et al., J. Power Sources, 585, 233623 (2023). Figure 1

HDA6 modulates Arabidopsis pavement cell morphogenesis through epigenetic suppression of ROP6 GTPase expression and signaling.

The transcriptional regulation of Rho-related GTPase from plants (ROPs), which determine cell polarity formation and maintenance during plant development, still remains enigmatic. In this study, we elucidated the epigenetic mechanism of histone deacetylase HDA6 in transcriptional repression of ROP6 and its impact on cell polarity and morphogenesis in Arabidopsis leaf epidermal pavement cells (PCs). We found that the hda6 mutant axe1-4 exhibited impaired jigsaw-shaped PCs and convoluted leaves. This correlated with disruptions in the spatial organizations of cortical microtubules and filamentous actin, which is integral to PC indentation and lobe formation. Further transcriptional analyses and chromatin immunoprecipitation assay revealed that HDA6 specifically represses ROP6 expression through histone H3K9K14 deacetylation. Importantly, overexpression of dominant negative-rop6 in axe1-4 restored interdigitated cell morphology. Our study unveils HDA6 as a key regulator in Arabidopsis PC morphogenesis through epigenetic suppression of ROP6. It reveals the pivotal role of HDA6 in the transcriptional regulation of ROP6 and provides compelling evidence for the functional interplay between histone deacetylation and ROP6-mediated cytoskeletal arrangement in the development of interdigitated PCs.

Design Rule of Electron- and Hole-Selective Contacts for Polycrystalline Silicon-Based Passivating Contact Solar Cells.

A crystalline silicon (c-Si) solar cell with a polycrystalline silicon/SiOx (poly-Si/SiOx) structure, incorporating both electron and hole contacts, is an attractive choice for achieving ideal carrier selectivity and serving as a fundamental component in high-efficiency perovskite/Si tandem and interdigitated back-contact solar cells. However, our understanding of the carrier transport mechanism of hole contacts remains limited owing to insufficient studies dedicated to its investigation. There is also a lack of comparative studies on the poly-Si/SiOx electron and hole contacts for ideal carrier-selective solar cells. Therefore, this study aims to address these knowledge gaps by exploring the relationship among microstructural evolution, dopant in-diffusion, and the resulting carrier transport mechanism in both the electron and hole contacts of poly-Si/SiOx solar cells. Electron (n+ poly-Si/SiOx/substrate)- and hole (p+ poly-Si/SiOx/substrate)-selective passivating contacts are subjected to thermal annealing. Changes in the passivation properties and carrier transport mechanisms of these contacts are investigated during thermal annealing at various temperatures. Notably, the results demonstrate that the passivation properties and carrier transport mechanisms are strongly influenced by the microstructural evolution of the poly-Si/SiOx layer stack and dopant in-diffusion. Furthermore, electron and hole contacts exhibit common behaviors regarding microstructural evolution and dopant in-diffusion. However, the hole contacts exhibit relatively inferior electrical properties overall, mainly because both the SiOx interface and the p+ poly-Si are found to be highly defective. Moreover, boron in the hole contacts diffuses deeper than phosphorus in the electron contacts, resulting in deteriorated carrier collection. The experimental results are also supported by device simulation. Based on these findings, design rules are suggested for both electron and hole contacts, such as using thicker SiOx and/or annealing the solar cell at a temperature not exceeding the critical annealing temperature of the hole contacts.

Scale-up of Interdigitated Design from Small Cell to Large Cell for Aqueous Redox Flow Batteries

Redox flow batteries present attributes for large-scale energy storage. Interdigitated flow configuration is a promising structure due to its higher power density and lower pressure loss. The screening for new electrolyte is usually first tested on small cell (<10 cm2) due to its easy operation and less electrolyte consumption. To test the electrolyte functionality in practical application condition, large-scale (i.e., 780 cm2) testing is required conventionally in laboratory or industry. The twice testing is due to the fact that the testing results in small cell are different from that for large-scale interdigitated cell. In order to reduce the testing cycles and quickly estimate the application of new electrolytes, scale-up of interdigitated design from small cell to large cell is investigated in this work.Numerical simulation on different scales of interdigitated cells (10cm2, 78cm2, 130cm2, 780cm2) is conducted to assess the polarization. The local velocity distribution and redox-active species concentration are extracted to show their dominance on the cell performance. It is shown that with similar velocity and concentration distribution, cell with different scales present similar limiting current density and power density, regardless of active area. It implies that the results in small cells can be directly scaled up for large cells without further testing. It provides an avenue for quick estimation of new electrolyte in application condition.Experimental testing is conducted on vanadium redox flow battery for different scale of interdigitated cell. The experimental results will demonstrate this scale-up from small-scale to middle-scale interdigitated cell.

Geometric and network organization of visceral organ epithelium.

Mammalian epithelia form a continuous sheet of cells that line the surface of visceral organs. To analyze the epithelial organization of the heart, lung, liver and bowel, epithelial cells were labeled in situ, isolated as a single layer and imaged as large epithelial digitally combine montages. The stitched epithelial images were analyzed for geometric and network organization. Geometric analysis demonstrated a similar polygon distribution in all organs with the greatest variability in the heart epithelia. Notably, the normal liver and inflated lung demonstrated the largest average cell surface area (p < 0.01). In lung epithelia, characteristic wavy or interdigitated cell boundaries were observed. The prevalence of interdigitations increased with lung inflation. To complement the geometric analyses, the epithelia were converted into a network of cell-to-cell contacts. Using the open-source software EpiGraph, subgraph (graphlet) frequencies were used to characterize epithelial organization and compare to mathematical (Epi-Hexagon), random (Epi-Random) and natural (Epi-Voronoi5) patterns. As expected, the patterns of the lung epithelia were independent of lung volume. In contrast, liver epithelia demonstrated a pattern distinct from lung, heart and bowel epithelia (p < 0.05). We conclude that geometric and network analyses can be useful tools in characterizing fundamental differences in mammalian tissue topology and epithelial organization.

Mitigation of shunt in poly-Si/SiO passivated interdigitated back contact monocrystalline Si solar cells by self-aligned etching between doped fingers

Mitigation of shunt in poly-Si/SiO passivated interdigitated back contact monocrystalline Si solar cells by self-aligned etching between doped fingers

A Spot-Area Method to Evaluate the Incidence Angle Modifier of Photovoltaic Devices—Part 1: Cells

The angle of incidence of solar irradiation on photovoltaic modules varies throughout the day. At larger angles of incidence, the modules are subject to higher reflection losses, resulting in lower light transmission and energy yield. The impact of the relative angular transmittance on the energy yield is often evaluated with a correction factor, commonly referred to as incidence angle modifier (IAM). In this article, a new method to quantify the IAM of photovoltaic devices is presented, which is different from the methods proposed in IEC 61853-2: It encompasses a spot-area irradiation, a customized angle probe holder, and a current-to-voltage converter. This first part focuses on single-cell minimodules and validates the new method on two different cell architectures—an interdigitated back-contact solar cell and a four-busbar solar cell, with an analysis of the measurement bias due to busbars. A second part will follow on the implementation of the same method to commercial-size silicon modules. The study is intended to contribute to the IEC 61853-2 standard. A detailed uncertainty analysis is presented and the method is validated versus IEC 61853-2. Our proposed method shows great potential as it is less expensive and more adaptable than existing standard methods.

Photovoltaics literature survey (no. 182)

Photovoltaics literature survey (no. 182)

Mitigating Cut Losses in Interdigitated Back Contact Solar Cells

The edge recombination losses of crystalline silicon solar cells become significant when they are cut into smaller pieces to be assembled into modules. With the interdigitated pattern of doped <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$p$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$n$</tex-math></inline-formula> regions on the rear side, the interdigitated back contact (IBC) solar cells can be cut through different doped regions. In this study, the cutting losses in IBC solar cells are investigated and various cutting scenarios are studied. Through simulations and experimental measurements, it is found that the cut losses can be reduced by cutting through the back surface field rather than through the emitter. The losses under low light intensity are reduced to an even greater extent. When a 23% cell is cut into 1/3 pieces, the efficiency can be increased by 1.2% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\mathrm{rel}$</tex-math></inline-formula> (cut related losses were improved from 2.0% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\mathrm{rel}$</tex-math></inline-formula> to 0.8% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\mathrm{rel}$</tex-math></inline-formula> ) under standard 1-sun testing conditions, compared to cutting through the emitter. Under low light intensity of 0.25 sun, the improvement is around 2.4% <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_\mathrm{rel}$</tex-math></inline-formula> . The improvement is mainly due to lower FF losses in the I–V characteristics, and this is further confirmed by Suns– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$V_{\text{oc}}$</tex-math></inline-formula> and PL measurements. In the pFF analysis, the additional losses due to laser damage are also observed. This strategy of cutting through the BSF region in IBC solar cells can be quickly adopted in mass production without the need for additional processes or equipment and both module power and energy yield can be increased.

Improvement of PEFC Performance Stability under High and Low Humidification Conditions by Use of a Gas Diffusion Layer with Interdigitated Gas Flow Channels

A new design concept for polymer electrolyte fuel cells, which included a flat-metal separator and a gas diffusion layer (GDL) with interdigitated gas flow channels (FCs), was developed in our previous research. This design led to improved performance compared to that obtained with the conventional design of a metal separator with FCs and a flat GDL. Applications of the interdigitated gas flow channels formed on the separator, however, have conventionally faced two issues associated with low performance: one occurs under high humidity conditions because of nonuniform gas flow due to accumulated water in the GDL; the other is caused by forced water discharge from the GDL under low humidity conditions. In this study, both conventional and new cell designs are tested with single cells of 1 cm2 active area, and the performances are compared at high and low humidity with various conditions of gas supply. From these results, we have found that the new design of the GDL with interdigitated channels has a clear advantage over the conventional interdigitated cell in being able to maintain high performance under conditions of both water excess and water shortage.

Performance Enhancement of Interdigitated Heterojunction Solar Cells with Discotic Molecule

Ordered interdigitated heterojunction as a promising nanostructure has attracted considerable attention due to its potential application in solar cells. However, a suitable construction to achieve effective free carrier transport in these nanostructures remains a challenge. In this study, interdigitated nanostructure was fabricated by combining vertically orientated TiO2 nanotube array with discotic liquid crystal Copper (II) 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (tbCuPc). These discotic molecules were assembled as homeotropic alignment in the interdigitated nanostructure, which enhanced the carrier mobility of active layer considerably. The performance of photovoltaic cells with this interdigitated heterojunction was improved. Molecule orientation leading to charge carrier mobility enhancement was found to play a key role in improving the power conversion efficiency of the devices substantially.

Imaging Current Paths in Silicon Photovoltaic Devices with a Quantum Diamond Microscope

Magnetic imaging with nitrogen-vacancy centers in diamond, also known as quantum diamond microscopy, has emerged as a useful technique for the spatial mapping of charge currents in solid-state devices. In this work, we investigate an application to photovoltaic (PV) devices, where the currents are induced by light. We develop a widefield nitrogen-vacancy microscope that allows independent stimulus and measurement of the PV device, and test our system on a range of prototype crystalline silicon PV devices. We first demonstrate micrometer-scale vector magnetic field imaging of custom PV devices illuminated by a focused laser spot, revealing the internal current paths in both short-circuit and open-circuit conditions. We then demonstrate time-resolved imaging of photocurrents in an interdigitated back-contact solar cell, detecting current build-up and subsequent decay near the illumination point with microsecond resolution. This work presents a versatile and accessible analysis platform that may find distinct application in research on emerging PV technologies.

Performance Investigation of a Proposed Flipped npn Microstructure Silicon Solar Cell Using TCAD Simulation

This work aims at inspecting the device operation and performance of a novel flipped npn microstructure solar cell based on low-cost heavily doped silicon wafers. The flipped structure was designed to eliminate the shadowing effect as applied in the conventional silicon-based interdigitated back-contact cell (IBC). Due to the disappearance of the shadowing impact, the optical performance and short-circuit current density of the structure have been improved. Accordingly, the cell power conversion efficiency (PCE) has been improved in comparison to the conventional npn solar cell microstructure. A detailed analysis of the flipped npn structure was carried out in which we performed TCAD simulations for the electrical and optical performance of the flipped cell. Additionally, a comparison between the presented flipped microstructure and the conventional npn solar cell was accomplished. The PCE of the conventional npn structure was found to be 14.5%, while it was about 15% for the flipped structure when using the same cell physical parameters. Furthermore, the surface recombination velocity and base bulk lifetime, which are the most important recombination parameters, were studied to investigate their influence on the flipped microstructure performance. An efficiency of up to 16% could be reached when some design parameters were properly fine-tuned. Moreover, the impact of the different physical models on the performance of the proposed cell was studied, and it was revealed that band gap narrowing effect was the most significant factor limiting the open-circuit voltage. All the simulations accomplished in this analysis were carried out using the SILVACO TCAD process and device simulators.

Interdigitated back-contacted crystalline silicon solar cells fully manufactured with atomic layer deposited selective contacts

The interdigitated back-contacted (IBC) solar cell concept has been extensively studied for single-junction cells and more recently as a good choice for three-terminal tandem devices. In this work, carrier-selective contacts based on transition metal oxides deposited by atomic layer deposition (ALD) technique are applied to IBC c-Si(n) devices. In the first part of the study, we develop a hole-selective contact based on thin ALD vanadium oxide (V2O5) layers without using an amorphous silicon interlayer. The ALD process has been optimised, i.e. number of ALD cycles and deposition temperature, as a trade-off between surface passivation and contact resistivity. Noticeable surface passivation with recombination current densities around 100 fA/cm2, as well as reasonable contact resistivity values below 250 mΩcm2 are reached using 200 ALD V2O5 cycles deposited at a deposition temperature of 125 °C (∼10 nm layer thickness). The optimised ALD V2O5-based contact is combined with both an ALD TiO2-based electron-selective contact and an excellent surface passivation in non-contacted regions provided by ALD Al2O3 films, to form a fully ALD IBC c-Si(n) solar cell scheme. Fabricated devices yield photovoltaic efficiencies and pseudo efficiencies, i.e. calculated without series resistance losses, of 18.6% and 21.1% respectively (3 cm × 3 cm device area). These results reveal the potential of the ALD technique to deposit transition metal oxide (TMO) films as selective contacts on high efficiency devices, paving the way of using low thermal-budget, low cost and highly scalable processes for a highly demanding IBC solar cell architecture in the photovoltaic industry.

Highly Stable Interdigitated PbS Quantum Dot and ZnO Nanowire Solar Cells with an Automatically Embedded Electron-Blocking Layer

We have constructed heterojunction iodide ligand PbS quantum dot (QD) and ZnO nanowire (NW) solar cells. In these interdigitated structures, PbS QDs are well-embedded within ZnO NWs grown on a dense ZnO layer. A Au back contact is directly formed on the iodide ligand PbS QD surface layer. In the widely studied colloidal QD-based heterojunction solar cells, the PbS QD active layer is sandwiched between the hole-blocking layer (or electron-accepting layer) and the electron-blocking layer (EBL) (or hole-transport layer). In contrast, our solar cells contain no EBL except an additional thin PbS QD capping layer, which was deposited on the interdigitated layer to ensure the complete infiltration of the PbS QDs, and prevent shortening between the ZnO NWs and Au back contact. The interdigitated layer was constructed using a layer-by-layer dip-coating method to achieve sufficient infiltration of PbS QDs in the ZnO NWs. Owing to highly efficient charge separation in the interdigitated structure, our cell achieved a high external quantum efficiency in the visible and infrared regions, despite using only iodide ligand PbS QDs. Using cross-sectional Kelvin probe force microscopy, we confirmed that the PbS QD capping layer formed between the ZnO NW and Au back contact intrinsically functioned as an EBL. Consequently, the solar cells with ZnO NWs and iodide ligand PbS QDs maintained their performance after 500 days of storage in air without encapsulation. This stability performance surpasses most of the previously reported solar cells with PbS QDs. An encapsulated 1.0 cm2 solar cell maintained its power output for over 75 h under continuous one-sun illumination with no significant degradation. The proposed solar cell architecture with an automatically embedded EBL can realize highly efficient and stable colloidal QD-based solar cells. Moreover, the interdigitated architecture concept can be extended to various organic and inorganic hybrid solar cells.

Low-Resistance Hole Contact Stacks for Interdigitated Rear-Contact Silicon Heterojunction Solar Cells

Achieving low contact resistivity for the p-contact in silicon heterojunction (SHJ) solar cells is challenging when classic n-type transparent conductive oxides (TCOs), such as indium tin oxide (ITO), are used in the contact stack. Here, we report on SHJ solar cells with interdigitated back-contact (IBC) and a direct aluminum (Al) metallization applied to the p-contact. We find that carefully annealing an Al/a-Si:H(p) (p-type amorphous silicon) contact at moderate temperatures leads to a specific contact resistivity that is half as low as its silver (Ag)/ITO counterpart. This is explained by Al diffusing into a-Si:H(p) upon temperature treatment, forming a partially crystallized aluminum silicide layer. For a sufficiently high doping level in a-Si:H(p), this enables an efficient tunnel-recombination of holes from a-Si:H(p) to the Al contact. An estimate for this tunneling-dominated specific contact resistivity is calculated as a function of the interface doping density. Best fabricated IBC SHJ solar cells with Al p-contact yield a fill factor of 77.5% and a power conversion efficiency of 22.3%. The main differences to devices with an Ag/ITO/a-Si:H(p) contact stack are a decrease in open-circuit voltage by 14 mV and a slightly higher series resistance ( R s). While the first aspect can be ascribed to increased interface recombination, the second one is unexpected and requires further investigation. Interestingly, omitting an intermediate TCO does not lead to current losses in devices with Al contacts, which is further investigated by optical simulations. Finally, electrical equivalent circuit simulations are conducted to describe the electrical behavior of the investigated devices.

Subcellular coordination of plant cell wall synthesis.

Organelles of the plant cell cooperate to synthesize and secrete a strong yet flexible polysaccharide-based extracellular matrix: the cell wall. Cell wall composition varies among plant species, across cell types within a plant, within different regions of a single cell wall, and in response to intrinsic or extrinsic signals. This diversity in cell wall makeup is underpinned by common cellular mechanisms for cell wall production. Cellulose synthase complexes function at the plasma membrane and deposit their product into the cell wall. Matrix polysaccharides are synthesized by a multitude of glycosyltransferases in hundreds of mobile Golgi stacks, and an extensive set of vesicle trafficking proteins govern secretion to the cell wall. In this review, we discuss the different subcellular locations at which cell wall synthesis occurs, review the molecular mechanisms that control cell wall biosynthesis, and examine how these are regulated in response to different perturbations to maintain cell wall homeostasis.

Laser Patterned Electroplated Copper Contacts for Interdigitated Back Contact Silicon Solar Cells

Metallization of interdigitated back contacts for Si-based solar cells (IBC), where both the n- and p-contacts are processed on the rear side of the device, currently requires costly and labor-intensive masking, photolithography, and/or screen printing approaches, which are difficult for scale-up to high-throughput high-volume manufacturing. Electrodeposition (ED) offers a low cost, scalable, and selective approach for IBC metallization, but is potentially complicated by the close geometry of the contacts and the need for simultaneous plating to both contacts to achieve high processing throughput. Direct laser patterning of a thin seed metal film offers a fast single-step process for defining contact areas, reducing both device handling and chemical use, and allows simple variation of contact design to implement external electrical connections for ED, as well as rapid testing of alternative pattern dimensions and the subsequent effects on device performance. A simple and flexible direct laser scribing approach for processing of IBCs through patterning of thin Ni seed layers prior to Cu electroplating will be presented.IBC patterns were laser-scribed on blanket evaporated Ni seed layers on a-SiNx:H-coated textured-Si wafers (Ni/a-SiNx:H/Si) prior to plating. Patterning was carried out at optimum laser powers to achieve electrical isolation of the Ni contacts. Pattern designs, with 12 mm long n- and p-fingers of 400 and 1200 µm in width, respectively, were fabricated to include tabs for external contacting for ED (Fig. 1a). Contact patterns were prepared using either double-pass-focused or single-pass-defocused laser conditions during ablation. Samples processed with either single (Fig. 1b) or double (Fig. 1c) laser passes show well-defined ~100 µm cuts, however, those patterned with the latter condition showed a ~20 µm laser-induced trench along the center of all scribe lines, due to overlap of the beam paths, and which was not observed for patterns processed with a single pass. Plating conditions from acidified CuSO4-based baths were optimized for deposit reproducibility, uniformity, and adhesion on substrates of non-patterned thin evaporated Ni seed layers on 150 µm textured-Si wafers. Films of growth rate ~0.1 µm/min were achieved, with contact resistance (RC) ~5 mΩ.cm2, and excellent adhesion, enduring pull tests of >5 N where the Si wafer broke before any peeling of the Cu layer.With plating to laser-patterned IBC substrates, significant Cu features grow from the edges of the laser cuts (Fig. 1d), eventually shorting the fingers and leading to unwanted deposition outside of the contact areas. Shorting was not observed with plating to IBC Ni seed patterns that had been evaporated through a shadow mask, suggesting residual conductive phases in the scribes are responsible for the growth of the shorts. Brief chemical etches were carried out after scribing to remove residues and, following Cu plating, etched samples showed attenuated growths into the laser scribes with the contacts remaining electrically isolated. However, for single laser pass samples, ~40 µm wide parasitically-plated Cu stripes (Fig. 1e) were observed along the center of the laser cuts throughout the scribed pattern. Energy-dispersive x-ray spectroscopy (EDS) mapping confirmed the stripe consists of discrete Cu islands, isolated from the growing layer, that eventually coalesce during plating (Fig. 1f). This Cu-stripe feature was not observed for double laser pass samples, indicating differences in properties of the scribes with the different laser patterning conditions.The formation of the Cu-stripe is postulated to be the result of laser ablation and chemical etch damage to the insulating a-SiNx:H layer that opens pinholes to the more conductive c-Si wafer (Fig. 1g). These higher conductivity points produce localized conduits of enhanced current density, sufficient to nucleate Cu, and allow subsequent rapid growth of islands. In contrast, with plating to double pass processed samples, the more extensive laser damage to the a-SiNx:H layer exposes a significantly larger area of the Si wafer, which results in lower current densities insufficient to nucleate Cu. These observed effects of damage to both underlying layers and to growth habits of subsequent films, highlight the need for careful optimization and control of laser conditions during fabrication of photovoltaic devices.Front-junction Si-based solar cells with Al back contacts were etched and re-contacted with ED Cu to IBC-patterned Ni seed layers that had been evaporated through a shadow mask. Device performance showed little change, maintaining ~18% efficiency, with decreased device series resistance through improved RC. These results confirm ED Cu as a feasible and industrially-relevant approach for processing high quality metal contacts for Si-based solar cells. Figure 1

Optimization of Front Diffusion Profile in Bifacial Interdigitated Back Contact Solar Cell

The diffusion profiles of the front floating emitter (FFE) and front surface field (FSF) in a bifacial interdigitated back contact solar cell are optimized. The optimization results revealed that the FFE and FSF schemes are beneficial for enhancing the cell performance at the front and rear sides, respectively. Lighter doping is particularly better for the FSF scheme, and the FFE scheme requires a large diffusion depth for improving the performance. Increasing the area of the rear emitter boosts the performance of the cell, and an FFE scheme with 90% rear emitter area is found to be the best design. Quantum efficiency mapping demonstrated that the FFE scheme suppresses the loss at the back surface field region, thereby enhancing the performance of the total cell. The FSF scheme improves the quantum efficiency for the entire region by enhancing the carrier transport in the vertical direction. Furthermore, loss analysis revealed that the FFE scheme suppresses the recombination loss at the maximum power point, which is an important advantage over the FSF scheme.

Application of a Genetic Algorithm in Four-Terminal Perovskite/Crystalline-Silicon Tandem Devices

Perovskite/crystalline-silicon (c-Si) tandem solar cells offer a viable roadmap for reaching power conversion efficiencies beyond 30%. In this configuration, however, the silicon cell now mainly receives an infrared rich illumination spectrum where the absorption coefficient of silicon is poor. To boost the light absorption in this wavelength interval, transmitted through the top cell, a solution is to introduce a dedicated nanoscale texture on the front side of the silicon bottom cell and tweaking the optical elements in its design. These optical elements are manifold, with tunable geometrical dimensions, layer thicknesses, and refractive indices. For optically optimizing nanostructured silicon solar cells, electromagnetic wave solving methods, such as the rigorous coupled-wave analysis (RCWA), are normally used but they become computationally infeasible when several design variables are involved in an optimization problem. In this work, a natural selection algorithm, known as the genetic algorithm, is coupled with RCWA for extracting the optimal values of various design parameters in four-terminal perovskite/c-Si tandem devices in parallel. Both two-side-contacted and interdigitated back-contacted silicon heterojunction cell structures, featuring an inverse nanopyramid grating texture on the front, are optimized for five interdependent variables using a genetic algorithm for the bottom cell application and benchmarked against their random pyramid textured analogs. Our study shows that an optimized inverse nanopyramid grating texture can outperform the standard random pyramid texture when considering incidence angle variations. More importantly, the study illustrates how a genetic algorithm can support modeling complex solar cell structures with numerous degrees of freedom.