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Origin of the tunable carrier selectivity of atomic-layer-deposited TiOx nanolayers in crystalline silicon solar cells
摘要： Titanium oxide (TiOx) nanolayers grown by atomic layer deposition are investigated with respect to their application as carrier selective contacts for crystalline silicon (c-Si) solar cells. Although TiOx is known to act as an electron contact, in this work the selectivity of TiOx layers is found to be widely tunable from electron to hole selective depending on deposition conditions, post-deposition treatments, and work function of the metal electrode used. Using TiOx and an intrinsic hydrogenated amorphous silicon buffer layer, solar cell test structure exhibiting open-circuit voltages (Voc) as high as 720 and 650 mV are shown for electron and hole selective contacts, respectively. Surface photovoltage and capacitance-voltage measurements reveal that carrier selectivity is correlated with the amount of c-Si band bending induced by TiOx, which are governed not only by the effective work function difference at the Si/TiOx interface, but also by the negative fixed charge present in the TiOx layer. This new finding is in contrast to the previous model for carrier transport where selectivity is determined only by the asymmetric band offsets at the Si/contact interface. It highlights the influence of induced band bending to produce carrier depletion/inversion conditions, and the importance of its selectivity effect in a c-Si absorber.
关键词： Titanium oxide,Solar cells,Carrier selective contacts,Atomic layer deposition
更新于2025-09-16 10:30:52
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The versatility of passivating carrier‐selective silicon thin films for diverse high‐efficiency screen‐printed heterojunction‐based solar cells
摘要： Providing state‐of‐the‐art surface passivation and the required carrier selectivity for both contacts, hydrogenated amorphous silicon thin films are the key components of silicon heterojunction (SHJ) solar cells. After intensive optimization of these layers for standard front and back contacted (FBC) n‐type cells, high surface passivation levels were achieved on cell precursors, demonstrated by minority carrier lifetimes exceeding 18 ms on float‐zone (FZ) and 11 ms on Czochralski (Cz) c‐Si wafers. The application of these very same layers on cheaper and commercially available Cz p‐type wafers resulted in similar passivation quality, with lifetimes above 10 ms as well. Large‐area industrial bifacial FBC SHJ cells processed on wafers taken along the full length of a high‐resistivity Cz p‐type ingot showed efficiencies in the 22.5% to 23% range, significantly higher than previously reported results on such substrates and on par with their n‐type counterparts. Best efficiencies on large‐area monofacial devices (>220 cm2) are 23.6% on Cz p‐type and 24.4% on Cz n‐type, similar to certified results obtained on lab‐scale cells (4 cm2), 23.76% on FZ p‐type and 24.21% on FZ n‐type. Notably, no specific adaptation of the reference n‐type cell process was necessary to achieve these results on p‐type material. Additionally, a 25% certified efficiency has been obtained on medium‐sized (25 cm2) interdigitated back‐contacted SHJ cells, featuring the same passivation layers developed for FBC devices. These results illustrate the versatility of the SHJ technology for various high‐efficiency screen‐printed solar cell configurations and show possible ways to improve its competitiveness on the global photovoltaic market.
关键词： solar cell,heterojunction,amorphous silicon,passivated contacts,crystalline silicon
更新于2025-09-12 10:27:22
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Highly Transparent Contacts to the 1D Hole Gas in Ultrascaled Ge/Si Core/Shell Nanowires
摘要： Semiconductor-superconductor hybrid systems have outstanding potential for emerging high performance nanoelectronics and quantum devices. However, critical to their successful application is the fabrication of high quality and reproducible semiconductor-superconductor interfaces. Here, we realize and measure axial Al-Ge-Al nanowire heterostructures with atomically precise interfaces, enwrapped by an ultra-thin epitaxial Si layer further denoted as Al-Ge/Si-Al nanowire heterostructures. The heterostructures were synthesized by a thermally induced exchange reaction of single-crystalline Ge/Si core/shell nanowires and lithographically defined Al contact pads. Applying this heterostructure formation scheme enables self-aligned quasi one-dimensional crystalline Al leads contacting ultra-scaled Ge/Si segments with contact transparencies greater than 96%. Integration into back-gated field-effect devices and continuous scaling beyond lithographic limitations allows us to exploit the full potential of the highly transparent contacts to the 1D hole gas at the Ge-Si interface. This leads to the observation of ballistic transport as well as quantum confinement effects up to temperatures of 150 K. Low temperature measurements reveal proximity-induced superconductivity in the Ge/Si core/shell nanowires. The realization of a Josephson field-effect transistor allows us to study the sub-gap structure caused by multiple Andreev reflections. Most importantly, the absence of a quantum dot regime indicates a hard superconducting gap originating from the highly transparent contacts to the 1D hole-gas, which is potentially interesting for the study of Majorana zero modes. Moreover, underlining the importance of the proposed thermally induced Al-Ge/Si-Al heterostructure formation technique, our system could contribute to the development of key components of quantum computing such as gatemon or transmon qubits.
关键词： 1D hole gas,hard superconducting gap,transparent contacts,superconductor-semiconductor hybrids,nanowire heterostructure,germanium
更新于2025-09-12 10:27:22
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For none, one, or two polarities—How do POLO junctions fit best into industrial Si solar cells?
摘要： We present a systematic study on the benefit of the implementation of poly‐Si on oxide (POLO) or related junctions into p‐type industrial Si solar cells as compared with the benchmark of Passivated Emitter and Rear Cell (PERC). We assess three aspects: (a) the simulated efficiency potential of representative structures with POLO junctions for none (=PERC+), one, and for two polarities; (b) possible lean process flows for their fabrication; and (c) experimental results on major building blocks. Synergistic efficiency gain analysis reveals that the exclusive suppression of the contact recombination for one polarity by POLO only yields moderate efficiency improvements between 0.23%abs and 0.41%abs as compared with PERC+ because of the remaining recombination paths. This problem is solved in a structure that includes POLO junctions for both polarities (POLO2), for whose realization we propose a lean process flow, and for which we experimentally demonstrate the most important building blocks. However, two experimental challenges—alignment tolerances and screen‐print metallization of p+ poly‐Si—are unsolved so far and reduced the efficiency of the “real” POLO2 cell as compared with an idealized scenario. As an intermediate step, we therefore work on a POLO IBC cell with POLO junctions for one polarity. It avoids the abovementioned challenges of the POLO2 structure, can be realized within a lean process flow, and has an efficiency benefit of 1.59%abs as compared with PERC—because not only contact recombination is suppressed but also the entire phosphorus emitter is replaced by an n+ POLO junction.
关键词： POLO,passivating contacts,solar cell development,efficiency potential,poly‐Si
更新于2025-09-12 10:27:22
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Hard mask processing of 20% efficiency back-contacted silicon solar cells with dopant-free heterojunctions
摘要： Single junction crystalline silicon (c-Si) solar cells featuring a conventionally doped interdigitated back contact heterojunction (IBC-SHJ) structure has approached a record efficiency of 26.6%, which is very close to the practical limit. However, integrating the interdigital p- and n-type amorphous silicon (a-Si:H) layers on the rear surface of Si substrate is of such complexity, posing problem of heavy dependences on expensive manufacturing techniques including plasma-enhanced chemical vapor deposition and photolithography. Its commercial potential is thus always being questioned, and to seek an alternative fabrication procedure, which adapts to cost-effective deposition parallel with simple patterning characteristics, has been a primary research target of related subjects. Here, we demonstrated 20.1% efficiency dopant-free IBC-SHJ solar cells by combining evaporated carrier-selective materials (MoOx and LiFx) and two-steps hard masks alignments, delivering substantial simplifications in the architecture and fabrication procedures. We investigated the effect of intrinsic a-Si:H films with different thicknesses on the passivation and contact resistance for both a-Si:H/MoOx and a-Si:H/LiFx contacts, showing 4 nm a-Si:H is better for high efficiency IBC-SHJ solar cells. We also found that the position of the metal target (electrode definition step) and isolation in between the busbar and the Si substrate are highly relevant to leakage and recombination and have great impact on the device performance. The dopant-free IBC-SHJ solar cells demonstrated here manifest enough confidence in our hard mask based fabrication procedure, with great potential for high performance-to-cost ratio in future.
关键词： solar cells,dopant-free,interdigitated back contact,silicon,carrier-selective,contacts,heterojunction
更新于2025-09-12 10:27:22
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Infrared laser based contacting of bar-wound windings in the field of electric drives production
摘要： Driven by electric mobility innovative winding methods increasing the copper fill ratio and thus the power density of electrical drives gain in importance. Compared to conventional windings, bar-wound windings based on rectangular cross sections besides optimized copper fill ratios also offer advantages in terms of automated production. Because of the high number of joints necessary for the manufacturing of the winding, contacting efforts increase significantly wherefore the process of laser welding, due to its short process times and high reproducibility shows potentials to realize the process step. This paper examines the most important interactions within the process of laser welding of insulated copper wires with rectangular cross sections in the context of electric drives production. Besides workpiece specific factors, the focus is set on process parameters, beam guidance strategies and specific quality requirements. For this purpose, a parameter study based on design of experiments is executed in which suitable measuring technologies are used to quantify the properties of the samples.
关键词： hairpin windings,infrared lasers,electrical contacts,insulated copper conductors,laser beam welding
更新于2025-09-12 10:27:22
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AIP Conference Proceedings [AIP Publishing 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Fes, Morocco (25–27 March 2019)] 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Characterization of absorption losses in rear side n-type polycrystalline silicon passivating contacts
摘要： Passivating contacts consisting of polycrystalline silicon (poly-Si) and thin silicon-oxide (SiOx) layers facilitate a significant reduction of recombination losses in silicon solar cells. Nevertheless, these gains come with short circuit current density (Jsc) losses due to parasitic absorption by the poly-Si. Even if the passivating contacts are employed at the rear side only, absorption, particularly due to free carriers (FCA) in the heavily doped poly-Si, may still lead to significant Jsc losses. In this work, these losses are characterized as a function of the poly-Si thickness (tpoly) by the analysis of front reflectance spectra in the infrared (IR). For this study, two sets of samples with different n-type full-area poly-Si passivating contacts at the rear are compared to references with a phosphorus(P)-diffused back surface field (BSF) instead. For the two sets, Jsc losses with respect to the references (ΔJsc) are 0.10 mA/cm2 and 0.42 mA/cm2 per 100 nm thick poly-Si, respectively. The difference between the two values is studied by Hall measurements and interpreted to be due to the over three times as high free carrier concentration (ND,act) in the poly-Si layers of the second set of samples as the first set. On the other hand, lifetime measurements showed an excellent passivation yielding an implied open circuit voltage (iVoc) up to 736 mV only for the samples with the more heavily doped poly-Si, whereas iVoc of 683 mV was measured for the first set, which indicates a trade-off between absorption losses and passivation quality.
关键词： infrared reflectance,passivating contacts,solar cells,absorption losses,polycrystalline silicon
更新于2025-09-12 10:27:22
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An Investigation of Internal Quantum Efficiency of Bifacial Interdigitated Back Contact (IBC) Crystalline Silicon Solar Cell
摘要： In this article, we investigated the internal quantum efficiency (IQE) properties of n-type bifacial interdigitated back contact crystalline silicon solar cells using an IQE mapping system. In the cell structure, high and low IQE values were observed above the emitter and back surface field (BSF) regions. The IQE values above the BSF busbar were drastically reduced due to electrical shading loss. Line scan profiles at different wavelengths showed the detailed distribution of IQE values. The IQE values varied greatly depending not only on the difference between emitter and BSF regions but also on the rear side structure such as the electrode width and the distance between the emitter and BSF regions. On the other hand, the IQE spectra at over 950 nm improved by increasing the light absorbance ratio from the rear side. After module formation, the IQE spectra at short wavelengths were significantly reduced. The IQE properties were obtained from the front and rear sides. The difference in the short-circuit current between front side illumination and rear side illumination was mainly due to optical shading loss and carrier recombination loss at the BSF region. For a high cell efficiency, it is necessary to improve the passivation properties of the BSF region and optimize the electrode design.
关键词： Back contacts,internal quantum efficiency,silicon solar cells
更新于2025-09-12 10:27:22
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Anodically electrodeposited NiO nanoflakes as hole selective contact in efficient air processed p-i-n perovskite solar cells
摘要： Nanostructured NiO as hole selective contact for perovskite solar cells is deposited on ITO from the potentiostatic anodic electrodeposition of NiOOH. Along with the large surface extension due to the honeycomb-like morphology, the electrodeposition route imparts different electrochemical features in respect to the classic sol-gel derived NiO, which are two interesting features for optoelectronic applications. CH3NH3PbI3 is deposited in ambient atmosphere on the NiO substrates to fabricate p-i-n perovskite solar cells, with PCBM and solution processed BCP as electron selective contact and silver as counter electrode. We found that the performances are strongly dependent on the deposition potential, with the PCE increasing when going from 1.00 V to 1.10 V vs Ag/AgCl. The best efficiency obtained is 16.1%, thanks to a fill-factor of 78%. Notably, the electrodeposited layer outperformed the sol-gel spin-coated one, proving the effectiveness of electrosynthesis to achieve competitive selective contacts for perovskite photovoltaics.
关键词： Perovskite solar cells,Selective contacts,Electrodeposition,Nickel oxide
更新于2025-09-12 10:27:22
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Mitigating Plasmonic Absorption Losses at Rear Electrodes in High‐Efficiency Silicon Solar Cells Using Dopant‐Free Contact Stacks
摘要： Although charge-carrier selectivity in conventional crystalline silicon (c-Si) solar cells is usually realized by doping Si, the presence of dopants imposes inherent performance limitations due to parasitic absorption and carrier recombination. The development of alternative carrier-selective contacts, using non-Si electron and hole transport layers, has the potential to overcome such drawbacks and simultaneously reduce the cost and/or simplify the fabrication process of c-Si solar cells. Nevertheless, devices relying on such non-Si contacts with power conversion efficiencies (PCEs) that rival their classical counterparts are yet to be demonstrated. In this study, one key element is brought forward toward this demonstration by incorporating low-pressure chemical vapor deposited ZnO as the electron transport layer in c-Si solar cells. Placed at the rear of the device, it is found that rather thick (75 nm) ZnO film capped with LiFx/Al simultaneously enables efficient electron selectivity and suppression of parasitic infrared absorption. Next, these electron-selective contacts are integrated in c-Si solar cells with MoOx-based hole-collecting contacts at the device front to realize full-area dopant-free-contact solar cells. In the proof-of-concept device, a PCE as high as 21.4% is demonstrated, which is a record for this novel device class and is at the level of conventional industrial solar cells.
关键词： ZnO,plasmonic absorption,c-Si solar cells,carrier-selective contacts,dopant-free contacts
更新于2025-09-11 14:15:04