- 标题
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A unified figure of merit for interband and intersubband cascade devices
摘要： By exploring a semi-empirical model, the saturation current density J0 is identified to manifest the significant difference in carrier lifetime between interband cascade devices (ICDs) and intersubband quantum cascade devices (QCDs). Based on this model, the values of J0 have been extracted for a large number of ICDs and QCDs from their current-voltage characteristics at room temperature. By analyzing and comparing available ICD and QCD data, we demonstrate how J0 can be used as a unified figure of merit to evaluate both interband and intersubband cascade configurations for their device functionality. The significance of J0 on the performances of mid-infrared detectors and photovoltaic cells is illustrated by comparing the measured detectivity (D*) and the estimated open-circuit voltage (Voc), respectively. From extracted values of J0, which are more than one order of magnitude lower in ICDs than that in QCDs with similar transition energies in active regions, and discussion of the consequences on device performance, the advantages of interband cascade configurations over intersubband quantum cascade configurations have been clearly revealed based on the same framework. The overall picture for both QCDs and ICDs sheds light from the perspective of a united figure of merit, which will provide useful guidance and stimulation to the future development of both ICDs and QCDs.
关键词： Saturation current density,Interband cascade,Quantum cascade,Open-circuit voltage
更新于2025-09-23 15:22:29
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - On the impact of the metal work function on the recombination in passivating contacts using quasi-steady-state photoluminescence
摘要： Understanding the impact of metal contacts on the recombination within a passivated silicon wafer is crucial for the optimization of various photovoltaic devices such as passivating-contact-based solar cells. To investigate the effect of the metal work function, a selection of metals is applied to aluminum-oxide-passivated n-type crystalline silicon wafers. The saturation current density of the metalized contact (J0m) is determined using the quasi-steady-state photoluminescence method and used as a figure of merit to quantify the effect. We find that J0m increases with the metal work function and that this effect is modulated with the passivation layer thickness. It is more pronounced for thinner passivation layers, which can be attributed to a significant change in the populations of electrons and holes near the silicon surface induced by the metal. Meanwhile thicker layers prevent the charge transfer between the silicon and metal more efficiently leading to insignificant changes in J0m. Based on these findings, we suggest a suitable metal work function range to optimize contact recombination in silicon-based solar cells.
关键词： passivating contacts,surface recombination,saturation current density,quasi-steady-state photoluminescence,work function,Effective lifetime,silicon solar cells
更新于2025-09-23 15:21:01
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Correlation between the open-circuit voltage and recombination loss at metal-silicon interfaces of crystalline silicon solar cells
摘要： For screen-printed silicon solar cells, optimization of the contact characteristics between the front metal electrode and silicon is very significant for realizing high efficiency. As technology advances, the solar cell efficiency has been steadily increased. Especially, as surface recombination becomes more important in high efficiency solar cells, understanding and controlling recombination in the metal contact area are necessary. Recombination at the metal-silicon interface is a major cause of the drop in the open-circuit voltage (Voc) of a solar cell. Thus far, the study of electrodes in silicon solar cells has been largely aimed at reducing the series resistance, and few studies on recombination due to electrodes have been performed. Quantitatively evaluating the recombination in electrodes to assess the effect on the efficiency is expected to become more important in the near future. In this paper, the contact characteristics of a screen-printed silver electrode and silicon interface were analyzed using saturation current density (Jo) measurements according to the surface doping concentration and firing temperature. The effects of the contact characteristics on Voc and recombination were also investigated. Experimental results showed that Jo.pass decreased with decreasing surface doping concentration and Jo.metal increased with increasing surface doping concentration and firing temperature. For quantitative analysis of Jo.metal, the size and distribution of Ag crystallites were observed using SEM and TEM, and the Ag concentration was analyzed by ICP-OES measurements. The larger Jo.metal was, the higher the Ag crystallite concentration, indicating that the Ag crystallites under the electrode increased Jo.metal. The effect of Jo.metal on the electrical characteristics of the solar cell was analyzed by calculating the change in the surface recombination velocity and the decreased width of Voc. Through this study, the recombination in the metallized area, which is expected to become increasingly important, and particularly the effects of the doping profile of the emitter region and silver crystallites on the surface recombination were quantitatively assessed. The amount of silver crystallites on the silicon wafer was quantitatively analyzed.
关键词： Screen-printed silicon solar cells,Saturation current density,Open-circuit voltage,Ag crystallites,Recombination loss,Metal-silicon interface
更新于2025-09-23 15:19:57
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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) - Impact of the thermal budget of the emitter formation on the pFF of PERC+ solar cells
摘要： We develop processes for advanced phosphorus doping profiles in order to reduce the emitter saturation current density Jo,e of industrial bifacial PERC+ solar cells. With an in-situ oxidation, which takes place in the POCl3 furnace in between the deposition and the drive-in step, the surface concentration was lowered from 3 × 1020 cm-3 to 1.7 × 1020 cm-3. With an additional ex-situ oxidation, which takes place after the phosphorus silicate glass is removed, the phosphorus surface concentration was further reduced to 3 × 1019 cm- 3. The decreased phosphorus surface concentration drastically reduces Jo,e from 106 fA/cm2 down to 22 fA/cm2. The reduced Jo,e increases the implied open circuit voltage up to 712 mV of unmetallized PERC+ test structures and the Voc of PERC+ solar cells up to 678 mV and efficiencies up to 21.8%. However, our solar cell analysis reveals for the first time, that with increasing thermal budget of the applied POCl3 and oxidation recipes the pseudo fill factor (pFF) decreases by up to 1.5%. This corresponds to an efficiency loss of approximately 0.5%abs. We analyse the pFF loss based on different lifetime test structures representing the emitter or the bulk of the PERC+ solar cell. From the lifetime measurements we calculate I-V curves representing the implied fill factor (iFF) of the different parts of the PERC+ solar cell as well as a combined one for the whole cell, which compares well to the measured pFF. The iFF values clearly show that the pFF is mainly limited by wafer bulk material. However, also the iFF values of the emitter slightly decrease with increasing thermal budget.
关键词： in-situ oxidation,phosphorus doping profiles,pseudo fill factor,ex-situ oxidation,emitter saturation current density,PERC+ solar cells,thermal budget
更新于2025-09-12 10:27:22
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High-performance black phosphorus field-effect transistors with long-term air-stability
摘要： Two-dimensional layered materials (2DLMs) are of considerable interest for high-performance electronic devices for their unique electronic properties and atomically thin geometry. However, the atomically thin geometry makes their electronic properties highly susceptible to the environment changes. In particular, some 2DLMs (e.g., black phosphorus (BP) and SnSe2) are unstable and could rapidly degrade over time when exposed to ambient conditions. Therefore, the development of proper passivation schemes that can preserve the intrinsic properties and enhance their lifetime represents a key challenge for these atomically thin electronic materials. Herein we introduce a simple, non-disruptive and scalable van der Waals passivation approach by using organic thin films to simultaneously improve the performance and air stability of BP field-effect transistors (FETs). We show that dioctylbenzothienobenzothiophene (C8-BTBT) thin films can be readily deposited on BP via van der Waals epitaxy approach to protect BP against oxidation in ambient conditions over 20 days. Importantly, the non-covalent van der Waals interface between C8-BTBT and BP effectively preserves the intrinsic properties of BP, allowing us to demonstrate high-performance BP FETs with a record-high current density of 920 μA/um, hole drift velocity over 1 ⅹ 107 cm/s, and on/off ratio of 104~107 at room temperature. This approach is generally applicable to other unstable two-dimensional (2D) materials, defining a unique pathway to modulate their electronic properties and realize high-performance devices through hybrid heterojunctions.
关键词： black phosphorus,saturation velocity,saturation current density,two-dimensional materials,passivation,field effect transistors
更新于2025-09-10 09:29:36