Si-based photovoltaic and photoelectrochemical cells for high-efficiency solar energy harvesting

Rapidly growing consumption of energy derived from carbon-based fossil fuel has caused energy crises, global warming, and air pollution. Therefore, the development of renewable energy is required. Solar energy has been considered as a promising renewable energy source since it is clean, inexhaustible, and abundant in nature. Therefore, many technologies have been studied for harvesting solar energy including photovoltaics, solar heating, concentrating solar power, and solar-driven water splitting. In this dissertation, we demonstrate a variety of approaches for improving solid-state devices for harvesting solar energy via the photovoltaic effect or photoelectrochemical water splitting. First, we demonstrate improved passivation quality for Si photovoltaic devices using i a-Si:H films with a gradient-layered structure consisting of interfacial, transition, and capping layers deposited on c-Si surfaces. The H₂ dilution ratio (R) during deposition was optimized individually for the interfacial and capping layers, which were separated by a transition layer for which R changed gradually between its values for the interfacial and capping layers. This approach yielded a significant reduction in surface carrier recombination, resulting in improvement of the minority carrier lifetime from 1480 μs for mono-layered i a-Si:H passivation to 2550 μs for the gradient-layered passivation approach. We then demonstrate approaches for design and fabrication of Si-based photoelectrochemical devices that demonstrate high performance and stability for solar-driven water splitting. Metal-insulator-semiconductor (MIS) structures are widely used in Si-based solar water splitting photoelectrodes to protect the Si layer from corrosion. Typically, there is a tradeoff between efficiency and stability when optimizing insulator thickness. In this study, we demonstrate improved Si-based MIS photoanodes with thick insulating layers fabricated using thin-film reactions to create localized conduction paths through the insulator and electrodeposition to form metal catalyst islands. These fabrication approaches are low-cost and highly scalable, and yield MIS photoanodes with low onset potential, high saturation current density, and excellent stability. By combining this approach with a p⁺n-Si buried junction, further improved oxygen evolution reaction (OER) performance is achieved with an onset potential of 0.7 V versus reversible hydrogen electrode (RHE) and saturation current density of 32 mA/cm² under simulated AM1.5G illumination. A two-step Ni/NiFe electrodeposition process is then demonstrated to create more efficient OER catalysts. The Ni/NiFe catalyst layers increase Schottky barriers between Si and metal catalyst and lower the photoanode onset potential, improving applied bias photon conversion efficiency (ABPE) to a Ni catalyst, to 3.5%.Electrical and Computer Engineerin

Wafer-Scale Si-Based Metal−Insulator−Semiconductor Photoanodes for Water Oxidation Fabricated Using Thin Film Reactions and Multiple-layer Electrodeposited Catalysts

Solar-driven photoelectrochemical (PEC) water splitting offers a promising and environmentally friendly route for the conversion of renewable solar energy to hydrogen gas. A crystalline Si absorber is especially attractive due to its moderate bandgap, high charge mobility, long carrier diffusion length, costeffectiveness, and scalability in manufacturing. To improve the stability of Si-based PEC cells in operation, metal−insulator− semiconductor (MIS) structures have been widely employed. In this work, we employ simple and highly scalable processes to fabricate high-performance, extremely stable Si-based MIS photoanodes, and demonstrate their application to the fabrication of wafer-scale photoanodes. Localized conduction paths formed via an Al/SiO2 thin-film reaction enable low-resistance charge extraction even through thick insulating layers, yielding photoanodes with excellent stability. To improve the efficiency, we demonstrate a twostep Ni/NiFe electrodeposition process to create efficient oxygen evolution reaction catalysts. The Ni/NiFe catalyst allows for a high Schottky barrier between Si and Ni, lowering the photoanode onset potential, while the NiFe surface layer improves the catalytic performance. An unassisted solar-driven water splitting system incorporating a wafer-scale photoanode and monocrystalline Si solar cells is demonstrated and yields a solar-to-hydrogen conversion efficiency of 6.9% under simulated AM 1.5G sunlight illumination.This research was primarily supported by the National Science Foundation (grant CBET-2109842). The authors acknowledge the use of the facilities and instrumentation supported by Texas Materials Institute, and by the National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement nos. DMR-1720595 and DMR-2308817. This work was performed in part at the University of Texas Microelectronics Research Center, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science Foundation (grant ECCS-2025227).Center for Dynamics and Control of Material

Challenges in Improving Performance of Oxide Thermoelectrics Using Defect Engineering

Oxide thermoelectric materials are considered promising for high-temperature thermoelectric applications in terms of low cost, temperature stability, reversible reaction, and so on. Oxide materials have been intensively studied to suppress the defects and electronic charge carriers for many electronic device applications, but the studies with a high concentration of defects are limited. It desires to improve thermoelectric performance by enhancing its charge transport and lowering its lattice thermal conductivity. For this purpose, here, we modified the stoichiometry of cation and anion vacancies in two different systems to regulate the carrier concentration and explored their thermoelectric properties. Both cation and anion vacancies act as a donor of charge carriers and act as phonon scattering centers, decoupling the electrical conductivity and thermal conductivity

Preventing condensation of objective lens in noncontact wide-angle viewing systems during vitrectomy

AIM: To assess the optimal conditions for preventing condensation of objective lens during vitrectomy with noncontact wide-angle viewing systems (WAVSs). METHODS: We explored the effectiveness of the coating with ophthalmic viscoelastic device (OVDs) on the corneal surface and the soaking the objective lens in warm-saline for preventing condensation of objective lens. First, to find the optimal soaking time to keep the objective lens warm, we measured the temperature of objective lens every minute after soaking in warm saline. Second, to find optimal distance between cornea and objective lens, which provide as wide a view as possible and less condensation at the same time, we measured the condensation time with different distances. With the obtained optimal soaking time and distance, we explored the effect of coating cornea with OVDs and soaking objective lens in warm saline on condensation time. RESULTS: One and 5min of soaking in warm saline was most effective for keeping the lens warm enough (45.1℃±2.1℃ for 1min and 46.4℃±1.0℃ for 5min, P=0.109). The mean condensation times for the control group at 1, 3, and 5 mm from corneal surface to objective lens were 1±0.4, 4±1.4, 190±26.1s, respectively, thus 5 mm was most optimal distance for vitrectomy with WAVSs. For the OVD coating group, the mean condensation times were 1.5±0.3, 13±1.4, and 200±23.9s at 1, 3, and 5 mm distance and borderline significant compared with control group (P=0.068, 0.051, and 0.063, respectively). With the 1-minute warm saline soaking group, the mean condensation time were extended to 188±34.4, 416±65.7, and 600±121.3s at 1, 3, and 5 mm distance and statistically significant compared with control (P=0.043, 0.041 and 0.043, respectively). CONCLUSION: OVD coating on corneal surface shows no difference on condensation time with control group. However, soaking the objective lens in warm saline revealed statistically significant extension of condensation time compared to control group. Therefore, keeping the objective lens warm with soaking in warm saline is a simple but effective to prevent condensation of objective lens during vitrectomy. The thermodynamics between objective lens and cornea during vitrectomy warrants further investigation

Scalable, highly stable Si-based metal-insulator-semiconductor photoanodes for water oxidation fabricated using thin-film reactions and electrodeposition

Metal-insulator-semiconductor (MIS) structures are widely used in Si-based solar water- splitting photoelectrodes to protect the Si layer from corrosion. Typically, there is a tradeoff between efficiency and stability when optimizing insulator thickness. Moreover, lithographic patterning is often required for fabricating MIS photoelectrodes. In this study, we demon- strate improved Si-based MIS photoanodes with thick insulating layers fabricated using thin- film reactions to create localized conduction paths through the insulator and electro- deposition to form metal catalyst islands. These fabrication approaches are low-cost and highly scalable, and yield MIS photoanodes with low onset potential, high saturation current density, and excellent stability. By combining this approach with a p +n-Si buried junction, further improved oxygen evolution reaction (OER) performance is achieved with an onset potential of 0.7 V versus reversible hydrogen electrode (RHE) and saturation current density of 32 mA/cm 2 under simulated AM1.5G illumination. Moreover, in stability testing in 1 M KOH aqueous solution, a constant photocurrent density of ~22 mA/cm 2 is maintained at 1.3 V versus RHE for 7 days.Part of this work was supported by the National Science Foundation (CBET-1702944). This research was partially supported by the National Science Foundation through the Center for Dynamics and Control of Materials: an NSF MRSEC under Cooperative Agreement No. DMR-1720595. This work was performed in part at the University of Texas Microelectronics Research Center, a member of the National Nanotechnology Coordinated Infrastructure (NNCI), which is supported by the National Science Foun- dation (ECCS-2025227).Center for Dynamics and Control of Material

An Optimization of Composition Ratio among Triple-Filled Atoms in In

Bulk nanostructured materials are important as energy materials. Among thermoelectric materials, the skutterudite system of CoSb3 is a representative material of bulk nanostructured materials. Filling a skutterudite structure with atoms that have different localized frequencies (also known as triple filling) was reported to be effective for lowering thermal conductivity. Among studies representing superior power factors, In-filled skutterudite systems showed higher Seebeck coefficients. This study sought to optimize the composition ratio among the triple-filled atoms in an In0.3-x-yBaxCeyCo4Sb12 system. The composition dependence of the thermoelectric properties was investigated for specimens with different ratios among the three kinds of filler atoms in the In0.3-x-yBaxCeyCo4Sb12 system. In addition, the process variables were carefully optimized for filled skutterudite systems to obtain a maximum ZT value

Impact of components of metabolic syndrome on the risk of adverse renal outcomes in patients with atrial fibrillation: a nationwide cohort study

Background: The renal effect of metabolic syndrome components is unclear in patients with atrial fibrillation. This study aimed to investigate the association between metabolic syndrome components and incident end-stage renal disease among patients with atrial fibrillation. Methods: A total of 202,434 atrial fibrillation patients without prevalent end-stage renal disease were identified from the National Health Insurance Service database between 2009 and 2016. We defined the metabolic score range from 0 to 5 points such that a patient received every 1 point if the patient met each component listed in the diagnostic criteria of metabolic syndrome. The population was divided into 6 groups: MS 0–MS 5 for a metabolic score of 0–5, respectively. Multivariate Cox regression analysis was used to estimate the risks of end-stage renal disease. Results: There were 12,747, 31,059, 40,361, 48,068, 46,630, and 23,569 patients for MS 0–MS 5, respectively. Compared with MS 0, MS 5 had a higher CHA 2DS 2-VASc score (3.8 vs. 1.0) (P &lt;.001). During a median follow-up of 3.5 years, compared with MS 0, MS 1–MS 5 were associated with a gradually increasing incidence of end-stage renal disease, in relation to an increase in the metabolic score, (log-rank P &lt;.001). After multivariate adjustment, a higher metabolic score was associated with a greater risk of incident end-stage renal disease: adjusted hazard ratio [95% confidence interval] = 1.60 [0.78–3.48], 2.08 [1.01–4.31], 2.94 [1.43–6.06], 3.71 [1.80–7.66], and 4.82 [2.29–10.15], for MS 1–MS 5, respectively. Conclusions: Metabolic syndrome components additively impacts the risk of incident end-stage renal disease among patients with atrial fibrillation.</p

Cumulative burden of metabolic syndrome and its components on the risk of atrial fibrillation:a nationwide population-based study

BackgroundThe metabolic syndrome (MetS) and its components are associated with the development of atrial fibrillation (AF). However, the impact of time-burden of MetS on the risk of AF is unknown. We investigated the effect of the cumulative longitudinal burden of MetS on the development of AF.MethodsWe included 2 885 189 individuals without AF who underwent four annual health examinations during 2009-2013 from the database of the Korean national health insurance service. Metabolic burdens were evaluated in the following three ways: (1) cumulative number of MetS diagnosed at each health examination (0-4 times); (2) cumulative number of each MetS component diagnosed at each health examination (0-4 times per MetS component); and (3) cumulative number of total MetS components diagnosed at each health examination (0 to a maximum of 20). The risk of AF according to the metabolic burden was estimated using Cox proportional-hazards models.ResultsOf all individuals, 62.4%, 14.8%, 8.7%, 6.5%, and 7.6% met the MetS diagnostic criteria 0, 1, 2, 3, and 4 times, respectively. During a mean follow-up of 5.3 years, the risk of AF showed a positive association with the cumulative number of MetS diagnosed over four health examinations: adjusted hazard ratios (HRs) with 95% confidence intervals (CIs) of 1, 2, 3, and 4 times compared to 0 times were 1.18 (1.13-1.24), 1.31 (1.25-1.39), 1.46 (1.38-1.55), and 1.72 (1.63-1.82), respectively; P for trend ConclusionsGiven the positive correlations between the cumulative metabolic burdens and the risk of incident AF, maximal effort to detect and correct metabolic derangements even before MetS development might be important to prevent AF and related cardiovascular diseases