Voltage transient analysis as a generic tool for solar junction characterization

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An Enhanced Charge Carrier Separation in a Heterojunction Solar Cell with a Metal Oxide

A model of charge carrier transport in heterojunction solar cells composed of a solar light-absorbing semiconductor and a wide-bandgap semiconducting metal oxide is proposed. It describes an electric field in the semiconductor originating from the difference in the electron work functions between the two contacting materials, an enhanced hole separation by this field, and subsequent trap-assisted tunneling of holes through the semiconducting oxide. The model predicts a dramatic influence of the donor concentration in the semiconductor, trap parameters in the oxide, and ideality factor of the semiconductor/oxide heterojunction on the performance of the cell

Solution processed transition metal oxides selective contacts for Si heterojunction solar cells

Photovoltaics (PV) plays an increasingly important role as renewable energy to lower the carbon footprint and meet the world’s energy demand owing to its abundance. Silicon (Si) PV, attributed to its material abundance and processing experience leveraged from CMOS industry, dominates the PV market. Si heterojunctions cells, represented by heterojunction with intrinsic thin layer (HIT) technology, enable higher performance and lower fabrications cost, which has demonstrated the world champion efficiency of 26.7%. However, the p-type amorphous Si (a-Si) layer in this configuration suffers from parasitic absorption and high recombination. Therefore, alternatives materials, such as transition metal oxides (TMOs), with carrier selectivity similar to p-type a-Si that can improve current performance have attracted strong research interest. TMOs, such as MoO3, V2O5 and WO3 are originally applied in organic electronics as hole transport layers. TMOs, usually having large bandgap greater than 3 eV and are able to be processed at low temperature and are of low cost as a-Si. Most importantly, high theoretical work-function greater than 6.0 eV, are promising candidates to create an inversion layer at the n type Si (n-Si) surface resulting in an induced p-n junction for carrier separation as it is in Si heterojunction solar cell (HSCs). Most importantly, the carrier selectivity of TMOs is believed to be originated from oxygen vacancies related traps, through which carriers are extracted or transported through trap assisted tunnelling across the TMO and Si heterojunction. It has been reported that TMO/a-Si(i)/n-Si HSCs passivated with an a-Si:H layer have efficiency of 22.5 % with improved current performance, which is comparable to typical HIT cells with configuration of a-Si(p)/a-Si(i)/n-Si. Meanwhile, TMOs have demonstrated good passivation on Si, and thus simpler device configuration has been proposed without the a-Si(i) passivation layer. Such planar TMO/n-Si HSCs, embodied by MoOx/n-Si, V2Ox/n-Si and WOx/n-Si, have demonstrated the best efficiency of above 15.3%, and 15.7% and 12.5% respectively. It is noted that those reported TMOs/Si cells are based on thermal evaporation process for the deposition of the TMO layers, which requires expensive instruments and vacuum chamber. We have proposed to prepare TMO layers using sol-gel solution process. The obvious advantages are its fast, non-vacuum and room temperature process, and its potential for mass production. So far, HSCs based on solution processed TMOs (s-TMOs) on n-Si are not widely studied. In this work, we have first prepared hole selective contacts using solution processed MoOx (s-MoOx) by spin-coating and physical evaporated MoOx (e-MoOx) by electron beam evaporator. The performance of the s-MoOx/Si HSC has been investigated and optimized, which has been demonstrated solar cell efficiency of 12.5% for s-MoOx/Si HSC that is comparable to efficiency of 13.3% for e-MoOx/Si HSC. The performance of s-MoOx/Si HSC, to the best of our knowledge, is the highest among all solution processed TMO/Si HSCs and it is approaching others reported on e-MoOx/Si HSC. The slightly lower performance is mainly attributed to the slightly smaller open circuit voltage (Voc) and fill factor (FF) in the s-MoOx/Si HSCs. The investigation has shown that the slightly better performance in Voc and FF in e-MoOx/Si HSC is owing to the better carrier selectivity of 11.5 for e-MoOx film on Si in comparison to 10.1 for s-MoOx on Si. It is found that the lower carrier selectivity of s-MoOx on Si is due to the larger contact resistivity, but its contact recombination current density is better than e-MoOx on Si. The difference in the contact resistivity is believed to be associated with the trap profiles in the MoOx layer. Overall, this study has demonstrated the potentials to employ fast and convenient solution processed MoOx for Si HSCs with good cell performance. On the other hand, solution processed s-V2Ox and s-WOx thin films have been also investigated in terms of their material properties and applications in Si HSCs. The highest power conversion efficiency (PCE) of the planar for s-V2Ox/Si HSCs and s-WOx/Si HSCs after optimization is 10.8%, and 9.3% respectively. To best of our knowledge, the PCE of our planar s-V2Ox/Si HSCs is higher than other reported for solution processed s-V2Ox and the investigation and the performance for s-WOx/Si HSCs is the first reported. The performance of the s-WOx/Si HSCs lower owing to the smaller Voc because of the lower work function of only 4.71 eV in the s-WOx thin films. While there is the s-shape J-V characteristics overserved for s-V2Ox/Si HSCs lowering device FF, which is believed to be related to the energy distribution of the traps in the s-V2Ox thin films that is not favourable for trap-assisted tunnelling. The carrier selectivity of s-V2Ox and s-WOx contacts on Si was characterized, in which a lower selectivity of 8.06 was deduced for s-V2Ox and it is undetermined for s-WOx probably attributed to its weak inversion at the Si surface.Doctor of Philosoph

Design guideline for Si/organic hybrid solar cell with interdigitated back contact structure

We study the design of Si/organic hybrid (SOH) solar cells with interdigitated back contact (IBC) structure. SOH solar cells formed between n-Si and poly(3,4-ethylenedioxythiophene): polystyrenesulphonate (PEDOT:PSS) is a promising concept that combines the excellent electronic properties of Si with the solution-based processing advantage of an organic polymer. The IBC cell structure is employed to minimize parasitic absorption losses in the organic polymer, eliminate grid shadowing losses, and allow excellent passivation of the front Si surface in one step over a large area. The influence of Si thickness, doping concentration and contact geometry are simulated in this study to optimize the performance of the SOH-IBC solar cell. We found that a high power conversion efficiency of >20% can be achieved for optimized SOH-IBC cell based on a thin c-Si substrate of 40 μm thickness

Comparison of the effects of photodynamic therapy, intravitreal ranibizumab and combination for polypoidal choroidal vasculopathy under 1 + PRN regimen

Abstract Background The optimal treatment for polypoidal choroidal vasculopathy (PCV) is still under debate. Little knowledge is known about the treatment effect of “1+pro re nata(PRN)” treatment regimen for PCV. The aim of this study was to compare the outcomes of photodynamic therapy (PDT), intravitreal ranibizumab injection (IVR) and combination therapy under the “1 + PRN” treatment regimen for PCV. Methods Fifty-seven eyes of 57 patients completed the 12 months’ follow-up in this prospective study. The patients in the PDT arm(n = 23), ranibizumab arm(n = 18), or combination arm(n = 16) underwent a session of PDT, IVR or combination of both at baseline followed by additional IVR as needed. Mean change of logarithm of the minimal angle of resolution (logMAR) visual acuity (VA), central foveal thickness (CFT) and the regression rate of polyps were evaluated. Cost-benefit analysis was also performed. Results At Month 12, the mean logMAR VA improved from 0.90 ± 0.52 to 0.75 ± 0.57 in the PDT group (P  0.05). PDT treatment (60.87%) was superior to the IVR therapy (22.22%) in achieving complete regression of polyps (P < 0.05). Cost-benefit analysis showed that IVR treatment cost the least money for improving per 0.1logMAR units and the combination therapy demanded the least money for reducing per 100 μm of CFT. Conclusions PDT, IVR and the combination therapy have similar efficacy in the VA improvement as well as the reduction of CFT under the “1 + PRN” treatment regimen. Trial registration Current Controlled Trials NCT03459144. Registered retrospectively on March 2, 2018

Nanostructured back reflectors produced using polystyrene assisted lithography for enhanced light trapping in silicon thin film solar cells

We study light trapping in hydrogenated amorphous silicon thin film solar cells fabricated by plasma-enhanced chemical vapor deposition on various nanostructured back reflectors. The back reflectors are patterned using polystyrene assisted lithography. We have investigated the correlation between the back reflector optical properties and the corresponding solar cell performance. We have introduced double size polystyrene sphere patterned back reflectors and have provided experimental evidence for improved light trapping performance compared to single size polystyrene sphere patterned back reflectors. We have achieved high performing nanostructured amorphous silicon solar cells with an initial power conversion efficiency of 7.53% and over 20% enhancement of the short-circuit current compared with the reference flat solar cell

Retinal and Choroidal Alterations in Diabetic Retinopathy Treatment using Subthreshold Panretinal Photocoagulation with Endpoint Management Algorithm: A Secondary Analysis of a Randomized Clinical Trial

Abstract Introduction The aim of this study was to compare retinal and choroidal alterations in eyes with severe nonproliferative diabetic retinopathy (NPDR) after panretinal photocoagulation (PRP), using conventional pattern scan laser (PASCAL) and PASCAL with endpoint management (EPM). Methods This was a post hoc analysis of a paired randomized clinical trial. Bilateral treatment-naïve eyes of an individual with symmetric severe NPDR were randomly allocated into the threshold PRP group and subthreshold EPM PRP group. Patients had follow-up visits at 1, 3, 6, 9, and 12 months post-treatment. The retinal thickness (RT), choroidal thickness (CT), choroidal area, and choroidal vascularity index (CVI) were compared between the two groups and among different time points within the same group. Results Seventy eyes of 35 patients with diabetes mellitus (DM) were finally included for analysis at the 6- and 12-month visits, respectively. At 3 and 6 months post-treatment, the RT in the subthreshold EPM PRP group was significantly thinner than that in the threshold PRP group. CT, stromal area, and luminal area were reduced earlier in the threshold PRP group than in the subthreshold EPM PRP group. CVI was not significantly different within the same group or between groups at most time points. Conclusion At 12 months post-treatment, retinal thickening and choroidal disturbance may be slightly less severe and more delayed in eyes receiving PRP using PASCAL with EPM than in those receiving PRP using conventional PASCAL. The EPM algorithm may be a good alternative in PRP when treating severe NPDR. Trial Registration ClinicalTrials.gov identifier, NCT01759121

Atomically dispersed intrinsic hollow sites of M-M₁-M (M₁ = Pt, Ir; M = Fe, Co, Ni, Cu, Pt, Ir) on FeCoNiCuPtIr nanocrystals enabling rapid water redox

Fabrication of advanced electrocatalysts acting as an electrode for simultaneous hydrogen and oxygen evolution reactions (i.e., HER and OER) in an overall cell has attracted massive attention but still faces enormous challenges. This study reports a significant strategy for the rapid synthesis of high-entropy alloys (HEAs) by pulsed laser irradiation. Two types of intrinsic atomic hollow sites over the surface of HEAs are revealed that enable engaging bifunctional activities for water splitting. In this work, a novel senary HEA electrocatalyst made of FeCoNiCuPtIr facilitates the redox of water at only 1.51 V to achieve 10 mA cm−2 and still remains steadily catalytic and durable after being subjected to a 1m KOH solution for more than 20 h. First-principles calculations reveal that the incorporation of Ir and Pt atoms with neighboring elements donate valence electrons to hollow sites weakening the coupling strength between adsorbate and alloy surface and, consequently accelerating both HER and OER. This work delivers a powerful technique to synthesize highly efficient HEA catalysts and unravels the formation mechanism of active sites across the surface of HEA catalysts.Ministry of Education (MOE)The authors gratefully acknowledge the financial support from MOE Tier 1 RG193/17, MOE Tier 1 RG 79/20 (2020-T1-001-045), the Natural Science Foundation of Beijing Municipality (Grant No. 2212037), the National Natural Science Foundation of China (Grant No.51771027), and the Fundamental Research Funds for the Central Universities (Grant No. FRF-AT-20-07)

The Combination of Ketorolac with Local Anesthesia for Pain Control in Day Care Retinal Detachment Surgery: A Randomized Controlled Trial

This study aims to evaluate the efficacy of ketorolac with local anesthesia compared to local anesthesia alone for perioperative pain control in day care retinal detachment surgery. The randomized controlled trial included 59 eyes of 59 participants for retinal detachment surgery who were randomly assigned (1 : 1) into the ketorolac (K) group and control (C) group. All participants underwent conventional local anesthesia while patients in the K group received an extra administration of preoperative ketorolac. Participants in the K group had a statistically significantly lower intraoperative NRS score (median 1.0 versus 3.0, P=0.003), lower postoperative NRS score (median 0 versus 1.0, P=0.035), fewer proportion of rescue analgesic requirement (10% versus 34.5%, P=0.023), and lower incidence of postoperative nausea and vomiting (13.3% versus 41.4%, P=0.015) compared to the C group. Intraocular pressure (IOP) changes (△IOP) were significantly reduced in the K group (median 1.9 versus 3.0, P=0.038) compared to the C group 24 hours postoperatively. In conclusion, the combination of local anesthesia with ketorolac provides better pain control in retinal detachment surgery compared to local anesthesia alone. The beneficial effect of ketorolac with local anesthesia may contribute to a wider-spread adoption of day care retinal detachment surgery. This trial is registered with ClinicalTrials.gov NCT02729285

Optical Study and Experimental Realization of Nanostructured Back Reflectors with Reduced Parasitic Losses for Silicon Thin Film Solar Cells

We study light trapping and parasitic losses in hydrogenated amorphous silicon thin film solar cells fabricated by plasma-enhanced chemical vapor deposition on nanostructured back reflectors. The back reflectors are patterned using polystyrene assisted lithography. By using O2 plasma etching of the polystyrene spheres, we managed to fabricate hexagonal nanostructured back reflectors. With the help of rigorous modeling, we study the parasitic losses in different back reflectors, non-active layers, and last but not least the light enhancement effect in the silicon absorber layer. Moreover, simulation results have been checked against experimental data. We have demonstrated hexagonal nanostructured amorphous silicon thin film solar cells with a power conversion efficiency of 7.7% and around 34.7% enhancement of the short-circuit current density, compared with planar amorphous silicon thin film solar cells