Silver Doped Cu2SnS3 Absorber Layers for Solar Cells Application

The p-type semiconductorCu2SnS3 is alloyedwithAg to investigate its effect on absorber layer and solar cell properties. Ag replaces the Cu in (Cu1-xAgx)2SnS3 (ACTS) up to x ≥ 6% at 550 °C. Above this percentage, Ag forms secondary phases.We find a significant increase in grain size, from hundreds of nanometers to severalmicrons, and increased photoluminescence yield with increasing Ag concentration. Low-temperature photoluminescence measurements show that compensation is increased for the ACTS absorber layers, which could be beneficial for CTS, but also that the electrostatic band gap fluctuations are increased. The external quantum efficiency of the solar cells made from ACTS shows an increased carrier collection length from 320 nm for CTS to 700 nm and a thicker buffer layer. We attribute the increase in collection length to both increased depletion width (increased compensation) and diffusion length (larger grains). Overall the ACTS solar cells have a lower power conversion efficiency due to lower shunt resistance and open-circuit voltage, which are attributed to increase in pinholes, electrostatic fluctuation, and changes at the CdS/ACTS interface

Optical lithography patterning of SiO2 layers for interface passivation of thin film solar cells

Ultrathin Cu(In,Ga)Se2 solar cells are a promising way to reduce costs and to increase the electrical performance of thin film solar cells. In this work, we develop an optical lithography process that can produce sub-micrometer contacts in a SiO2 passivation layer at the CIGS rear contact. Furthermore, an optimization of the patterning dimensions reveals constrains over the features sizes. High passivation areas of the rear contact are needed to passivate the CIGS interface so that high performing solar cells can be obtained. However, these dimensions should not be achieved by using long distances between the contacts as they lead to poor electrical performance due to poor carrier extraction. This study expands the choice of passivation materials already known for ultrathin solar cells and its fabrication techniques.publishe

Upconversion in solar cells

Abstract The possibility to tune chemical and physical properties in nanosized materials has a strong impact on a variety of technologies, including photovoltaics. One of the prominent research areas of nanomaterials for photovoltaics involves spectral conversion. Modification of the spectrum requires down-and/or upconversion or downshifting of the spectrum, meaning that the energy of photons is modified to either lower (down) or higher (up) energy. Nanostructures such as quantum dots, luminescent dye molecules, and lanthanide-doped glasses are capable of absorbing photons at a certain wavelength and emitting photons at a different (shorter or longer) wavelength. We will discuss upconversion by lanthanide compounds in various host materials and will further demonstrate upconversion to work for thin-film silicon solar cells

Limited life cycle and cost assessment for the bioconversion of lignin-derived aromatics into adipic acid

Lignin is an abundant and heterogeneous waste byproduct of the cellulosic industry, which has the potential of being transformed into valuable biochemicals via microbial fermentation. In this study, we applied a fast-pyrolysis process using softwood lignin resulting in a two-phase bio-oil containing monomeric and oligomeric aromatics without syringol. We demonstrated that an additional hydrodeoxygenation step within the process leads to an enhanced thermochemical conversion of guaiacol into catechol and phenol. After steam bath distillation, Pseudomonas putida KT2440-BN6 achieved a percent yield of cis, cis-muconic acid of up to 95 mol% from catechol derived from the aqueous phase. We next established a downstream process for purifying cis, cis-muconic acid (39.9 g/L) produced in a 42.5 L fermenter using glucose and benzoate as carbon substrates. On the basis of the obtained values for each unit operation of the empirical processes, we next performed a limited life cycle and cost analysis of an integrated biotechnological and chemical process for producing adipic acid and then compared it with the conventional petrochemical route. The simulated scenarios estimate that by attaining a mixture of catechol, phenol, cresol, and guaiacol (1:0.34:0.18:0, mol ratio), a titer of 62.5 (g/L) cis, cis-muconic acid in the bioreactor, and a controlled cooling of pyrolysis gases to concentrate monomeric aromatics in the aqueous phase, the bio-based route results in a reduction of CO2 -eq emission by 58% and energy demand by 23% with a contribution margin for the aqueous phase of up to 88.05 euro/ton. We conclude that the bio-based production of adipic acid from softwood lignins brings environmental benefits over the petrochemical procedure and is cost-effective at an industrial scale. Further research is essential to achieve the proposed cis, cis-muconic acid yield from true lignin-derived aromatics using whole-cell biocatalysts

On the importance of joint mitigation strategies for front, bulk, and rear recombination in ultrathin Cu(In,Ga)Se2 solar cells

Several optoelectronic issues, such as poor optical absorption and recombination limit the power conversion efficiency of ultrathin Cu(In,Ga)Se2 (CIGS) solar cells. To mitigate recombination losses, two combined strategies were implemented: a Potassium Fluoride (KF) Post-Deposition Treatment (PDT) and a rear interface passivation strategy based on an Aluminium Oxide (Al2O3) point contact structure. The simultaneous implementation of both strategies is reported for the first time on ultrathin CIGS devices. Electrical measurements and 1-D simulations demonstrate that, in specific conditions, devices with only KF-PDT may outperform rear interface passivated based devices. By combining KF-PDT and rear interface passivation, an enhancement in open-circuit voltage of 178 mV is reached over devices that have a rear passivation only and of 85 mV over devices with only a KF-PDT process. Time-Resolved Photoluminescence measurements showed the beneficial effects of combining KF-PDT and the rear interface passivation at decreasing recombination losses in the studied devices, enhancing charge carrier lifetime. X-ray photoelectron spectroscopy measurements indicate the presence of a In and Se rich layer that we linked to be a KInSe2 layer. Our results suggest that when bulk and front interface recombination values are very high, they dominate and individual passivation strategies work poorly. Hence, this work shows that for ultrathin devices, passivation mitigation strategies need to be implemented in tandem.publishe

On the importance of joint mitigation strategies for front, bulk, and rear recombination in ultrathin Cu(In,Ga)Se2 solar cells

Several optoelectronic issues, such as poor optical absorption and recombination limit the power conversion efficiency of ultrathin Cu(In,Ga)Se2 (CIGS) solar cells. To mitigate recombination losses, two combined strategies were implemented: a Potassium Fluoride (KF) Post-Deposition Treatment (PDT) and a rear interface passivation strategy based on an Aluminium Oxide (Al2O3) point contact structure. The simultaneous implementation of both strategies is reported for the first time on ultrathin CIGS devices. Electrical measurements and 1-D simulations demonstrate that, in specific conditions, devices with only KF-PDT may outperform rear interface passivated based devices. By combining KF-PDT and rear interface passivation, an enhancement in open-circuit voltage of 178 mV is reached over devices that have a rear passivation only and of 85 mV over devices with only a KF-PDT process. Time-Resolved Photoluminescence measurements showed the beneficial effects of combining KF-PDT and the rear interface passivation at decreasing recombination losses in the studied devices, enhancing charge carrier lifetime. X-ray photoelectron spectroscopy measurements indicate the presence of a In and Se rich layer that we linked to be a KInSe2 layer. Our results suggest that when bulk and front interface recombination values are very high, they dominate and individual passivation strategies work poorly. Hence, this work shows that for ultrathin devices, passivation mitigation strategies need to be implemented in tandem.publishe

Encapsulation of Nanostructures in a Dielectric Matrix Providing Optical Enhancement in Ultrathin Solar Cells

The incorporation of nanostructures in optoelectronic devices for enhancing their optical performance is widely studied. However, several problems related to the processing complexity and the low performance of the nanostructures have hindered such actions in real-life devices. Herein, a novel way of introducing gold nanoparticles in a solar cell structure is proposed in which the nanostructures are encapsulated with a dielectric layer, shielding them from high temperatures and harsh growth processing conditions of the remaining device. Through optical simulations, an enhancement of the effective optical path length of approximately four times the nominal thickness of the absorber layer is verified with the new architecture. Furthermore, the proposed concept in a Cu(In,Ga)Se2 solar cell device is demonstrated, where the short-circuit current density is increased by 17.4%. The novel structure presented in this work is achieved by combining a bottom-up chemical approach of depositing the nanostructures with a top-down photolithographic process, which allows for an electrical contact.This work was funded in part by the Fundação para a Ciência e a Tecnologia (FCT) under Grants IF/00133/2015, PD/BD/142780/2018 and SFRH/BD/ 146776/2019. The authors also want to acknowledge the European Union’s Horizon 2020 Research and Innovation Programme through the ARCIGS-M project under Grant 720887, the Special Research Fund (BOF) of Hasselt University, the FCT through the project NovaCell (PTDC/CTM-CTM/28075/ 2017), and InovSolarCells (PTDC/FISMAC/29696/2017) co-funded by FCT and the ERDF through COMPETE2020. The authors also want to acknowledge Sandra Maya for the production of images used in this work.info:eu-repo/semantics/publishedVersio

Measurement of cortisol in saliva: a comparison of measurement error within and between international academic-research laboratories

Objective: Hundreds of scientific publications are produced annually that involve the measurement of cortisol in saliva. Intra- and inter-laboratory variation in salivary cortisol results has the potential to contribute to cross- study inconsistencies in findings, and the perception that salivary cortisol results are unreliable. This study rigor- ously estimates sources of measurement variability in the assay of salivary cortisol within and between established international academic-based laboratories that specialize in saliva analyses. One hundred young adults (Mean age: 23.10 years; 62 females) donated 2 mL of whole saliva by passive drool. Each sample was split into multiple- 100 µL aliquots and immediately frozen. One aliquot of each of the 100 participants’ saliva was transported to academic laboratories (N = 9) in the United States, Canada, UK, and Germany and assayed for cortisol by the same commercially available immunoassay. Results: 1.76% of the variance in salivary cortisol levels was attributable to differences between duplicate assays of the same sample within laboratories, 7.93% of the variance was associated with differences between laboratories, and 90.31% to differences between samples. In established-qualified laboratories, measurement error of salivary cortisol is minimal, and inter-laboratory differences in measurement are unlikely to have a major influence on the determined values