Ultrathin a-Si:H/Oxide transparent solar cells exhibiting UV-Blue selective-like absorption

This is the peer reviewed version of the following article: Lopez-Garcia, A. [et al.]. Ultrathin a-Si:H/Oxide transparent solar cells exhibiting UV-Blue selective-like absorption. "Solar RRL", April 2023, which has been published in final form at https://onlinelibrary.wiley.com/doi/10.1002/solr.202200928. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.Herein, the fabrication of transparent solar cells based on nanometric (8 and30 nm) intrinsic hydrogenated amorphous siliconfilms (a-Si:H) and using oxidethinfilms as transparent carrier selective contacts are reported. The ultrathindevices present photovoltaic effect and high average visible transmittance (AVT).Additionally, they display a shifted spectral response toward short wavelengths.Glass/fluorine-doped tin oxide (FTO)/aluminum-doped zinc oxide (AZO)/a-Si:H/MoO3/indium tin oxide (ITO) prototypes are shown, presenting AVT=35% andphotovoltaic conversion efficiency (PCE)=2% for a device with a 30 nm a-Si:Hfilm. This yields a light utilization efficiency (LUE) of 0.7%, a record up to this datefor inorganic oxide-based transparent solar cells. For devices including an 8 nma-Si:Hfilm, the AVT reaches 66% with a PCE=0.6% (LUE=0.4%). These highAVT values are comparable or even superior in some cases to those achieved forpure oxide devices. Thesefindings confirm the potential of the proposedarchitectures for the development of highly transparent energy harvesters asfunctional components in building-integrated photovoltaics (BIPV), agrophoto-voltaics (APV), sensors and other low-power devices. In addition, these devicesare fabricated with earth-abundant materials and with up-scalable techniquesthat can allow for a feasible implementation.Peer ReviewedPostprint (published version

2-step process for 5.4% CuGaSe2 solar cell using fluorine doped tin oxide transparent back contacts

As single-junction solar cells are approaching theoretical limits, multijunction solar cells are becoming increasingly relevant, and low-cost wider bandgap light harvesters in tandem with silicon are the next frontier in thin film photovoltaic research. Cu-based chalcogenide compounds have achieved great success as standard absorbers, but performance for bandgaps above 1.5¿eV is still lacking. Additionally, the use of transparent back contacts remains challenging for this class of materials. In this work, we report on the fabrication of wide bandgap CuGaSe2 absorbers by a combination of metallic sputtering and reactive thermal annealing grown on transparent fluorine-doped tin oxide-coated glass substrate. The annealing temperature is carefully tuned in regard to material and photovoltaic device properties. The introduction of an ultrathin Mo interlayer at the CuGaSe2/back interface favors a higher contact's ohmicity and results in an important improvement of all figures of merit. A record conversion efficiency of 5.4% is obtained, which is the highest value reported for this class of absorber on transparent back contact. Fundamental material characterization of the as-grown CuGaSe2 films reveals a better homogeneity in Cu distribution throughout the absorber's thickness when using a Mo interlayer, along with an enhanced crystalline quality. The sub-bandgap transparency of the final device remains perfectible, and improvement pathways are proposed using transfer matrix-based optical modeling, suggesting to use more specular interfaces to enhance optical transmission.Peer ReviewedPostprint (published version

Characterization of the stability of indium tin oxide and functional layers for semitransparent back-contact applications on Cu(in,Ga)Se2 solar cells

Herein, a detailed study of the stability of different ITO-based back-contact configurations (including bare ITO contacts and contacts functionalized with nanometric Mo, MoSe2, and MoS2 layers) under the coevaporation processes developed for the synthesis of high-efficiency Cu(In,Ga)Se2 (CIGSe) solar cells is reported. The results show that bare ITO layers can be used as efficient back contacts for coevaporation process temperatures of 480¿ºC. However, higher temperatures produce an amorphous In–Se phase at the ITO surface that reduces the contacts transparency in the visible region. This is accompanied by degradation of the solar cells’ efficiency. Inclusion of a Mo functional layer leads to the formation of a MoSe2 interfacial phase during the coevaporation process, which improves the cells’ efficiency, achieving device efficiencies similar to those obtained with reference solar cells fabricated with standard Mo back contacts. Optimization of the initial Mo layer thickness improves the contact transparency, achieving contacts with an optical transparency of 50% in the visible region. This is accompanied by a relevant decrease in back reflectivity in the CIGSe devices, confirming the potential of these contact configurations for the development of semitransparent CIGSe devices with improved optical aesthetic quality without compromising the device performance.Peer ReviewedPostprint (published version

A new approach for alkali incorporation in Cu2ZnSnS4 solar cells

The addition of alkali elements has become mandatory for boosting solar cell performance in chalcogenide thin films based on kesterites (Cu2ZnSnS4, CZTS). A novel doping process is presented here, that consists in the incorporation of sodium or lithium during the deposition of the CdS buffer layer, followed by a post-deposition annealing (PDA). As the doping route leads to more efficient devices in comparison with the undoped reference sample, the influence of PDA temperature was also investigated. Compositional profiling techniques, time-of-flight secondary ion mass spectrometry (TOF-SIMS) and glow discharge optical mission spectroscopy (GDOES), revealed a dependence of the alkaline distribution in kesterites with the PDA temperature. Although the doping process is effective in that it increases the alkaline concentration compared to the undoped sample, the compositional profiles indicate that a significant proportion of Li and Na remains 'trapped' within the CdS layer. In the 200 °C–300 °C range the alkali profiles registered the higher concentration inside the kesterite. Despite this, an additional alkali accumulation close to the molybdenum/fluorine doped tin oxide substrate was found for all the samples, which is frequently related to alkali segregation at interfaces. The addition of both, lithium and sodium, improves the photovoltaic response compared to the undoped reference device. This is mainly explained by a substantial improvement in the open-circuit potential (Voc) of the cells, with best devices achieving efficiencies of 4.5% and 3% for lithium and sodium, respectively. Scanning-electron microscopy images depicted a 'bilayer structure' with larger grains at the top and small grains at the bottom in all samples. Moreover, the calculated bandgap energies of the CZTS films account for changes in the crystallographic order-disorder of the kesterites, more related to the PDA treatment rather than alkali incorporation. Even if further optimization of the absorber synthesis and doping process will be required, this investigation allowed the evaluation of a novel strategy for alkali incorporation in kesterite based solar cells.Peer ReviewedPostprint (published version

Insights into interface and bulk defects in a high efficiency kesterite-based device

This work provides a detailed analysis of a high efficiency Cu2ZnSnSe4 device using a combination of advanced electron microscopy and spectroscopy techniques. In particular, a full picture of the different defects present at the interfaces of the device and in the bulk of the absorber is achieved through the combination of high resolution electron microscopy techniques with Raman, X-ray fluorescence and Auger spectroscopy measurements at the macro, micro and nano scales. The simultaneous investigation of the bulk and the interfaces allows assessing the impact of the defects found in each part of the device on its performance. Despite a good crystalline quality and homogeneous composition in the bulk, this work reports, for the first time, direct evidence of twinning defects in the bulk, of micro and nano-voids at the back interface and of grain-to-grain non-uniformities and dislocation defects at the front interface. These, together with other issues observed such as strong absorber thickness variations and a bilayer structure with small grains at the bottom, are shown to be the main factors limiting the performance of CZTSe devices. These results open the way to the identification of new solutions to further developing the kesterite technology and pushing it towards higher performances. Moreover, this study provides an example of how the advanced characterization of emergent multilayer-based devices can be employed to elucidate their main limitations.Peer ReviewedPostprint (author's final draft

Does Sb2Se3 admit nonstoichiometric conditions? How modifying the overall se content affects the structural, optical, and optoelectronic properties of Sb2Se3 thin films

Sb2Se3 is a quasi-one-dimensional (1D) semiconductor, which has shown great promise in photovoltaics. However, its performance is currently limited by a high Voc deficit. Therefore, it is necessary to explore new strategies to minimize the formation of intrinsic defects and thus unlock the absorber’s whole potential. It has been reported that tuning the Se/Sb relative content could enable a selective control of the defects. Furthermore, recent experimental evidence has shown that moderate Se excess enhances the photovoltaic performance; however, it is not yet clear whether this excess has been incorporated into the structure. In this work, a series of Sb2Se3 thin films have been prepared imposing different nominal compositions (from Sb-rich to Se-rich) and then have been thoroughly characterized using compositional, structural, and optical analysis techniques. Hence, it is shown that Sb2Se3 does not allow an extended range of nonstoichiometric conditions. Instead, any Sb or Se excesses are compensated in the form of secondary phases. Also, a correlation has been found between operating under Se-rich conditions and an improvement in the crystalline orientation, which is likely related to the formation of a MoSe2 phase in the back interface. Finally, this study shows new utilities of Raman, X-ray diffraction, and photothermal deflection spectroscopy combination techniques to examine the structural properties of Sb2Se3, especially how well-oriented the material is.Postprint (published version

Challenges and improvement pathways to develop quasi-1D (Sb1-xBix)2Se3-based materials for optically tuneable photovoltaic applications. Towards chalcogenide narrow-bandgap devices

Quasi-1D chalcogenides have shown great promises in the development of emerging photovoltaic technologies. However, most quasi-1D semiconductors other than Sb2Se3 and Sb2S3 have been seldom investigated for energy generation applications. Indeed, cationic or anionic alloying strategies allow changing the bandgap of these materials, opening the door to the development of an extended range of chalcogenides with tuneable optical and electrical properties. In this work, Bi incorporation into the Sb2Se3 structure has been proved as an effective approach to modulate the bandgap between 0.1. In order to better understand the underlying mechanisms leading to the formation of (Sb1-xBix)2Se3, and thus design specific strategies to enhance its properties, thin films with different annealing time and temperature have been synthesized and characterized. Interestingly, it has been observed that Sb2Se3 and Bi2Se3 are formed first, with Bi melting at 300 ¿C and diffusing rapidly towards the surface of the film. At higher temperature, the binary compounds combine to form the solid solution, however as the dwell time increases, (Sb1-xBix)2Se3 decomposes again into Bi2Se3 and Sb. This study has shown that the material is essentially limited by compositional disorder and recombination via defects. Likewise, routes have been proposed to improve morphology and uniformity of the layer, achieving efficiencies higher than 1% for x > 0.2Postprint (published version

Protection against reinfection with D614- or G614-SARS-CoV-2 isolates in golden Syrian hamster

Reinfections with SARS-CoV-2 have already been documented in humans, although its real incidence is currently unknown. Besides having a great impact on public health, this phenomenon raises the question of immunity generated by a single infection is sufficient to provide sterilizing/protective immunity to a subsequent SARS-CoV-2 re-exposure. The Golden Syrian hamster is a manageable animal model to explore immunological mechanisms able to counteract COVID-19, as it recapitulates pathological aspects of mild to moderately affected patients. Here, we report that SARS-CoV-2-inoculated hamsters resolve infection in the upper and lower respiratory tracts within seven days upon inoculation with the Cat01 (G614) SARS-CoV-2 isolate. Three weeks after the primary challenge, and despite high titres of neutralizing antibodies, half of the animals were susceptible to reinfection by both identical (Cat01, G614) and variant (WA/1, D614) SARS-CoV-2 isolates. However, upon re-inoculation, only nasal tissues were transiently infected with much lower viral replication than those observed after the first inoculation. These data indicate that a primary SARS-CoV-2 infection is not sufficient to elicit a sterilizing immunity in hamster models but protects against lung disease.info:eu-repo/semantics/publishedVersio

Role of age and comorbidities in mortality of patients with infective endocarditis

[Purpose]: The aim of this study was to analyse the characteristics of patients with IE in three groups of age and to assess the ability of age and the Charlson Comorbidity Index (CCI) to predict mortality. [Methods]: Prospective cohort study of all patients with IE included in the GAMES Spanish database between 2008 and 2015.Patients were stratified into three age groups:<65 years,65 to 80 years,and ≥ 80 years.The area under the receiver-operating characteristic (AUROC) curve was calculated to quantify the diagnostic accuracy of the CCI to predict mortality risk. [Results]: A total of 3120 patients with IE (1327 < 65 years;1291 65-80 years;502 ≥ 80 years) were enrolled.Fever and heart failure were the most common presentations of IE, with no differences among age groups.Patients ≥80 years who underwent surgery were significantly lower compared with other age groups (14.3%,65 years; 20.5%,65-79 years; 31.3%,≥80 years). In-hospital mortality was lower in the <65-year group (20.3%,<65 years;30.1%,65-79 years;34.7%,≥80 years;p < 0.001) as well as 1-year mortality (3.2%, <65 years; 5.5%, 65-80 years;7.6%,≥80 years; p = 0.003).Independent predictors of mortality were age ≥ 80 years (hazard ratio [HR]:2.78;95% confidence interval [CI]:2.32–3.34), CCI ≥ 3 (HR:1.62; 95% CI:1.39–1.88),and non-performed surgery (HR:1.64;95% CI:11.16–1.58).When the three age groups were compared,the AUROC curve for CCI was significantly larger for patients aged <65 years(p < 0.001) for both in-hospital and 1-year mortality. [Conclusion]: There were no differences in the clinical presentation of IE between the groups. Age ≥ 80 years, high comorbidity (measured by CCI),and non-performance of surgery were independent predictors of mortality in patients with IE.CCI could help to identify those patients with IE and surgical indication who present a lower risk of in-hospital and 1-year mortality after surgery, especially in the <65-year group

Ultrathin wide-bandgap a-Si:H-based solar cells for transparent photovoltaic applications

This is the peer reviewed version of the following article: Lopez-Garcia, A. [et al.]. Ultrathin wide-bandgap a-Si:H-based solar cells for transparent photovoltaic applications. "Solar RRL", 1 Gener 2022, vol. 6, núm. 1, p. 2100909:1-2100909:8. , which has been published in final form at https://onlinelibrary.wiley.com/doi/full/10.1002/solr.202100909. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.Herein, the fabrication of UV-blue selective transparent solar cells based on ultrathin (<30¿nm) intrinsic hydrogenated amorphous silicon films (a-Si:H) as absorber and using a fully inorganic architecture is reported, using metal-oxide thin films as carrier selective contacts and as transparent electrical contacts. These transparent ultrathin devices present a photovoltaic effect and high average visible transmittance (AVT), showing their potential as candidates for implementation as a transparent energy harvester. Potential applications range from Building-Integrated PV to agrophotovoltaics, and can also be of interest as a ubiquitous and inexpensive power source integrated in functional devices such as low-power devices, Internet of Things devices, and other sensors. Glass/FTO/ZnO/a-Si:H/MoO3/ITO device prototypes are produced. These devices present an AVT ranging from 50% to 69%, present a photovoltaic effect with a power conversion efficiency up to 0.5% calculated for an AM1.5G spectrum and have light utilization efficiency (LUE) values of 0.25%, confirming the potential of the proposed device architectures for the development of highly transparent devices with improved LUE.This work has received funding from the European Union H2020Framework Programme under Grant Agreement no. 826002(Tech4Win). This work is also part of the RþDþi MaterOne projects(Refs. PID 2020-116719RB-C42 and PID 2020-116719RB-C41) and ofthe RþDþi SCALED project (Ref. PID 2019-109215RB-C4) funded byMCIN/AEI/10.13039/5011000110033. Authors from IREC andUniversitat de Barcelona belong to the SEMS (Solar Energy Materialsand Systems) Consolidated Research Group of the“Generalitat deCatalunya”(Ref. 2017 SGR 862).Peer ReviewedPostprint (published version