Interfacial Engineering Importance of Bilayered ZnO Cathode Buffer on the Photovoltaic Performance of Inverted Organic Solar Cells

The role of cathode buffer layer (CBL) is crucial in determining the power conversion efficiency (PCE) of inverted organic solar cells (IOSCs). The hallmarks of a promising CBL include high transparency, ideal energy levels, and tendency to offer good interfacial contact with the organic bulk-heterojunction (BHJ) layers. Zinc oxide (ZnO), with its ability to form numerous morphologies in juxtaposition to its excellent electron affinity, solution processability, and good transparency is an ideal CBL material for IOSCs. Technically, when CBL is sandwiched between the BHJ active layer and the indium–tin-oxide (ITO) cathode, it performs two functions, namely, electron collection from the photoactive layer that is effectively carried out by morphologies like nanoparticles or nanoridges obtained by ZnO sol–gel (ZnO SG) method through an accumulation of individual nanoparticles and, second, transport of collected electrons toward the cathode, which is more effectively manifested by one-dimensional (1D) nanostructures like ZnO nanorods (ZnO NRs). This work presents the use of bilayered ZnO CBL in IOSCs of poly­(3-hexylthiophene) (P3HT)/[6, 6]-phenyl-C₆₀-butyric acid methyl ester (PCBM) to overcome the limitations offered by a conventionally used single layer CBL. We found that the PCE of IOSCs with an appropriate bilayer CBL comprising of ZnO NRs/ZnO SG is ∼18.21% higher than those containing ZnO SG/ZnO NRs. We believe that, in bilayer ZnO NRs/ZnO SG, ZnO SG collects electrons effectively from photoactive layer while ZnO NRs transport them further to ITO resulting significant increase in the photocurrent to achieve highest PCE of 3.70%. The enhancement in performance was obtained through improved interfacial engineering, enhanced electrical properties, and reduced surface/bulk defects in bilayer ZnO NRs/ZnO SG. This study demonstrates that the novel bilayer ZnO CBL approach of electron collection/transport would overcome crucial interfacial recombination issues and contribute in enhancing PCE of IOSCs

Flexible-wire shaped all-solid-state supercapacitors based on facile electropolymerization of polythiophene with ultra-high energy density

The new generation of miniaturized energy storage devices offers high energy and power densities and is compatible with flexible, portable, or wearable textile electronics which are currently in great demand. Here, we demonstrate the successful development of flexible, wire shaped (f-WS) all-solid-state symmetric supercapacitors (SCs) based on a facile electropolymerization of polythiophene (e-PTh) on titania (Ti) wire. The f-WS all-solid-state symmetric SCs, exhibiting high electrochemical performance, are fabricated by slightly intertwining two similar e-PTh electrodes to form both the cathode and anode which are then individually coated with a thin layer of H(2)SO(4)PVA gel, acting both as electrolyte and as separator. The optimized devices (similar to 1.5 cm long), based on e-PTh/Ti wire show a high capacitive performance (1357.31 mF g(-1) or 71.84 mF cm(-2)) and an extremely high energy density (23.11 mu W h cm(-2)) at a power density of 90.44 mu W cm-2 using an operational potential window of 1.8 V, which is beneficial for applications requiring high energy and power. The robust f-WS all-solid-state symmetric SCs also exhibit excellent mechanical flexibility with minimal change in capacitance upon bending at 360. Furthermore, the SCs were implemented in the textile of a wearable/portable electronic device using a conventional weaving method, thus demonstrating a high potential for next-generation wearable textile electronic applications

Co-functionalized organic/inorganic hybrid ZnO nanorods as electron transporting layers for inverted organic solar cells

In an unprecedented attempt, we present an interesting approach of coupling solution processed ZnO planar nanorods (NRs) by an organic small molecule (SM) with a strong electron withdrawing cyano moiety and the carboxylic group as binding sites by a facile co-functionalization approach. Direct functionalization by SMs (SM-ZnO NRs) leads to higher aggregation owing to the weaker solubility of SMs in solutions of ZnO NRs dispersed in chlorobenzene (CB). A prior addition of organic 2-(2-methoxyethoxy) acetic acid (MEA) over ZnO NRs not only inhibits aggregation of SMs over ZnO NRs, but also provides enough sites for the SM to strongly couple with the ZnO NRs to yield transparent SM-MEA-ZnO NRs hybrids that exhibited excellent capability as electron transporting layers (ETLs) in inverted organic solar cells (iOSCs) of P3HT:PC60BM bulk-heterojunction (BHJ) photoactive layers. A strongly coupled SM-MEA-ZnO NR hybrid reduces the series resistance by enhancing the interfacial area and tunes the energy level alignment at the interface between the (indium-doped tin oxide, ITO) cathode and BHJ photoactive layers. A significant enhancement in power conversion efficiency (PCE) was achieved for iOSCs comprising ETLs of SM-MEA-ZnO NRs (3.64%) advancing from 0.9% for pristine ZnO NRs, while the iOSCs of aggregated SM-ZnO NRs ETL exhibited a much lower PCE of 2.6%, thus demonstrating the potential of the co-functionalization approach. The superiority of the co-functionalized SM-MEA-ZnO NRs ETL is also evident from the highest PCE of 7.38% obtained for the iOSCs comprising BHJ of PTB7-Th: PC60BM compared with extremely poor 0.05% for non-functionalized ZnO NRsopen

Low-Temperature Solution-Processed SnO₂ Nanoparticles as a Cathode Buffer Layer for Inverted Organic Solar Cells

SnO₂ recently has attracted particular attention as a powerful buffer layer for organic optoelectronic devices due to its outstanding properties such as high electron mobility, suitable band alignment, and high optical transparency. Here, we report on facile low-temperature solution-processed SnO₂ nanoparticles (NPs) in applications for a cathode buffer layer (CBL) of inverted organic solar cells (iOSCs). The conduction band energy of SnO₂ NPs estimated by ultraviolet photoelectron spectroscopy was 4.01 eV, a salient feature that is necessary for an appropriate CBL. Using SnO₂ NPs as CBL derived from a 0.1 M precursor concentration, P3HT:PC₆₀BM-based iOSCs showed the best power conversion efficiency (PCE) of 2.9%. The iOSC devices using SnO₂ NPs as CBL revealed excellent long-term device stabilities, and the PCE was retained at ∼95% of its initial value after 10 weeks in ambient air. These solution-processed SnO₂ NPs are considered to be suitable for the low-cost, high throughput roll-to-roll process on a flexible substrate for optoelectronic devices

Controlled growth of polythiophene nanofibers in TiO2 nanotube arrays for supercapacitor applications

One-dimensional (1D) nanostructured materials have attracted intense interest because they are superior for applications when compared to their bulk counterparts, owing to their unique and fascinating properties. We thus demonstrate the development of conducting 1D polythiophene (PTh) nanofibers in hollow TiO2 nanotube arrays (TNTs) by controlling nucleation and growth during the electropolymerization of the thiophene monomer. The progression of nanofiber (NF) formation in the hollow interiors of the TNTs follows a three-dimensional instantaneous nucleation and growth mode, in which the polymer grows at a rate that does not allow for the build-up of the polymer on new polymerization sites, but only on existing ones. The formation of highly conductive dienes of PTh is confirmed, with increased conjugation in PTh NFs grown in the confined matrix of TNTs. These 1D PTh-TNT NFs show potential as a promising supercapacitor electrode material, exhibiting a high specific capacitance of 1052 F g(-1), which clearly highlights their importance as potential next-generation charge storage entities

Low-Temperature Solution-Processed Thiophene-Sulfur-Doped Planar ZnO Nanorods as Electron-Transporting Layers for Enhanced Performance of Organic Solar Cells

1-D ZnO represents a fascinating class of nanostructures that are significant to optoelectronics. In this work, we investigated the use of an eco-friendly, metal free in situ doping through a pure thiophene-sulfur (S) on low temperature processed (<95 °C) and annealed (<170 °C), planar 1-D ZnO nanorods (ZnRs) spin-coated as a hole-blocking and electron transporting layer (ETL) for inverted organic solar cells (<i>i</i>OSCs). The TEM, HRTEM, XPS, FT-IR, EDS and Raman studies clearly reveal that the thiophene-S (Thi-S) atom is incorporated on planar ZnRs. The investigations in electrical properties suggest the enhancement in conductivity after Thi-S doping on 1-D ZnRs. The <i>i</i>OSCs of poly­(3-hexylthiophene-2,5-diyl) and phenyl-C₆₁-butyric acid methyl ester (P3HT: PC₆₀BM) photoactive layer containing thiophene-S doped planar ZnRs (Thi-S-PZnRs) as ETL exhibits power conversion efficiency (PCE) of 3.68% under simulated AM 1.5 G, 100 mW cm^–2 illumination. The ∼47% enhancement in PCE compared with pristine planar ZnRs (PCE = 2.38%) ETL is attributed to a combination of desirable energy level alignment, morphological modification, increased conductivity and doping effect. The universality of Thi-S-PZnRs ETL is demonstrated by the highest PCE of 8.15% in contrast to 6.50% exhibited by the <i>i</i>OSCs of ZnRs ETL for the photoactive layer comprising of poly­[4,8-bis­(5-(2-ethylhexyl)­thiophene-2-yl)­benzo­[1,2-b;4,5-b]­dithiophene-2,6-diyl-<i>alt</i>-(4-(2-ethylhexyl)-3-fluorothieno­[3,4-<i>b</i>]­thiophene-)-2-carboxylate-2–6-diyl)]: phenyl-C71-butyric acid methyl ester (PTB7-Th: PCB₇₁M). This enhancement in PCE is observed to be driven mainly through improved photovoltaic parameters like fill factor (ff) as well as photocurrent density (<i>J</i>_sc), which are assigned to increased conductivity, exciton dissociation, and effective charge extraction, while; better ohmic contact, reduced charge recombination, and low leakage current density resulted in increased <i>V</i>_oc

Mechanical Behaviour, Contact Pose Estimation, and Finite Element Analysis of Vision Based Tactile Sensors Fabricated by Molding and Direct Ink Writing: A Comparative Study

Publication status: PublishedFunder: Advanced Research and innovation centerFunder: STRATA Manufacturing PJSC (a Mubadala company)Funder: Khalifa University of Science and Technology This work pioneers the application of direct ink writing (DIW) to fabricate elastomeric additively manufactured vision based tactile sensor (VBTS). DIW cuts down the fabrication time by 76%, allowing design precise control and reducing the complexities of the process compared to the state‐of‐the‐art (SOTA) molding techniques. Successful fabrication of DIW sensor is verified in three stages. Firstly, the mechanical characteristics of the DIW sensor are at par with those of SOTA molded Ecoflex in terms of depth of compression, compression rate, and the number of cycles. Secondly, using robotic pose estimation as a demonstration, the force enables deformation in the DIW sensor shows comparable normality estimation performance to that of the SOTA Ecoflex with a mean absolute error of less than 0.6°. Thirdly, finite element analysis (FEA) of DIW and SOTA Ecoflex sensors using Yeoh model shows similar stress and strain distributions as another evidence of DIW deformability and durability signaling sensor's successful fabrication.</jats:p

Nitrogen and Sulfur Co-Doped Carbon Quantum Dot-Engineered TiO₂ Graphene on Carbon Fabric for Photocatalysis Applications

Carbon quantum dots (CQDs) have gained considerable attention owing to their unique optoelectronic properties. However, these properties are quenched upon the aggregation of CQDs in solid-state devices, limiting their practical applications. Herein, we developed nitrogen and sulfur co-doped CQDs (NS-CQDs) by in situ carbonization process and were doped in TiO2-rGO (NS-CQDs-rGO-TiO2) nanocomposites on flexible carbon fabric substrate for efficient solid-state photocatalytic activity. The NS-CQDs-rGO-TiO2 photocatalyst decorated on flexible carbon fabric substrate facilitates recycling and thus improves the cycle life. The NS-CQD-rGO-TiO2 nanocomposites exhibited improved photocatalytic degradation of 98% toward organic pollutants (methylene blue dye) than conventional aggregation-induced quenching of N-doped CQDs-rGO-TiO2 (67%) under the same conditions. The enhanced photocatalytic activity of NS-CQD-rGO-TiO2 nanocomposites is ascribed to NS co-doping, ultrasmall nanoparticle morphology, mesoporous structure, high surface area, modified bandgap, the resulting mixed-phase TiO2, and formation of direct Z-scheme electron transfer under ultraviolet (UV) irradiation. Thus, this work provides insights into developing composite materials based on rutile TiO2 for photocatalytic environmental remediation

Improved Photoelectrochemical Cell Performance of Tin Oxide with Functionalized Multiwalled Carbon Nanotubes–Cadmium Selenide Sensitizer

Here we report functionalized multiwalled carbon nanotubes (<i>f</i>-MWCNTs)–CdSe nanocrystals (NCs) as photosensitizer in photoelectrochemical cells, where <i>f</i>-MWCNTs were uniformly coated with CdSe NCs onto SnO₂ upright standing nanosheets by using a simple electrodeposition method. The resultant blended photoanodes demonstrate extraordinary electrochemical properties including higher Stern–Volmer constant, higher absorbance, and positive quenching, etc., caused by more accessibility of CdSe NCs compared with pristine SnO₂–CdSe photoanode. Atomic and weight percent changes of carbon with <i>f</i>-MWCNTs blending concentrations were confirmed from the energy dispersive X-ray analysis. The morphology images show a uniform coverage of CdSe NCs over <i>f</i>-MWCNTs forming a core–shell type structure as a blend. Compared to pristine CdSe, photoanode with <i>f</i>-MWCNTs demonstrated a 257% increase in overall power conversion efficiency. Obtained results were corroborated by the electrochemical impedance analysis. Higher scattering, more accessibility, and hierarchical structure of SnO₂-<i>f</i>-MWCNTs-blend–CdSe NCs photoanode is responsible for higher (a) electron mobility (6.89 × 10^–4 to 10.89 × 10^–4 cm² V^–1 S^1–), (b) diffusion length (27 × 10^–6), (c) average electron lifetime (32.2 ms), and transit time (1.15 ms)