Unlocking the Potential of Colloidal Quantum Dot/Organic Hybrid Solar Cells: Band Tunable Interfacial Layer Approach.

Hybrid colloidal quantum dot (CQD)/organic architectures are promising candidates for emerging optoelectronic devices having high performance and inexpensive fabrication. For unlocking the potential of CQD/organic hybrid devices, enhancing charge extraction properties at electron transport layer (ETL)/CQD interfaces is crucial. Hence, we carefully adjust the interface properties between the ETL and CQD layer by incorporating an interfacial layer for the ETL (EIL) using several types of cinnamic acid ligands. The EIL having a cascading band offset (ΔEC) between the ETL and CQD layer suppresses the potential barrier and the local charge accumulation at ETL/CQD interfaces, thereby reducing the bimolecular recombination. An optimal EIL effectively expands the depletion region that facilitates charge extraction between the ETL and CQD layer while preventing the formation of shallow traps. Representative devices with an EIL exhibit a maximum power conversion efficiency of 14.01% and retain over 80% of initial performances after 300 h under continuous maximum power point operation.

Quantum Dot-Siloxane Anchoring on Colloidal Quantum Dot Film for Flexible Photovoltaic Cell.

Lead sulfide (PbS) colloidal quantum dots (CQDs) are promising materials for next-generation flexible solar cells because of near-infrared absorption, facile bandgap tunability, and superior air stability. However, CQD devices still lack enough flexibility to be applied to wearable devices owing to the poor mechanical properties of CQD films. In this study, a facile approach is proposed to improve the mechanical stability of CQDs solar cells without compromising the high power conversion efficiency (PCE) of the devices. (3-aminopropyl)triethoxysilane (APTS) is introduced on CQD films to strengthen the dot-to-dot bonding via QD-siloxane anchoring, and as a result, crack pattern analysis reveals that the treated devices become robust to mechanical stress. The device maintains 88% of the initial PCE under 12 000 cycles at a bending radius of 8.3 mm. In addition, APTS forms a dipole layer on CQD films, which improves the open circuit voltage (VOC ) of the device, achieving a PCE of 11.04%, one of the highest PCEs in flexible PbS CQD solar cells.

Association of Polymorphisms in FSHR, INHA, ESR1, and BMP15 with Recurrent Implantation Failure.

Recurrent implantation failure (RIF) refers to two or more unsuccessful in vitro fertilization embryo transfers in the same individual. Embryonic characteristics, immunological factors, and coagulation factors are known to be the causes of RIF. Genetic factors have also been reported to be involved in the occurrence of RIF, and some single nucleotide polymorphisms (SNPs) may contribute to RIF. We examined SNPs in FSHR, INHA, ESR1, and BMP15, which have been associated with primary ovarian failure. A cohort of 133 RIF patients and 317 healthy controls consisting of all Korean women was included. Genotyping was performed by Taq-Man genotyping assays to determine the frequency of the following polymorphisms: FSHR rs6165, INHA rs11893842 and rs35118453, ESR1 rs9340799 and rs2234693, and BMP15 rs17003221 and rs3810682. The differences in these SNPs were compared between the patient and control groups. Our results demonstrate a decreased prevalence of RIF in subjects with the FSHR rs6165 A>G polymorphism [AA vs. AG adjusted odds ratio (AOR) = 0.432; confidence interval (CI) = 0.206-0.908; p = 0.027, AA+AG vs. GG AOR = 0.434; CI = 0.213-0.885; p = 0.022]. Based on a genotype combination analysis, the GG/AA (FSHR rs6165/ESR1 rs9340799: OR = 0.250; CI = 0.072-0.874; p = 0.030) and GG-CC (FSHR rs6165/BMP15 rs3810682: OR = 0.466; CI = 0.220-0.987; p = 0.046) alleles were also associated with a decreased RIF risk. Additionally, the FSHR rs6165GG and BMP15 rs17003221TT+TC genotype combination was associated with a decreased RIF risk (OR = 0.430; CI = 0.210-0.877; p = 0.020) and increased FSH levels, as assessed by an analysis of variance. The FSHR rs6165 polymorphism and genotype combinations are significantly associated with RIF development in Korean women.

Corrosion behavior of silver-coated conductive yarn.

The corrosion mechanism and kinetics of the silver-coated conductive yarn (SCCY) used for wearable electronics were investigated under a NaCl solution, a main component of sweat. The corrosion occurs according to the mechanism in which silver reacts with chlorine ions to partly form sliver chloride on the surface of the SCCY and then the local silver chloride is detached into the electrolyte, leading to the electrical disconnect of the silver coating. Thus, the electrical conductance of the SCCY goes to zero after 2.7 h. The radial part-coating of gold, which is continuously electrodeposited in the longitudinal direction on the SCCY but is partly electrodeposited in the radial direction, extends the electrical conducting lifetime up to 192 h, despite the corrosion rate increasing from 129 to 196 mpy (mils per year). Results show that the gold partly-coating on the SCCY provides a current path for electrical conduction along the longitudinal direction until all the silver underneath the gold coating is detached from the SCCY strands, which creates the electrical disconnect. Based on the corrosion behavior, i.e., local oxidation and detachment of silver from the SCCY, the gold part-coating is more cost effective than the gold full-coating electrodeposited on the entire surface for electrically conducting SCCY.

Stretchable Electrodes Based on Over-Layered Liquid Metal Networks.

Liquid metals are attractive materials for stretchable electronics owing to their high electrical conductivity and near-zero Young's modulus. However, the high surface tension of liquid metals makes it difficult to form films. A novel stretchable film is proposed based on an over-layered liquid-metal network. An intentionally oxidized interfacial layer helps to construct uninterrupted indium and gallium nanoclusters and produces additional electrical pathways between the two metal networks under mechanical deformation. The films exhibit gigantic negative piezoresistivity (G-NPR), which decreased the resistance up to 85% during the first 50% stretching. This G-NPR property is due to the rupture of the metal oxides, which allows the formation of liquid eutectic gallium-indium (EGaIn) and the connection of the over-layered networks to build new electrical paths. The electrodes exhibiting G-NPR are complementarily combined with conventional electrodes to amplify their performance or achieve some unique operations.

Intrinsically Stretchable, Highly Efficient Organic Solar Cells Enabled by Polymer Donors Featuring Hydrogen-Bonding Spacers.

Intrinsically stretchable organic solar cells (IS-OSCs), consisting of all stretchable layers, are attracting significant attention as a future power source for wearable electronics. However, most of the efficient active layers for OSCs are mechanically brittle due to their rigid molecular structures designed for high electrical and optical properties. Here, a series of new polymer donors (PD s, PhAmX) featuring phenyl amide (N1 ,N3 -bis((5-bromothiophen-2-yl)methyl)isophthalamide, PhAm)-based flexible spacer (FS) inducing hydrogen-bonding (H-bonding) interactions is developed. These PD s enable IS-OSCs with a high power conversion efficiency (PCE) of 12.73% and excellent stretchability (PCE retention of >80% of the initial value at 32% strain), representing the best performances among the reported IS-OSCs to date. The incorporation of PhAm-based FS enhances the molecular ordering of PD s as well as their interactions with a Y7 acceptor, enhancing the mechanical stretchability and electrical properties simultaneously. It is also found that in rigid OSCs, the PhAm5:Y7 blend achieves a much higher PCE of 17.5% compared to that of the reference PM6:Y7 blend. The impact of the PhAm-FS linker on the mechanical and photovoltaic properties of OSCs is thoroughly investigated.

Material Design and Device Fabrication Strategies for Stretchable Organic Solar Cells.

Recent advances in the power conversion efficiency (PCE) of organic solar cells (OSCs) have greatly enhanced their commercial viability. Considering the technical standards (e.g., mechanical robustness) required for wearable electronics, which are promising application platforms for OSCs, the development of fully stretchable OSCs (f-SOSCs) should be accelerated. Here, a comprehensive overview of f-SOSCs, which are aimed to reliably operate under various forms of mechanical stress, including bending and multidirectional stretching, is provided. First, the mechanical requirements of f-SOSCs, in terms of tensile and cohesion/adhesion properties, are summarized along with the experimental methods to evaluate those properties. Second, essential studies to make each layer of f-SOSCs stretchable and efficient are discussed, emphasizing strategies to simultaneously enhance the photovoltaic and mechanical properties of the active layer, ranging from material design to fabrication control. Key improvements to the other components/layers (i.e., substrate, electrodes, and interlayers) are also covered. Lastly, considering that f-SOSC research is in its infancy, the current challenges and future prospects are explored.

All-in-One Process for Color Tuning and Patterning of Perovskite Quantum Dot Light-Emitting Diodes.

Although post-synthetic anion exchange allows halide perovskite quantum dots to easily change the optical bandgap of materials, additional exchange of shorter ligands is required to use them as active materials in optoelectronic devices. In this study, a novel all-in-one process exchanging ligands and halide anions in film-state for facile color tuning and patterning of cesium lead halide perovskite colloidal quantum dot (PeQD) light-emitting diodes (LEDs) is proposed. The proposed all-in-one process significantly enhances the performances of PeQD LEDs by passivating the PeQD with shorter ligands. In addition, the all-in-one process is repeated more stably in the film state. Red, green, and blue LEDs with extremely narrow emission spectra using cesium lead bromide PeQDs and appropriate butylammonium halide solutions are fabricated. Furthermore, the proposed all-in-one process in film-state facilitated rapid color change in localized areas, thereby aiding in realizing fine patterns of narrow widths (300 µm) using simple contact masks. Consequently, various paint-over red/green/blue patterns in PeQD LEDs by applying halide solutions additively are fabricated.

Highly Efficient Vacuum-Evaporated CsPbBr3 Perovskite Light-Emitting Diodes with an Electrical Conductivity Enhanced Polymer-Assisted Passivation Layer.

Highly efficient vacuum-deposited CsPbBr3 perovskite light-emitting diodes (PeLEDs) are demonstrated by introducing a separate polyethylene oxide (PEO) passivation layer. A CsPbBr3 film deposited on the PEO layer via thermal co-evaporation of CsBr and PbBr2 exhibits an almost 50-fold increase in photoluminescence quantum yield intensity compared to a reference sample without PEO. This enhancement is attributed to the passivation of interfacial defects of the perovskite, as evidenced by temperature-dependent photoluminescence measurements. However, direct application of PEO to an LED device is challenging because of the electrically insulating nature of PEO. This issue is solved by doping PEO layers with MgCl2. This strategy results in an enhanced luminance and external quantum efficiency (EQE) of up to 6887 cd m-2 and 7.6%, respectively. To the best of our knowledge, this is the highest EQE reported to date among vacuum-deposited PeLEDs.

Enhanced stretchability of metal/interlayer/metal hybrid electrode.

Despite the excellent electrical conductivity of metal thin film electrodes, their poor mechanical stretchability makes it extremely difficult to apply them as stretchable interconnect electrodes. Thus, we propose a novel stretchable hybrid electrode (SHE) by adopting two strategies to overcome the metal thin film electrode limitations: grain size engineering and hybridization with conductive interlayers. The grain size engineering technique improves the inherent metal thin film stretchability according to the Hall-Petch theory, and the hybridization of the conductive interlayer materials, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and carbon nanotube (CNT), suppresses crack propagation. Especially, the CNT-inserted SHE exhibits a decreased resistance change of approximately 32% in tensile test and 75% in a 10 000 cycle fatigue test because of the rough surface of the designed electrode, which relieves maximum stress by redistributing it more evenly to prevent penetrating crack propagation.

Role of Oxygen in Two-Step Thermal Annealing Processes for Enhancing the Performance of Colloidal Quantum Dot Solar Cells.

Colloidal quantum dots (CQDs) have large surface-to-volume ratios; thus, surface control is critical, especially when CQDs are utilized in optoelectronic devices. Layer-by-layer solid-state ligand exchange is a facile and applicable process for the formation of conductive CQD solids through various ligands; however, achieving complete ligand exchange on the CQD surface without dangling bonds is challenging. Herein, we demonstrate that CQDs can be further passivated through two-step annealing; air annealing forms sulfonate bonding at (111) Pb-rich surfaces, and subsequent N2 annealing removes insulating oxygen layers from the (100) surfaces of CQDs. By subsequently conducting annealing treatment in two different environments, traps on the surface of CQDs could be significantly reduced. We achieved a 40.8% enhancement of the power conversion efficiency by optimizing each two-step annealing process.

Chemo-Mechanically Operating Palladium-Polymer Nanograting Film for a Self-Powered H2 Gas Sensor.

This study proposes a reliable and self-powered hydrogen (H2) gas sensor composed of a chemo-mechanically operating nanostructured film and photovoltaic cell. Specifically, the nanostructured film has a configuration in which an asymmetrically coated palladium (Pd) film is coated on a periodic polyurethane acrylate (PUA) nanograting. The asymmetric Pd nanostructures, optimized by a finite element method simulation, swell upon reacting with H2 and thereby bend the PUA nanograting, changing the amount of transmitted light and the current output of the photovoltaic cell. Since the degree of warping is determined by the concentration of H2 gas, a wide concentration range of H2 (0.1-4.0%) can be detected by measuring the self-generated electrical current of the photovoltaic cell without external power. The normalized output current changes are ∼1.5%, ∼2.8%, ∼3.5%, ∼5.0%, ∼21.5%, and 25.3% when the concentrations of H2 gas are 0.1%, 0.5%, 1.0%, 1.6%, 2%, and 4%, respectively. Moreover, because Pd is highly chemically reactive to H2 and also because there is no electrical current applied through Pd, the proposed sensor can avoid device failure due to the breakage of the Pd sensing material, resulting in high reliability, and can show high selectivity against various gases such as carbon monoxide, hydrogen sulfide, nitrogen dioxide, and water vapor. Finally, using only ambient visible light, the sensor was modularized to produce an alarm in the presence of H2 gas, verifying a potential always-on H2 gas monitoring application.

Flexible Transparent Crystalline-ITO/Ag Nanowire Hybrid Electrode with High Stability for Organic Optoelectronics.

Metal nanowires (NWs) are promising transparent conducting electrode (TCE) materials because of their excellent optoelectrical performance, intrinsic mechanical flexibility, and large-scale processability. However, the surface roughness, thermal/chemical instability, and limited electrical conductivity associated with empty spaces between metal NWs are problems that are yet to be solved. Here, we report a highly reliable and robust composite TCE/substrate all-in-one platform that consists of crystalline indium tin oxide (c-ITO) top layer and surface-embedded metal NW (c-ITO/AgNW-GFRH) films for flexible optoelectronics. The c-ITO top layer (thickness: 10-30 nm) greatly improves the electrical performance of a AgNW-based electrode, retaining its transparency even after a high-temperature annealing process at 250 °C because of its thermally stable basal substrate (i.e., AgNW-GFRH). By introducing c-ITO thin film, we achieve an extremely smooth surface (Rrms < 1 nm), excellent optoelectrical performance, superior thermal (> 250 °C)/chemical stability (in sulfur-contained solution), and outstanding mechanical flexibility (bending radius = 1 mm). As a demonstration, we fabricate flexible organic devices (organic photovoltaic and organic light-emitting diode) on c-ITO/AgNW-GFRH films that show device performance comparable to that of references ITO/glass substrates and superior mechanical flexibility. With excellent stability and demonstrations, we expect that the c-ITO/AgNW-GFRHs can be used as flexible TCE/substrate films for future thin-film optoelectronics.

Self-Powered Gas Sensor Based on a Photovoltaic Cell and a Colorimetric Film with Hierarchical Micro/Nanostructures.

We report a new type of self-powered gas sensors based on the combination of a colorimetric film with hierarchical micro/nanostructures and organic photovoltaic cells. The transmittance of the colorimetric film with micro/nanostructures coated with N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD) changes by reacting with NO2 gas, and it is measured as a current output of the photovoltaic cell. For this purpose, materials for the organic photovoltaic cells were carefully chosen to match the working wavelength of the TMPD. Micropost arrays and nanowires increase the surface area for the gas reaction and thus improve the transmittance changes by NO2 gas (6.7% change for the plain film vs 27.7% change for the film with hierarchical micro/nanostructures to 20 ppm of NO2). Accordingly, the colorimetric device with the hierarchical structures showed a response of ΔI/I0 = 0.27-20 ppm of NO2, which is a 71% improvement compared to that of the plain sensing film. Furthermore, it showed a high selectivity against other gases such as H2S and CO with almost negligible responses. Since the current output change of the photovoltaic cell is utilized as a sensor signal, no extra electrical power is required for the operation of gas sensors. We also integrated the sensor device with an electrical module and demonstrated a self-powered gas alarm system.

Enhanced bendability of nanostructured metal electrodes: effect of nanoholes and their arrangement.

Metallic thin films often exhibit poor mechanical robustness, which makes them unsuitable for use as electrodes in flexible and stretchable electronic devices. This prompted us to investigate the effect of creating a pattern of nanoholes in a metallic thin film to its mechanical and electrical properties. The adoption of nanonetwork structures is shown to confer significantly improved bendability to the films, with a change in electrical resistance of only 21% after 10 000 bending cycles, under a bending strain of 6.3%. In contrast to the planar silver (Ag) films in which large cracks are formed, structures that contain nanoholes act as barriers that block the growth of cracks; consequently, only short cracks are formed in these films and therefore changes in their resistance are much lower. In this paper, we suggest a novel model based on random grain boundaries to simulate the behavior of various nanopattern arrangements when the film is subjected to mechanical stress. Our modeling studies revealed that nanoholes secure the electrical current pathways by effectively blocking crack propagation, and that optimizing orientation, size, and coverage of these nanoholes can further improve the mechanical properties. Although diamond patterns exhibit superior characteristics to those of rectangular ones, their directional dependence is shown to be reduced by adopting randomly dispersed nanostructures. We additionally verified experimentally that an array of holes (rectangular, diamond-shaped, and randomly patterned) significantly affects crack propagation and resistance change.

Flexible Bottom-Gated Organic Field-Effect Transistors Utilizing Stamped Polymer Layers from the Surface of Water.

The facile sequential deposition of functional organic thin films by solution processes is critical for the development of a variety of high-performance organic devices without restriction in terms of materials and processes. Herein, we propose a simple fabrication process that entails stacking multiple layers of functional polymers to fabricate organic field-effect transistors (OFETs). The process involves stamping organic semiconducting layers formed on the surface of water onto a commonly used polymeric dielectric layer. Our scheme makes it possible to independently optimize organic semiconductor films by controlling the solvent evaporation time during the process of film formation on the surface of water. This approach eliminates the need to be concerned about any interference with adjacent layers. Utilizing this process, the fabrication of high-performance bottom-gated OFETs is demonstrated on a glass and a flexible substrate. The OFETs consist of a vertically stacked diketopyrrolopyrrole-based polymer semiconducting layer on the poly(methyl methacrylate) film with a maximum hole mobility of 0.85 cm2/V s.

The role of photon recycling in perovskite light-emitting diodes.

Perovskite light-emitting diodes have recently broken the 20% barrier for external quantum efficiency. These values cannot be explained with classical models for optical outcoupling. Here, we analyse the role of photon recycling (PR) in assisting light extraction from perovskite light-emitting diodes. Spatially-resolved photoluminescence and electroluminescence measurements combined with optical modelling show that repetitive re-absorption and re-emission of photons trapped in substrate and waveguide modes significantly enhance light extraction when the radiation efficiency is sufficiently high. In this manner, PR can contribute more than 70% to the overall emission, in agreement with recently-reported high efficiencies. While an outcoupling efficiency of 100% is theoretically possible with PR, parasitic absorption losses due to absorption from the electrodes are shown to limit practical efficiencies in current device architectures. To overcome the present limits, we propose a future configuration with a reduced injection electrode area to drive the efficiency toward 100%.

Multi-bandgap Solar Energy Conversion via Combination of Microalgal Photosynthesis and Spectrally Selective Photovoltaic Cell.

Microalgal photosynthesis is a promising solar energy conversion process to produce high concentration biomass, which can be utilized in the various fields including bioenergy, food resources, and medicine. In this research, we study the optical design rule for microalgal cultivation systems, to efficiently utilize the solar energy and improve the photosynthesis efficiency. First, an organic luminescent dye of 3,6-Bis(4'-(diphenylamino)-1,1'-biphenyl-4-yl)-2,5-dihexyl-2,5-dihydropyrrolo3,4-c pyrrole -1,4-dione (D1) was coated on a photobioreactor (PBR) for microalgal cultivation. Unlike previous reports, there was no enhancement in the biomass productivities under artificial solar illuminations of 0.2 and 0.6 sun. We analyze the limitations and future design principles of the PBRs using photoluminescence under strong illumination. Second, as a multiple-bandgaps-scheme to maximize the conversion efficiency of solar energy, we propose a dual-energy generator that combines microalgal cultivation with spectrally selective photovoltaic cells (PVs). In the proposed system, the blue and green photons, of which high energy is not efficiently utilized in photosynthesis, are absorbed by a large-bandgap PV, generating electricity with a high open-circuit voltage (Voc) in reward for narrowing the absorption spectrum. Then, the unabsorbed red photons are guided into PBR and utilized for photosynthesis with high efficiency. Under an illumination of 7.2 kWh m-2 d-1, we experimentally verified that our dual-energy generator with C60-based PV can simultaneously produce 20.3 g m-2 d-1 of biomass and 220 Wh m-2 d-1 of electricity by utilizing multiple bandgaps in a single system.

Highly Efficient (>10%) Flexible Organic Solar Cells on PEDOT-Free and ITO-Free Transparent Electrodes.

A novel approach to fabricate flexible organic solar cells is proposed without indium tin oxide (ITO) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) using junction-free metal nanonetworks (NNs) as transparent electrodes. The metal NNs are monolithically etched using nanoscale shadow masks, and they exhibit excellent optoelectronic performance. Furthermore, the optoelectrical properties of the NNs can be controlled by both the initial metal layer thickness and NN density. Hence, with an extremely thin silver layer, the appropriate density control of the networks can lead to high transmittance and low sheet resistance. Such NNs can be utilized for thin-film devices without planarization by conductive materials such as PEDOT:PSS. A highly efficient flexible organic solar cell with a power conversion efficiency (PCE) of 10.6% and high device yield (93.8%) is fabricated on PEDOT-free and ITO-free transparent electrodes. Furthermore, the flexible solar cell retains 94.3% of the initial PCE even after 3000 bending stress tests (strain: 3.13%).

Study of Optical Configurations for Multiple Enhancement of Microalgal Biomass Production.

Microalga is a promising biomass feedstock to restore the global carbon balance and produce sustainable bioenergy. However, the present biomass productivity of microalgae is not high enough to be marketable mainly because of the inefficient utilization of solar energy. Here, we study optical engineering strategies to lead to a breakthrough in the biomass productivity and photosynthesis efficiency of a microalgae cultivation system. Our innovative optical system modelling reveals the theoretical potential (>100 g m-2 day-1) of the biomass productivity and it is used to compare the optical aspects of various photobioreactor designs previously proposed. Based on the optical analysis, the optimized V-shaped configuration experimentally demonstrates an enhancement of biomass productivity from 20.7 m-2 day-1 to 52.0 g m-2 day-1, under the solar-simulating illumination of 7.2 kWh m-2 day-1, through the dilution and trapping of incident energy. The importance of quantitative optical study for microalgal photosynthesis is clearly exhibited with practical demonstration of the doubled light utilization efficiencies.