Seonju Jeong

Improved efficiency of bulk heterojunction poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester photovoltaic devices using discotic liquid crystal additives

Well established poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) bulk-heterojunction organic photovoltaics (BHJ OPVs) were improved by incorporating a small portion of the discotic liquid crystal (DLC) additives with a strong self-assembling ability and high mobility. Under simulated solar illumination of AM 1.5 (100 mW/cm2), the devices fabricated using P3HT:PC61BM (1:1.2 w:w) layer blended with 3 wt % of 2,3,6,7,10,11-hexaacetoxytriphenylene (DLC 2) achieved an average power conversion efficiency (PCE) of 3.97% after thermal annealing, compared to the reference cells with PCE=3.03%. DLCs have been proven here to be a promising new type of additive that can remain embedded in the active layer of high efficiency P3HT:PC61BM BHJ OPVs.

Au@polymer core-shell nanoparticles for simultaneously enhancing efficiency and ambient stability of organic optoelectronic devices.

In this paper, we report and discuss our successful synthesis of monodispersed, polystyrene-coated gold core-shell nanoparticles (Au@PS NPs) for use in highly efficient, air-stable, organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs). These core-shell NPs retain the dual functions of (1) the plasmonic effect of the Au core and (2) the stability and solvent resistance of the cross-linked PS shell. The monodispersed Au@PS NPs were incorporated into a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film that was located between the ITO substrate and the emitting layer (or active layer) in the devices. The incorporation of the Au@PS NPs provided remarkable improvements in the performances of both OLEDs and OPVs, which benefitted from the plasmonic effect of the Au@PS NPs. The OLED device with the Au@PS NPs achieved an enhancement of the current efficiency that was 42% greater than that of the control device. In addition, the power conversion efficiency was increased from 7.6% to 8.4% in PTB7:PC71BM-based OPVs when the Au@PS NPs were embedded. Direct evidence of the plasmonic effect on optical enhancement of the device was provided by near-field scanning optical microscopy measurements. More importantly, the Au@PS NPs induced a remarkable and simultaneous improvement in the stabilities of the OLED and OPV devices by reducing the acidic and hygroscopic properties of the PEDOT:PSS layer.

High-performance hybrid plastic films: a robust electrode platform for thin-film optoelectronics

We report a novel flexible hybrid plastic film that can be used as a robust electrode platform for typical thin-film optoelectronic devices. Silver nanowires (AgNWs) were embedded on the surface of a glass-fabric reinforced transparent composite (GFRHybrimer) film to form a flexible transparent conducting substrate with excellent opto-electrical properties, superior thermal stability, and impressive mechanical flexibility. A highly efficient and flexible inverted organic solar cell with a power conversion efficiency (PCE) of 5.9% under 100 mW cm−2 AM 1.5G illumination was fabricated on the AgNW–GFRHybrimer film. The AgNW–GFRHybrimer film exhibits potential as an excellent transparent electrode for low cost flexible optoelectronic devices.

Nanoimprinting-induced nanomorphological transition in polymer solar cells: enhanced electrical and optical performance.

We have investigated the effects of a directly nanopatterned active layer on the electrical and optical properties of inverted polymer solar cells (i-PSCs). The capillary force in confined molds plays a critical role in polymer crystallization and phase separation of the film. The nanoimprinting process induced improved crystallization and multidimensional chain alignment of polymers for more effective charge transfer and a fine phase-separation between polymers and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) to favor exciton dissociation and increase the generation rate of charge transfer excitons. Consequently, the power conversion efficiency with a periodic nanostructure was enhanced from 7.40% to 8.50% and 7.17% to 9.15% in PTB7 and PTB7-Th based i-PSCs, respectively.

Efficient light trapping in inverted polymer solar cells by a randomly nanostructured electrode using monodispersed polymer nanoparticles

The randomly nanotextured back electrode provides a simple and efficient route for enhancing photocurrent in polymer solar cells (PSCs) by light trapping, which can increase light absorption within a finite thickness of the active layer. In this study, we incorporated mono-disperse 60 nm polystyrene nanoparticles (PS NPs) into a 50 nm thick poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) anode buffer layer (ABL) to create a randomly nanotextured back electrode with 10 nm height variations in inverted-type PSCs. The roughened interface between the PS NP-PEDOT:PSS ABL and the Ag electrode scatters light in the visible range, leading to efficient light trapping within the device and enhanced light absorption in the active layer. Inverted PSCs with randomly nanotextured electrodes (φ(NP) = 0.31) showed short-circuit current density (J(SC)) and power conversion efficiency (PCE) values that were 15% higher than those of control devices with flat electrodes. External quantum efficiency, reflectance, and optical light scattering as a function of ϕ(NP) were examined to determine the origin of the enhancement in J(SC) and PCE.

Ultrafast formation of air-processable and high-quality polymer films on an aqueous substrate

Polymer solar cells are attracting attention as next-generation energy sources. Scalable deposition techniques of high-quality organic films should be guaranteed to realize highly efficient polymer solar cells in large areas for commercial viability. Herein, we introduce an ultrafast, scalable, and versatile process for forming high-quality organic films on an aqueous substrate by utilizing the spontaneous spreading phenomenon. This approach provides easy control over the thickness of the films by tuning the spreading conditions, and the films can be transferred to a variety of secondary substrates. Moreover, the controlled Marangoni flow and ultrafast removal of solvent during the process cause the films to have a uniform, high-quality nanomorphology with finely separated phase domains. Polymer solar cells were fabricated from a mixture of polymer and fullerene derivatives on an aqueous substrate by using the proposed technique, and the device exhibited an excellent power conversion efficiency of 8.44 %. Furthermore, a roll-to-roll production system was proposed as an air-processable and scalable commercial process for fabricating organic devices.

Synthesis and Electro-Optical Properties of 9,10-Substituted Anthracene Derivatives for Flexible OLED Devices

A silylated anthracene derivative, bis[2-(p-trimethylsilyl)phenylethynyl]anthracene (1), was synthesized by using Sonogashira reaction. Compound 1 showed two absorption maxia(λmax,abs) at 444 and 447 nm, and fluorescence maximum (λmax,em) at 478 nm. Compound 1 had higher melting temperature of 274°C compared to anthracene 210°C presumably due to confinement of π-conjugated system by trimethylsilyl end-capping, which will be beneficial in the high temperature operation condition of OLED devices. As compared to the commercially available, blue-light emitting, material 4 and tert-butylated compound 2, the compound 1 showed small red-shift of 9 nm in the OLED emission from the by PL λmax due to the increased electron density in the anthracene ring. The compound 1 was also found to be easily fabricated in the flexible OLED devices and showed a low threshold voltage and high current efficiency compared with other anthracene derivatives.

Bioinspired Transparent Laminated Composite Film for Flexible Green Optoelectronics

Herein, we report a new version of a bioinspired chitin nanofiber (ChNF) transparent laminated composite film (HCLaminate) made of siloxane hybrid materials (hybrimers) reinforced with ChNFs, which mimics the nanofiber-matrix structure of hierarchical biocomposites. Our HCLaminate is produced via vacuum bag compressing and subsequent UV-curing of the matrix resin-impregnated ChNF transparent paper (ChNF paper). It is worthwhile to note that this new type of ChNF-based transparent substrate film retains the strengths of the original ChNF paper and compensates for ChNF papers drawbacks as a flexible transparent substrate. As a result, compared with high-performance synthetic plastic films, such as poly(ethylene terephthalate), poly(ether sulfone), poly(ethylene naphthalate), and polyimide, our HCLaminate is characterized to exhibit extremely smooth surface topography, outstanding optical clarity, high elastic modulus, high dimensional stability, etc. To prove our HCLaminate as a substrate film, we use it to fabricate flexible perovskite solar cells and a touch-screen panel. As far as we know, this work is the first to demonstrate flexible optoelectronics, such as flexible perovskite solar cells and a touch-screen panel, actually fabricated on a composite film made of ChNF. Given its desirable macroscopic properties, we envision our HCLaminate being utilized as a transparent substrate film for flexible green optoelectronics.

Optical study of thin-film photovoltaic cells with apparent optical path length

Extending the insufficient optical path length (OPL) in thin-film photovoltaic cells (PVs) is the key to achieving a high power conversion efficiency (PCE) in devices. Here, we introduce the apparent OPL (AOPL) as a figure of merit for light absorbing capability in thin-film PVs. The optical characteristics such as the structural effects and angular responses in thin-film PVs were analyzed in terms of the AOPL. Although the Lambertian scattering surface yields a broadband absorption enhancement in thin-film PVs, the enhancement is not as effective as in thick-film PVs. On the other hand, nanophotonic schemes are introduced as an approach to increasing the single-pass AOPL by inducing surface plasmon resonance. The scheme using periodic metal gratings is proved to increase the AOPL in a narrow wavelength range and specific polarization, overcoming the Yablonovitch limit. The AOPL calculation can be also adopted in the experimental analysis and a maximum AOPL of 4.15d (where d is the active layer thickness) is exhibited in the absorption band edge region of PTB7:PC70BM-based polymer PVs.

Synthesis and Optical Properties of n-Type Polymers Containing Perylene Moieties

Three n-type polymers, Ppe01, Ppe02, and Ppe03, containing both perylene moieties and fluorine atoms were synthesized. The synthesiszed polymeric perylene derivatives with good compatibility for solution processes were chosen as new acceptor candidates for substitution of C60 derivatives in poly(3-hexylthiophene)-based organic photovoltaic application, by considering the results based on good thermal stability, high electron affinity ranging from 3.81 to 3.96 eV, absorption property in visible region, and effective photoluminescence quenching in the blend films with P3HT. The potential of the synthesized perylene polymers was investigated by measuring the current-voltage property of the polymeric P3HT: Ppe01 OPV device.