Sungho Woo

Daegu Gyeongbuk Institute of Science and Technology | DGIST · Green Energy Research Division

All-inorganic metal halide perovskite nanocrystals (IPeNCs) have become one of the most promising luminescent materials for next-generation display and lighting technology owing to their excellent color expression ability. However, research on IPeNCs with stable blue emission is limited. In this paper, we report stable blue emissive all-bromide IPe...

CsPbIBr2, a cesium-based all-inorganic halide perovskite (CsPe), is a very promising alternative material to mainstream organic–inorganic hybrid halide perovskite (HPe) materials owing to its exceptional moisture stability, thermal stability, and light stability. However, because of the wide band gap (2.05 eV) of CsPbIBr2, it has a low power conver...

CsPbIBr 2 , a type of cesium based all-inorganic halide perovskite (CsPe) composition, has been proposed as an alternative perovskite material against the mainstream organic–inorganic hybrid halide perovskite (HPe) materials owing to its exceptional humidity, thermal, temperature, and light stability. However, the low power conversion efficiency (...

We report a highly effective surface treatment method for planar-type Sb2S3 solar cells by employing a Cs2CO3-modified compact TiO2 (c-TiO2) electron transport layer. It is found that surface treatment using a Cs2CO3 solution can shift the work function of c-TiO2 upward and reduce its surface roughness. As a result, compared with the power conversi...

The Ag nanowire (NW) + Au nanoparticle (NP)-embedded TiO2 photoelectrodes were adopted for conventional planar TiO2-based Sb2S3 hybrid solar cells to improve the cell efficiency. Compared to conventional planar TiO2-based Sb2S3 hybrid solar cells, the Ag NW + Au NP/TiO2-based Sb2S3 hybrid solar cells exhibited an improvement of approximately 40% in...

In this study, we optimized the electrolyte components with different composition and additives on the performance of new metal-free organic dye-sensitized solar cells. The liquid electrolyte consisted of iodine (I2, lithium iodide (LiI), guanidinium thiocyanate (GuSCN) and 1-methyl-3-propylimidazolium iodide (MPII) or 1,2-dimethyl-3-propylimidazol...

We adopted Ag nanowire (NW)/ZnO core–shell photoelectrodes for conventional planar ZnO-based Sb2S3 hybrid solar cells to improve the cell efficiency. The core–shell structure consisted of a network of Ag NWs as the core and a ZnO shell in the form of a coating layer covering the surface of the Ag NWs Compared to conventional planar ZnO-based Sb2S3...

Polymer solar cells have been spotlighted due to their potential for low-cost manufacturing but their efficiency is still less than required for commercial application as lightweight/flexible modules. Forming a dipole layer at the electron-collecting interface has been suggested as one of the more attractive approaches for efficiency enhancement. H...

Supplementary Figures 1-7, Supplementary Table 1 and Supplementary References.

The performance of solar cells with a polymer:polymer bulk heterojunction (BHJ) structure, consisting of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b']dithiophene-alt-3-fluorothieno[3,4-b]thiophene-2-carboxylate] (PTB7-Th) donor and poly[[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithio...

The efficiency of polymer solar cells (PSCs) with P3HT [poly(3-hexyl thiophene)]:PC61BM [[6,6]-phenyl C61-butyric acid methyl ester] blend film was improved by the incorporation of a fluorocyanophenyl compound, 3,4,5,6-tetrafluorophthalonitrile (TFP), as an additive. When the amount of TFT additive was 5 wt% based on the total amount of P3HT and PC...

Poly(diallyldimethylammonium chloride) (PDAC), a water-soluble polyelectrolyte, is used as the electron collecting layer (ECL) on indium tin oxide (ITO) for inverted polymer solar cells (PSCs) with poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C71-butyric acid methyl ester (PC71 BM) as the active materials. PDAC is coated directly on top of the IT...

A micro-engraved bulk heterojunction (BHJ) nanolayer, which is formed by pressing with a micrometer-scale embossed metal mold, was introduced to fabricate polymer:fullerene solar cells. The embossed metal molds with three different pattern sizes were fabricated by employing a typical lithography/etching process. After the embossed metal molds were...

A phenyl compound with electron withdrawing substituents, 3-fluoro-4-cyanophenol (FCP), was used as an additive in polymer solar cells with a P3HT [poly(3-hexyl thiophene)]:PCBM [[6,6]-phenyl-C61-butyric acid methyl ester] blend film. Under simulated solar illumination of AM 1.5 (100 mW/cm2), the devices fabricated using a P3HT:PCBM (1:0.9 w:w) lay...

Enhanced power conversion efficiency (PCE) is reported in inverted polymer solar cells when an electron-rich polymer nanolayer (poly(ethyleneimine) (PEI)) is placed on the surface of an electron-collecting buffer layer (ZnO). The active layer is made with bulk heterojunction films of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,...

Here we report new low-cost nanocomposite counter electrodes for dye-sensitized solar cells (DSSCs), which were prepared by in-situ generation of platinum (Pt) nanoparticles inside poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solutions at room temperature. The Pt nanoparticles (Ptnp) were evenly dispersed in the PEDOT:PSS fil...

Here we report the wide range thickness effect of hole-collecting buffer layers (poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS)) on the performance of polymer:fullerene solar cells with blend films of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM). The thickness of the PEDOT:PSS layers w...

In this work, we report on the enhanced power conversion efficiency (PCE) of inverted polymer solar cells (I-PSCs) that use a surface treatment of ZnO electron transporting layer by benzoic acid derivatives. A thin SAM layers of 4-methoxybenzoic acid (mBA) or 4'-methoxybiphenyl-4-carboxylic acid (mBPCA), prepared by spin-coating, on top of ZnO, was...

The performance of poly(3-hexylthiophen) (P3HT) and [6, 6]phenyl C61 butyric acid methyl ester ([60]PCBM)-based inverted bulk-heterojunction (BHJ) polymer solar cells (PSCs) is enhanced by the modification of zinc oxide (ZnO)/BHJ interface with carboxylic-acid-functionalized self-assembled monolayers (SAMs). Under simulated solar illumination of AM...

Here, the improved performance of organic field effect transistors (OFET) by doping inorganic nanoparticles into a semiconducting polymer as a channel layer is briefly reported. Nickel(II) oxide nanoparticle (NiOnp) was used as an inorganic dopant while regioregular poly(3-hexylthiophene) (P3HT) was used as a matrix polymer for the channel layer in...

We investigated optical properties of subwavelength patterned metal gratings for photonic device application. It was known that optical transmittance of metal films with subwavelength periodic hole arrays can be controlled by applying a dielectric overlay to the film and the films can act as wavelength or frequency selective filters. Following adva...

Here we report the influences of the sheet resistance () of a hole-collecting electrode (indium tin oxide, ITO) and the conductivity of a hole-collecting buffer layer (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS) on the device performance of flexible plastic organic photovoltaic (OPV) devices. The series resistance () of OPV...

We report an enhancement in the efficiency of organic solar cells via the incorporation of gold (Au) or silver (Ag) nanoparticles (NPs) in the hole-transporting buffer layer of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), which was formed on an indium tin oxide (ITO) surface by the spin-coating of PEDOT:PSS-Au or Ag NPs comp...

Lead sulfide (PbS) nanoparticles were generated by the in-situ reaction of lead chloride (II) and sulfur in the presence of poly (3-hexylthiophene) (P3HT) dissolved in the co-solvents. Three different reaction times were used to examine the effect of the PbS reaction conditions. The in-situ generated PbS nanoparticles in the P3HT matrix were spheri...

We report a diimide-type organic electron-injecting material, bis-[1,10]phenanthrolin-5-yl-pyromellitic diimide (Bphen-PMDI), for organic light-emitting devices (OLEDs), which was synthesized from its monomers, pyromellitic dianhydride (PMDA) and 1,10-phenanthrolin-5-amine (PTA). The vacuum-purified Bphen-PMDI powder showed high glass transition (2...

Organic/inorganic hybrid solar cells, based on vertically aligned n-type silicon nanowires (n-Si NWs) and p-type conducting polymers (PEDOT:PSS), were investigated as a function of Si conductivity. The n-Si NWs were easily prepared from the n-Si wafer by employing a silver nanodot-mediated micro-electrochemical redox reaction. This investigation sh...

We investigated the influence of nickel oxide (NiO) nanoparticles that are incorporated into the hole-collecting buffer layer [poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)] on the performance of polymer:fullerene solar cells. To understand the optimum composition of NiO nanoparticles, the composition of NiO nanoparticles was...

The synthesized n-type perylene derivative, N,N'-bis-(4-bromophenyl)-1,6,7,12-tetrakis(4-n-butoxy-phenoxy)-3,4,9,10-perylene tetracarboxdiimide (PIBr), was applied as an additive to polymer solar cells (PSCs) with P3HT [poly(3-hexylthiophene)]:PCBM [[6,6]-phenyl C61-butyric acid methyl ester] blend films. Without post thermal annealing, a considera...

To enhance the performance and understanding of organic photovoltaic devices (OPVs), we have investigated the influence of organic solar cell geometry on power loss and device efficiency using three-dimensional finite element (3-D FE) simulation. To investigate the influence of geometry on power loss, we have proposed a new simple finite element (F...

We report an experimental optimization of the cleaning process in the fabrication of flexible polymer solar cells using an indium tin oxide (ITO) coated poly(ethylene naphthalate) (PEN) substrate. The effects of the solubility parameters of the cleaning solvents on the occurrence of ITO cracks have been systematically investigated. The experimental...

In this study, the influence of an active cell design on the power conversion efficiency (PCE) of a monolithic organic photovoltaic (OPV) module was investigated using experimental methods and circuit simulation. For circuit simulation using computer simulation-based study, the organic PV cell was described by a circuit-based two-diode model and th...

For efficiency enhancement of a large-area monolithic organic photovoltaic (OPV) module, we studied the influence of the OPV cell geometry parameters using theoretical and experimental methods. For this work, a unit OPV cell as a reference device and four types of monolithic OPV module with different active cell lengths were fabricated together on...

In this work, 4-fluorobenzonitrile (4-FBN) was introduced as a new additive compound into the photoactive layer of a polymer solar cell (PSC) based on a poly(3-hexylthiophene):[6,6]-phenyl-C 61- butyric acid methyl ester (P3HT:PCBM) blend system. The incorporation of 4-FBN allowed both increased light absorption (φ-φ* transition efficiency) in the...

A perfluorinated compound, 4-amino-2-(trifluoromethyl)benzonitrile (ATMB), was applied as an additive to polymer solar cells (PSCs) with P3HT [poly(3-hexylthiophene)]:PCBM [[6,6]-phenyl-C61-butyric acid methyl ester] blend films. The addition of 6wt% ATMB to a P3HT:PCBM layer led to an increased power conversion efficiency of 5.03% due to the enhan...

We report the influence of the controlled acidity of the hole-collecting buffer layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), on the performance and lifetime of polymer:fullerene solar cells. The acidity was controlled by adding a strong base (NaOH) to the pristine PEDOT:PSS solutions. The NaOH-modified PEDOT:PSS layer...

In order to protect human lives from disease, various biosensors having the potential to analyze a variety of biomolecules have been utilized. Biosensors constitute one of the most promising ways to monitor and detect various biomolecules corresponding to diseases. In this study, we demonstrate that the reaction of streptavidin molecules with bioti...

We designed an electrical power loss model to minimize the electrical power losses in large-area monolithic organic photovoltaic (m-OPV) modules. Using the electrical power loss model, we calculated the parasitic electrical power losses on the transparent conductive oxide layer by considering the series resistance and shading losses. We fabricated...

We developed a single-panel LCD microdisplay system using a field-sequential color (FSC) driving method and an organic light-emitting diode (OLED) as a backlight unit (BLU). The 0.76′′ OLED BLU with red, green, and blue (RGB) colors was fabricated by a conventional UV photolithography patterning process and by vacuum deposition of small molecule or...

We report thermally stable diimide nanoclusters that could potentially replace the conventional thick electron transport layer (ETL) in organic light-emitting devices (OLEDs). Bis-[1,10]phenanthrolin-5-yl-bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic diimide (Bphen-BCDI) was synthesized from the corresponding dianhydride and amine moieties, and i...

Hybrid solar cells were fabricated using bulk heterojunction (BHJ) films of poly(3-hexylthiophene) (P3HT) and n-type Si nanowires (n-Si NWs). The n-Si NWs were prepared by the chemical etching of n-Si (100) wafers and then detached physically. The hybrid BHJ films exhibited an extended optical absorption to the near infrared region. Although the ph...

We carried out a study on the change in pore wall thickness depending on the current density in p-type silicon. We attempted the formation of a uniform macropore or nanorod array with a high aspect ratio in p-type silicon by electrochemical etching through the optimization of the hydrogen fluoride (HF)/organic electrolyte composition and the design...

Here we report the effect of introducing nickel oxide (NiO) on the performance of organic light-emitting devices (OLEDs) based on small molecules. For the purpose of aligning the NiO deposition with the conventional OLED process, we employed a thermal evaporation method using the NiO powders. To understand the influence of the NiO introduction, we...

Ordered macropores formed in p-type silicon substrates (10 ~ 20 Ω.cm) by using electrochemical anodization in various HF-containing electrolytes was investigated under different operating conditions. The effect of electrolyte composition and etch pits on controlling the formation of macropores on periodically arranged pores is reported. The results...

Three different cyclic amine dyes, 9-(2-chlorophenyl)-9H-carbazole (CPCz; C18H12ClN), 10-(2-chlorophenyl)-10H-phenoxazine (CPPo; C18H12ClNO), and 10-(2-chlorophenyl)-10H-phenothiazine (CPPt; C18H12ClNS), were synthesized to systematically investigate their optical properties and electronic band structures with molecular microstructure. By the inser...

We report on the effects of surface treatment with N 2 , O 2 , and N 2 O plasmas on the work function of indium–tin oxide (ITO). UV photoelectron spectroscopy (UPS) showed that the work function on the ITO surface treated with N 2 O plasma increased more than that on the samples treated with N 2 or O 2 plasma. X-ray photoelectron spectroscopy (XPS)...

Random and ordered macropore formation in p-type silicon substrate (10 ~ 20 ohm•cm) by electrochemical anodization in various HF-containing electrolytes was investigated under different operating conditions. The effect of electrolyte composition controlling the macropore formation both for random and periodically arranged pores is reported. The rol...

The formation of ordered macropores in a prepatterned p-type silicon wafer by electrochemical anodization in HF:H2O:DMSO (dimethyl sulfoxide) and HF:DMSO solutions was investigated. The pore wall thickness in the solutions was found to be reduced with increasing current density. The pore growth rate was compared using two kinds of etch pit; one is...

A field-sequential color (FSC) LCD micro display using newly designed three primary colors organic light-emitting diode (OLED) device as a backlight unit (BLU) has been developed. The OLED backlight consists of three primary color emitters parallel to each other. The operating frequency is 255Hz. The 0.7″ prototype FSC LCD system using OLED BLU suc...

An active-matrix polymer network liquid crystal display (AMPNLCD) of 1.79″ QCIF(176 × 144) was fabricated. The operating mode of normally black was reversed to normally white by using crossed polarizers. The contrast ratio, as a result, was drastically increased, which was comparable to a conventional liquid crystal display. The response time at a...

Polymer Dispersed Liquid Crystal (PDLC) films, of which the liquid crystal has negative dielectric anisotropy, were prepared from the phase separation between liquid crystal (MJ001317) and the various compositions of resins by common polymerization induced phase separation method. In this work, the effects of resin compositions have been systematic...

Polymer Dispersed Liquid Crystal (PDLC) films, of which the liquid crystal has negative dielectric anisotropy, were prepared from the phase separation between MJ001317 and a variety of compositions of resins by common polymerization induced phase separation method In this work, the effects of resin compositions have been systematically investigated...

Rigid/crosslinked flexible polyimide composites were prepared from soluble polymeric and oligomeric precursors: poly(4,4′-oxydiphenylene pyromellitamic acid) [PMDA-ODA(PAA)], poly(4,4′-oxydiphenylene pyromellitamic diethyl ester) [PMDA-ODA(ES)], acetylene-terminated isoimide oligomer of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride/1,3-bis(3-am...

A soluble poly(amic acid) precursor solution of fully rod-like poly(p-phenylene pyromellitimide) (PMDA-PDA) was spin cast on silicon substrates, followed by soft bake at 80–185°C and subsequent thermal imidization at various conditions over 185–400°C in nitrogen atmosphere to be converted to the polyimide in films. Residual stress generated at the...

Soluble poly(p-phenylene biphenyltetracarboxamic acid) precursor was converted to the polyimide by thermal imidization at various conditions. The structure evolution being occurred during its thermal imidization over 25–400°C was investigated as a function of imidization temperature and time by X-ray scattering with synchrotron radiation sources of...

Several high temperature polyimides, as model polymers with various chain rigidities and chain orders, were synthesized through the polycondensation of p-phenylene diamine (PDA) with five different aromatic dianhydrides [i.e., pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA), benzophen...