Showing papers by "Min Jae Ko published in 2013"
TL;DR: Femtosecond transient study confirms that the improved JSC is due to enhanced electron injection and suppressed charge recombination, and EXAFS reveals that Pb-S bond is reinforced and structural disorder is reduced by interstitially incorporated Hg2+, which is responsible for theEnhanced electron injection, suppressed recombination and stability.
Abstract: The reported photocurrent density (JSC) of PbS quantum dot (QD)-sensitized solar cell was less than 19 mA/cm2 despite the capability to generate 38 mA/cm2, which results from inefficient electron injection and fast charge recombination. Here, we report on a PbS:Hg QD-sensitized solar cell with an unprecedentedly high JSC of 30 mA/cm2. By Hg2+ doping into PbS, JSC is almost doubled with improved stability. Femtosecond transient study confirms that the improved JSC is due to enhanced electron injection and suppressed charge recombination. EXAFS reveals that Pb-S bond is reinforced and structural disorder is reduced by interstitially incorporated Hg2+, which is responsible for the enhanced electron injection, suppressed recombination and stability. Thanks to the extremely high JSC, power conversion efficiency of 5.6% is demonstrated at one sun illumination.
254 citations
TL;DR: A noble water-based thixotropic polymer gel electrolyte containing xanthan gum is reported, which satisfies both the environmentally friendliness and stability against leakage and water intrusion and will provide great insight into the development of efficient and stable water- based electrolytes.
Abstract: For the practical application of dye-sensitized solar cells (DSSCs), it is important to replace the conventional organic solvents based electrolyte with environmentally friendly and stable ones, due to the toxicity and leakage problems. Here we report a noble water-based thixotropic polymer gel electrolyte containing xanthan gum, which satisfies both the environmentally friendliness and stability against leakage and water intrusion. For application in DSSCs, it was possible to infiltrate the prepared electrolyte into the mesoporous TiO2 electrode at the fluidic state, resulting in sufficient penetration. As a result, this electrolyte exhibited similar conversion efficiency (4.78% at 100 mW cm–2) and an enhanced long-term stability compared to a water-based liquid electrolyte. The effects of water on the photovoltaic properties were examined elaborately from the cyclic voltammetry curves and impedance spectra. Despite the positive shift in the conduction band potential of the TiO2 electrode, the open-circu...
90 citations
TL;DR: A new synthetic process of near infrared (NIR)-absorbing copper-indium-selenide (CISe) quantum dots (QDs) and their applications to efficient and completely heavy-metal-free QD-sensitized solar cells (QDSCs).
Abstract: We present a new synthetic process of near infrared (NIR)-absorbing copper–indium–selenide (CISe) quantum dots (QDs) and their applications to efficient and completely heavy-metal-free QD-sensitized solar cells (QDSCs). Lewis acid–base reaction of metal iodides and selenocarbamate enabled us to produce chalcopyrite-structured CISe QDs with controlled sizes and compositions. Furthermore, gram-scale production of CISe QDs was achieved with a high reaction yield of ∼73%, which is important for the commercialization of low-cost photovoltaic (PV) devices. By changing the size and composition, electronic band alignment of CISe QDs could be finely tuned to optimize the energetics of the effective light absorption and injection of electrons into the TiO2 conduction band (CB). These energy-band-engineered QDs were applied to QDSCs, and the quantum-confinement effect on the PV performances was clearly demonstrated. Our best cell yielded a conversion efficiency of 4.30% under AM1.5G one sun illumination, which is comparable to the performance of the best solar cells based on toxic lead chalcogenide or cadmium chalcogenide QDs.
67 citations
TL;DR: The developed method for increasing the reaction rate of dye adsorption is effective for reducing the overall fabrication time without sacrificing the performance and long-term stability of DSSCs.
Abstract: A facile method for increasing the reaction rate of dye adsorption, which is the most time-consuming step in the production of dye-sensitized solar cells (DSSCs), was developed. Treatment of a TiO2 photoanode with aqueous nitric acid solution (pH 1) remarkably reduced the reaction time required to anchor a carboxylate anion of the dye onto the TiO2 nanoparticle surface. After optimization of the reaction conditions, the dye adsorption process became 18 times faster than that of the conventional adsorption method. We studied the influence of the nitric acid treatment on the properties of TiO2 nanostructures, binding modes of the dye, and adsorption kinetics, and found that the reaction rate improved via the synergistic effects of the following: (1) electrostatic attraction between the positively charged TiO2 surface and ruthenium anion increases the collision frequency between the adsorbent and the anchoring group of the dye; (2) the weak anchoring affinity of NO3– in nitric acid with metal oxides enables ...
47 citations
TL;DR: In this article, three new organic sensitizers with phenothiazine chromophores were synthesized and used in dye-sensitized solar cells and the effects of these substituents on the performance of the dyes were investigated by assessing the photophysical, electrochemical, and photovoltaic properties.
44 citations
TL;DR: In this article, the influence of the subsequent sulfurization condition on the morphology, composition and structure of the final Cu2ZnSnS4 (CZTS) thin films was investigated.
41 citations
TL;DR: Improved interparticle connectivity, resulting in faster electron transport, was confirmed by photocurrent transient spectroscopy and electrochemical impedance measurements of the nanoglue-based films.
Abstract: An interparticle binding agent, or nanoglue, was synthesized by a sol–gel process, which facilitated the preparation of well-interconnected TiO2 electrodes at low-temperatures for plastic dye-sensitized solar cells. The viscosity of the nanoglue-based pastes was seven times higher than that obtained in pastes without any nanoglue. The increased viscosity was sufficiently high enough for coating thick films to fabricate TiO2 electrodes. The structural and photovoltaic properties of the films were extensively investigated by varying the amounts of nanoglue. A reduced pore size and greatly enhanced surface area were observed in the nanoglue-based films. Improved interparticle connectivity, resulting in faster electron transport, was confirmed by photocurrent transient spectroscopy and electrochemical impedance measurements of the nanoglue-based films. The electron diffusion length and charge collection efficiency were also enhanced in these nanoglue-based films. A maximum conversion efficiency of 5.43% was achieved in films containing 20 wt% nanoglue fabricated on a plastic substrate under one-sun illumination, even without any additional treatment.
34 citations
TL;DR: In this paper, a low-cost, non-vacuum fabrication route for CuInSe2 and CuInS2 thin films was presented, where binder-free colloidal precursors were prepared using Cu-In intermetallic nanoparticles that were synthesized via a chemical reduction method.
Abstract: A low-cost, nonvacuum fabrication route for CuInSe2 and CuInS2 thin films is presented. To produce these films, binder-free colloidal precursors were prepared using Cu–In intermetallic nanoparticles that were synthesized via a chemical reduction method. The Cu–In alloy precursor films were transformed to CuInSe2 and CuInS2 by reactive annealing in chalcogen-containing atmospheres at atmospheric pressure. The as-synthesized nanoparticles and the annealed films were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry, electron probe X-ray microanalysis, Raman spectroscopy, and Auger electron spectroscopy depth profile measurements to elucidate the phase evolution pathway and the densification mechanism of the Cu–In–Se–S system. Solar cell devices made with CuInSe2 and CuInS2 absorbing layers exhibited power conversion efficiencies of 3.92% and 2.28%, respectively. A comparison of the devices suggested that the microstructur...
31 citations
TL;DR: The results of non-thermal radio-frequency (rf) atmospheric pressure plasma (APP) based deposition of TiO2 nanoparticles on a flexible substrate for the fabrication of dye-sensitized solar cells (DSSCs) show that superior film properties can be obtained when compared with the thermal sintering process operating at 450 °C.
Abstract: A key challenge to the industrial application of nanotechnology is the development of fabrication processes for functional devices based on nanomaterials which can be scaled up for mass production. In this report, we disclose the results of non-thermal radio-frequency (rf) atmospheric pressure plasma (APP) based deposition of TiO2 nanoparticles on a flexible substrate for the fabrication of dye-sensitized solar cells (DSSCs). Operating at 190 C without a vacuum enclosure, the APP method can avoid thermal damage and vacuum compatibility restrictions and utilize roll-to-roll processing over a large area. The various analyses of the TiO2 films demonstrate that superior film properties can be obtained by the nonthermal APP method when compared with the thermal sintering process operating at 450 C. The crystallinity of the anatase TiO2 nanoparticles is significantly improved without thermal agglomeration, while the surface defects such as Ti 3+ ions are eliminated, thus providing efficient charge collecting properties for solar cells. Finally, we successfully fabricated a flexible DSSC with an energy conversion efficiency of 4.2% using a transparent plastic substrate. This work demonstrates the potential of nonthermal APP technology in the area of device-level, nano-enabled material manufacturing.
27 citations
TL;DR: In this paper, a thin poly(ethyleneoxide) (PEO) layer is formed on the quantum dot (QDs) film using coordination bonding between the ether group in the PEO and Cd metal ions in the QDs, acting as passivation layer to suppress substitution reaction and anodic oxidation.
26 citations
TL;DR: In this article, the authors report the synthesis, characterization, and solar cell properties of new donor-acceptor-type low band gap polymers (POBDTPD and PEBDTPD) that incorporate dialkoxybenzodithiophene (BDT) as the donor and N-octyl-2,7-dithia-5-azacyclopenta[a]pentalene-4,6-dione (DTPD), as the acceptor.
Abstract: We report the synthesis, characterization, and solar cell properties of new donor–acceptor-type low band gap polymers (POBDTPD and PEBDTPD) that incorporate dialkoxybenzodithiophene (BDT) as the donor and N-octyl-2,7-dithia-5-azacyclopenta[a]pentalene-4,6-dione (DTPD) as the acceptor. The newly developed DTPD moiety was carefully designed to lower a band gap via strong interaction between donor–acceptor moieties and keep polymer energy levels deep. Remarkably, the DTPD acceptor moiety effectively widens the light absorption range of the polymers up to ∼900 nm while positioning their HOMO and LUMO levels in the optimal range, i.e., −5.3 and −4.0 eV, respectively, for high power conversion efficiencies (PCEs) as we intended. Solar cell devices were fabricated according to the structure ITO/PEDOT:PSS/photoactive (polymer:PC70BM)/TiO2/Al. The POBDTPD devices exhibited a PCE of 4.7% with a Voc of 0.70 V, a Jsc of 10.6 mA/cm2, and a FF of 0.64. The PEBDTPD devices yielded a higher PCE of 5.3% with a Voc of 0.72...
TL;DR: In this paper, a simple formula is presented based on Faraday's law to quantitatively estimate the density of the electrodeposited thin films; from this, it was found that the as-deposed films had a very high relative density of 0.73.
TL;DR: In this article, the authors characterized the electrical properties of ambipolar polymer field effect transistors (PFETs) based on the lowband-gap polymer, pNAPDO-DPP-EH.
Abstract: We characterized the electrical properties of ambipolar polymer field-effect transistors (PFETs) based on the low-band-gap polymer, pNAPDO-DPP-EH. The polymer consisted of electron-rich 2,6-di(thienyl)naphthalene units with decyloxy chains (NAPDO) and electron-deficient diketopyrrolopyrrole units with 2-ethylhexyl chains (DPP-EH). The as-spun pNAPDO-DPP-EH PFET device exhibited ambipolar transport properties with a hole mobility of 3.64 × 10–3 cm2/(V s) and an electron mobility of 0.37 × 10–3 cm2/(V s). Thermal annealing of the polymer film resulted in a dramatic increase in the carrier mobility. Annealing at 200 °C yielded hole and electron mobilities of 0.078 and 0.002 cm2/(V s), respectively. The mechanism by which the mobility had improved was investigated via grazing incidence X-ray diffraction studies, atomic force microscopy, and temperature-dependent transport measurements. These results indicated that thermal annealing improved the polymer film crystallinity and promoted the formation of a longer...
TL;DR: With M-DSSCs based on a PEDOT/polymer spacer layer, a power conversion efficiency of 7.73% was achieved, which is, to the best of the knowledge, the highest efficiency for M- DSSCs to date.
Abstract: Monolithic dye-sensitized solar cells (M-DSSCs) provide an effective way to reduce the fabrication cost of general DSSCs since they do not require transparent conducting oxide substrates for the counter electrode. However, conventional monolithic devices have low efficiency because of the impediments resulting from counter electrode materials and spacer layers. Here, we demonstrate highly efficient M-DSSCs featuring a highly conductive polymer combined with macroporous polymer spacer layers. With M-DSSCs based on a PEDOT/polymer spacer layer, a power conversion efficiency of 7.73% was achieved, which is, to the best of our knowledge, the highest efficiency for M-DSSCs to date. Further, PEDOT/polymer spacer layers were applied to flexible DSSCs and their cell performance was investigated.
TL;DR: In this paper, two metal-free organic dyes bridged by anthracene-mediated π-conjugated moieties were successfully synthesized for use in a dye-sensitized solar cell (DSSC).
Abstract: Two new metal-free organic dyes bridged by anthracene-mediated π-conjugated moieties were successfully synthesized for use in a dye-sensitized solar cell (DSSC). A N,N-diphenylthiophen-2-amine unit in these dyes acts as an electron donor, while a (E)-2-cyano-3-(thiophen-2-yl)acrylic acid group acts as an electron acceptor and an anchoring group to the TiO2 electrode. The photovoltaic properties of (E)-2-cyano-3-(5-((10-(5(diphenylamino)thiophen-2-yl)anthracen-9-yl)ethynyl)thiophen-2-yl)acrylic acid (DPATAT) and (E)-2cyano-3-(5'-((10-(5-(diphenylamino)thiophen-2-yl)anthracen-9-yl)ethynyl)-2,2'-bithiophen-5-yl)acrylic acid (DPATABT) were investigated to identify the effect of conjugation length between electron donor and acceptor on the DSSC performance. By introducing an anthracene moiety into the dye structure, together with a triple bond and thiophene moieties for fine-tuning of molecular configurations and for broadening the absorption spectra, the short-circuit photocurrent densities (Jsc), and open-circuit photovoltages (Voc) of DSSCs were improved. The improvement of Jsc in DSSC made of DPATABT might be attributed to much broader absorption spectrum and higher molecular extinction coefficient (e) in the visible wavelength range. The DPATABT-based DSSC showed the highest power conversion efficiency (PCE) of 3.34% (ηmax = 3.70%) under AM 1.5 illumination (100 mW cm �2 ) in a photoactive area of 0.41 cm 2 , with the Jsc of 7.89 mA cm �2 , the Voc of 0.59 V, and the fill factor (FF) of 72%. In brief, the solar cell performance with DPATABT was found to be better than that of DPATAT-based DSSC.
TL;DR: In this paper, iridium (Ir)-coated counter electrodes (CEs) were used for dye-sensitized solar cells (DSSCs) in order to replace the traditional Pt-based counter electrodes in DSSCs.
TL;DR: Three-dimensional nanostructures of TiO2 related materials including nanotubes, electron acceptor materials in hybrid polymer solar cells, and working electrodes of dye sensitized solar cells (DSSCs) were visualized by electron tomography as well as TEM micrographs.
TL;DR: In this article, a reversed hybrid tandem photovoltaic (H-Si:H) was constructed with high bandgap hydrogenated amorphous silicon (a-SiH) with plasma-enhanced chemical vapor deposition onto a solution-processed low bandgap OPV subcell.
Patent•
11 Jan 2013TL;DR: In this paper, a polymer gel electrolyte composition is proposed to solve the problem of leakage and volatilization of a dye-sensitized solar cell, which is free from problems of leakage, and can be used for a long period of time.
Abstract: Disclosed is a polymer gel electrolyte composition. The composition includes an aqueous solution of a polysaccharide-based polymer and a liquid electrolyte in which a redox derivative is mixed with an organic solvent. The composition is easy to inject. The composition is free from problems of leakage and volatilization, thus being environmentally friendly. Further disclosed is a highly efficient dye-sensitized solar cell using the composition. The dye-sensitized solar cell is stable for a long period of time and can be readily commercialized.
Patent•
26 Aug 2013TL;DR: In this paper, a thin-film solar cell with an ionic liquid as an absorber layer is presented. But the method uses a non-vacuum electrodeposition process that is appropriate for large-area mass production and is thus cost effective compared to a vacuum process.
Abstract: A Cu2ZnSnS4-xSex (0≦x≦4) thin film solar cell is disclosed. The thin film solar cell includes a Cu2ZnSnS4-xSex (0≦x≦4) thin film as an absorber layer produced by forming a precursor film composed of Cu, Zn, Sn, and Se using an ionic liquid as a solvent through a constant current process and annealing the precursor film with sulfur. Also disclosed is a method for fabricating the thin film solar cell. The method uses a non-vacuum electrodeposition process that is appropriate for large-area mass production and is thus cost effective compared to a vacuum process. In addition, since the method uses an ionic liquid, the formation of by-products harmful to humans as a result of side reactions is suppressed. Furthermore, the method uses a one-step electrodeposition process, which enables the deposition of a maximum of four elements at one time, or a multi-step deposition process, and an annealing process.
TL;DR: In this article, a low band gap donor-acceptor copolymer (PDTDPP-Oct) was designed and synthesized, which is composed of alternating dithieno[3,2- b :2′,3′- d ]thiophene and bis-thienyl-diketopyrrolo[ 3,4- c ]pyrrole units.
TL;DR: In this article, the authors investigated the effects of vacuum annealing on the surface electronic structure and the work function of single-walled carbon nanotubes (SWCNTs).
Abstract: We investigated the effects of vacuum annealing on the surface electronic structure and the work function of single-walled carbon nanotubes (SWCNTs). We changed the doping type of semiconducting single-walled carbon nanotubes (semi-SWCNTs) from p-type to n-type, and investigated their optical properties. The HNO3 treated p-type SWCNT network was converted to n-type after vacuum annealing due to formation of C-N bond. The C 1s sp2 binding energy of the vacuum annealed semi-SWCNTs was shifted toward a higher binding energy about 0.42 eV, which indicates a raising Fermi level as much as 0.42 eV compared with the intrinsic semi-SWCNTs. In addition, the work function of the vacuum annealed semi-SWCNT was observed towards lower energies. It is considered that the C-N bonding of semi-SWCNTs creates a donor level near the bottom of the conduction band, thus raising the Fermi level. The ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy revealed that the increased binding energy of C 1s sp...
01 Apr 2013
Patent•
15 Mar 2013TL;DR: In this article, a method for producing polythiophene star copolymer capable of being self-doped by an external stimulus, which includes the steps of: forming a polyphotonic macroinitiator made by introducing a living radical polymerizable functional group into an end of polyphysiope or a derivative thereof, forming through living radical polymeric polymerization a polymer macro-initiators for providing at least a dopant selected from the group consisting of sulfonic acid radical, carboxylic acid radical and phosphoric acid radical; and polymerizing
Abstract: The present invention provides a method for producing polythiophene star copolymer capable of being self-doped by an external stimulus, which includes the steps of: forming a polythiophene macroinitiator made by introducing a living radical polymerizable functional group into an end of polythiophene or a derivative thereof; forming through living radical polymerization a polymer macroinitiator for providing by an external stimulus at least a dopant selected from the group consisting of sulfonic acid radical, carboxylic acid radical and phosphoric acid radical; and polymerizing the polythiophene macroinitiator added with the polymer macroinitiator and at least one kind of divinyl monomer to produce the polythiophene star copolymer. The polythiophene star copolymer capable of being self-doped by an external stimulus according to the present invention is a self-doped material to stably increase conductivity, and can be used as a material for a conductive film.
Patent•
22 Oct 2013TL;DR: In this article, an environment-friendly polymer gel electrolyte composition facilitates the injection of electrolyte, reduces leakage and volatilization, thereby providing a dye-sensitized solar cell with excellent long term stability and high efficiency.
Abstract: PURPOSE: An environment-friendly polymer gel electrolyte composition facilitates the injection of electrolyte, reduces leakage and volatilization, thereby providing a dye-sensitized solar cell with excellent long term stability and high efficiency. CONSTITUTION: A polymer gel electrolyte composition for a dye-sensitized solar cell comprises a polysaccharide-based polymer aqueous solution and a liquid electrolyte mixed of an oxidation-reduction derivative and an organic solvent. A manufacturing method of a polymer gel electrolyte composition comprises a step of manufacturing a polymer gel aqueous solution by dispersing polysaccharide-based polymer into a solvent; a step of manufacturing a liquid electrolyte by mixing an oxidation-reduction derivative and an organic solvent; and a step of mixing the polysaccharide-based polymer gel aqueous solution and liquid electrolyte.
Patent•
25 Oct 2013TL;DR: In this article, a polythiophene star polymer copolymer capable of self doping by external stimulus is provided to steadily increase conductivity as a self-doping material, thereby being used for the material of a conductive thin film.
Abstract: PURPOSE: A polythiophene star polymer copolymer capable of self doping by external stimulus is provided to steadily increase conductivity as a self-doping material, thereby being used for the material of a conductive thin film CONSTITUTION: A manufacturing method of a polythiophene star polymer copolymer capable of self doping by external stimulus comprises: a step of forming a polythiophene macro initiator, a functional group capable of the polymerization of living radical is introduced at the terminus of polythiophene or the derivative; a step of forming a polymer macro initiator providing one or more dopants selected from sulfone group, carboxyl group, and phosphate group by external stimulus through living radical polymerization; and a step of polymerizing the polythiophene star polymer copolymer by adding the polymer macro initiator and at least one kind of divinyl monomer to the polythiophene macro initiator
Patent•
01 Aug 2013TL;DR: In this paper, a method for producing a synthesis gas using a solid acid capable of remarkably decreasing production of environmental pollutants such as carbon dioxide is described. But this method is not suitable for the synthesis of hydrogen.
Abstract: The present disclosure relates to a method for producing a synthesis gas using a solid acid, more particularly to a method for producing a synthesis gas using a solid acid capable of remarkably decreasing production of environmental pollutants such as carbon dioxide, which includes producing hydrogen by reacting a solid acid with water and producing a synthesis gas by reacting the produced hydrogen with a carbon compound.