• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.88.2-88.2
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• 2010

Dye-sensitized solar cells (DSSCs) have attracted considerable attention on account of their high solar energy-to-conversion efficiencies and low cost processes compared to conventional p-n junction solar cells. The mechanism of DSSC is based on the injection of electrons from the photo excited dyes into the conduction band of the semiconductor electrode. The oxidized dye is reduced by the hole injection into either the hole conductor or the electrolyte. Thus, the light harvesting effect of dye plays an important role in capturing the photons and generating the electron/hole pair, as well as transferring them to the interface of the semiconductor and the electrolyte, respectively. We used the organic fluorescence materials which can absorb short wavelength light and emit longer wavelength region where dye sensitize effectively. In this work, the DSSCs were fabricated with fluorescence materials added $TiO_2$ photo-electrode which were sensitized with metal-free organic dyes. The photovoltaic performances of fluorescence aided DSSCs were compared, and the recombination dark current curves and the incident photon-to-current (IPCE) efficiencies were measured in order to characterize the effects of the additional light harvesting effect in DSSC. Electro-optical measurements were also used to optimize the fluorescence material contents on TiO2 photo-electrode surface for higher conversion efficiency (${\eta}$), fill factor (FF), open-circuit voltage (VOC) and short-circuit current (ISC). The enhanced light harvesting effect by the judicious choice/design of the fluorescence materials and sensitizing dyes permits the enhancement of photovoltaic performance of DSSC.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.225-225
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• 2013

Nanostructured noble metals have been attractive for their unusual optical properties and are widely utilized for various purposes. The optical properties mainly originating from collective electron oscillation can assist direct energy conversion via surface plasmon resonances. Here, we investigated the effect of surface plasmons of silver nanowires on the generation of hot electrons. It is reported that the surface plasmons of silver nanowires exhibit longitudinal and transverse modes, depending on the aspect ratio of the nanowires. In order to measure the hot electron flow through the metallic nanowires, chemically modified Au/TiO2 Schottky diodes were employed as the electric contact. The silver nanowires were deposited on a Au metal layer via the spray method to control uniformity and the amount of silver nanowire deposited. We measured the hot electron flow generated by photon absorption on the silver nanowires deposited on the Au/TiO2 Schottky diodes. The incident photon-to-current efficiency was measured a function of the photon energy, revealing two polarization modes of siliver nanowires: transverse and longitudinal modes. UV-Vis spectra exhibited two polarization modes, which are also consistent with the photocurrent measurements. Good correlation between the IPCE and UV-vis measurements suggests that hot electron measurement on nanowires on nanodiodes is a useful way to reveal the intrinsic properties of surface plasmons of nanowires.

• Transactions on Electrical and Electronic Materials
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• v.5 no.3
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• pp.89-92
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• 2004

For improving solar efficiencies, down conversion of high-energy photons to visible lights is discussed. The losses due to thermalization of charge carriers generated by the absorption of high-energy photons, can largely be reduced in a solar cell if more than one electron-hole pair can be generated per incident photon. The solar cell was constructed of dye-sensitized anatase-based TiO$_2$, approximately 30nm particle size, 6$\mu\textrm{m}$thickness, and 6${\times}$6$\textrm{mm}^2$ active area, Pt counter electrode and I$_3$$\^$-/I$_2$$\^$-/ electrolyte. After correction for losses due to light reflection and absorption by the conducting glass, the conversion of photons to electric current is practically quantitative in the plateau region of the curves. The incident photon to current conversion efficiency(IPCE) of N3 used as a dye in this work is about 80% at around 590nm and 610nm which is the emission spectrum of Eu doped LGF. The Eu doped LGF powder was prepared by conventional ceramic process, and used as a down converter for DSC after spin coated on the slide glass and fired.

• Bulletin of the Korean Chemical Society
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• v.32 no.8
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• pp.2671-2676
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• 2011

Nanocrystalline $TiO_2$ spherical particle (NP) with a dimension of 5 ${\times}$ 5.5 nm and several nanorods (NR) with different aspect ratios (diameter ${\times}$ length: 5 ${\times}$ 8.5, 4 ${\times}$ 15, 4 ${\times}$ 18 and 3.5 ${\times}$ 22 nm) were selectively synthesized by a solvothermal process combined with non-hydrolytic sol-gel reaction. With varying the molar ratio of TTIP to oleic acid from 1:1 to 1:16, the NRs in the pure anatase phase were elongated to the c-axis direction. The prepared NP and NRs were applied for the formation of nanoporous $TiO_2$ layers in dye-sensitized solar cell (DSSC). Among them, NR2 ($TiO_2$ nanorod with 4 ${\times}$ 15 nm) exhibited the highest cell performance: Its photovoltaic conversion efficiency (${\eta}$) of 6.07%, with $J_{sc}$ of 13.473 mA/$cm^2$, $V_{oc}$ of 0.640 V, and FF of 70.32%, was 1.44 times that of NP with a size of 5 ${\times}$ 5.5 nm. It was observed from the transient photoelectron spectroscopy and the incident photon to current conversion efficiency (IPCE) spectra that the $TiO_2$ films derived from NR2 demonstrate the longest electron diffusion length ($L_e$) and the highest external quantum efficiency (EQE).

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.305-305
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• 2010

It is known that a pulse of electrons of high kinetic energy (1-3 eV) in metals can be generated with the deposition of external energy to the surface such as in the absorption of light or in exothermic chemical processes. These energetic electrons are not in thermal equilibrium with the metal atoms and are called "hot electrons" The concept of photon energy conversion to hot electron flow was suggested by Eric McFarland and Tang who directly measured the photocurrent on gold thin film of metal-semiconductor ($TiO_2$) Schottky diodes [1]. In order to utilize this scheme, we have fabricated metal-semiconductor Schottky diodes that are made of Pt or Au as a metallic layer, Si or $TiO_2$ as a semiconducting substrate. The Pt/$TiO_2$ and Pt/Si Schottky diodes are made by PECVD (Plasma Enhanced Chemical Vapor Deposition) for $SiO_2$, magnetron sputtering process for $TiO_2$, e-beam evaporation for metallic layers. Metal shadow mask is made for device alignment in device fabrication process. We measured photocurrent on Pt/n-Si diodes under AM1.5G. The incident photon to current conversion efficiency (IPCE) at different wavelengths was measured on the diodes. We also show that the steady-state flow of hot electrons generated from photon absorption can be directly probed with $Pt/TiO_2$ Schottky diodes [2]. We will discuss possible approaches to improve the efficiency of photon energy conversion.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.76-76
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• 2011

Polymer-fullerene based bulk heterojunction (BHJ) solar cells can be fabricated in large area using low-cost roll-to-roll manufacturing methods. However, because of the low mobility of the BHJ materials, there is competition between the sweep-out of the photogenerated carriers by the built-in potential and recombination within the thin BHJ film [12-15]. Useful film thicknesses are limited by recombination. Thus, there is a need to increase the absorption by the BHJ film without increasing film thickness. Metal nanoparticles exhibit localized surface plasmon resonances (LSPR) which couple strongly to the incident light. In addition, relatively large metallic nanoparticles can reflect and scatter the light and thereby increase the optical path length within the BHJ film. Thus, the addition of metal nanoparticles into BHJ films offers the possibility of enhanced absorption and correspondingly enhanced photo-generation of mobile carriers. In this work, we have demonstrated several positive effects of shape controlled Au and Ag nanoparticles in organic P3HT/PC70BM, PCDTBT/PC70BM, Si-PCPDTBT/PC70BM BHJ-based PV devices. The use of an optimized concentration of Au and Ag nanomaterials in the BHJ film increases Jsc, FF, and the IPCE. These improvements result from a combination of enhanced light absorption caused by the light scattering of the nanomaterials in an active layer. Some of the metals induce the plasmon light concentration at specific wavelength. Moreover, improved charge transport results in low series resistance.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2009.06a
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• pp.467-470
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• 2009

A novel 8 V DC power source with an external series-parallel connection of 50 Dye-Sensitized Solar Cells(DSSCs) has been proposed. One DSC has the optimized length to width ratio of $5.2{\times}2.6$ cm and an active area 8 $cm^2$($4.62{\times}1.73$ cm) which attained a conversion efficiency of 4.2%. From the electrochemical impedance spectroscopic analysis, it was found that the resistance elements related to the Pt electrode and electrolyte interface behave like that of diode and the series resistance corresponds to the sum of the other resistance elements. In addition, the TEMoo mode pulsed Nd:YAG laser beam is used to improve the incident photon to current efficiency(IPCE) of DSSC. From this result, this novel 8V-0.38A DC power source shows stable performance with an energy conversion efficiency of about 4.5% under 1 sun illumination(AM 1.5, Pin of 100 $mW/cm^2$).

• Korean Journal of Materials Research
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• v.31 no.11
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• pp.619-625
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• 2021

Cu₂ZnSn(S,Se)₄ (CZTSSe) based thin-film solar cells have attracted growing attention because of their earth-abundant and non-toxic elements. However, because of their large open-circuit voltage (V_oc)-deficit, CZTSSe solar cells exhibit poor device performance compared to well-established Cu(In,Ga)(S,Se)₂ (CIGS) and CdTe based solar cells. One of the main causes of this large V_oc-deficit is poor absorber properties for example, high band tailing properties, defects, secondary phases, carrier recombination, etc. In particular, the fabrication of absorbers using physical methods results in poor surface morphology, such as pin-holes and voids. To overcome this problem and form large and homogeneous CZTSSe grains, CZTSSe based absorber layers are prepared by a sputtering technique with different RTA conditions. The temperature is varied from 510 ℃ to 540 ℃ during the rapid thermal annealing (RTA) process. Further, CZTSSe thin films are examined with X-ray diffraction, X-ray fluorescence, Raman spectroscopy, IPCE, Energy dispersive spectroscopy and Scanning electron microscopy techniques. The present work shows that Cu-based secondary phase formation can be suppressed in the CZTSSe absorber layer at an optimum RTA condition.

• Journal of the Korean institute of surface engineering
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• v.56 no.2
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• pp.137-146
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• 2023

Nanosized TiO₂ has been widely investigated in photoelectrochemical or photocatalytic applications due to their intrinsic properties such as suitable band position, high photocorrosion resistance, and surface area. In this study, to achieve the high efficiency in photoelectrochemical and photocatalytic performance, TiO₂ nanotubular structures were formed by anodization at various temperatures and times. The morphological and crystal structure of the anodized TiO₂ nanotubes (NTs) were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). The photoelectrochemical (PEC) properties and incident photon-to-current conversion efficiency (IPCE) of the TiO₂ NTs were studied with different lengths and morphologies. From the detailed investigations, the optimum thickness of TiO₂ nanotubes was 3 ㎛. Moreover, we found that the optimum photocatalytic pollutant removal efficiency of TiO₂ nanotubes for photodegradation of Rhodamine B (RhB) under simulated solar light was 5.34 ㎛ of tube length.

• 한국신재생에너지학회:학술대회논문집
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• 2010.06a
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• pp.89.1-89.1
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• 2010

Since Gratzel and co-workers developed a new type of solar cell based on the nanocrystalline $TiO_2$ electrode, dye-sensitized solar cells (DSSCs) have attracted considerable attention on account of their high solar energy-to-conversion efficiencies (11%), their easy manufacturing process with low cost production compared to conventional p-n junction solar cells. The mechanism of DSSC is based on the injection of electrons from the photoexcited dye into the conduction band of nanocrystalline $TiO_2$. The oxidized dye is reduced by the hole injection process from either the hole counter or electrolyte. Thus, the electronic structures, such as HOMO, LUMO, and HOMO-LUMO gap, of dye molecule in DSSC are deeply related to the electron transfer by photoexcitation and redox potential. To date, high performance and good stability of DSSC based on Ru-dyes as a photosensitizer had been widely addressed in the literatures. DSSC with Ru-bipyridyl complexes (N3 and N719), and the black ruthenium dye have achieved power conversion efficiencies up to 11.2% and 10.4%, respectively. However, the Ru-dyes are facing the problem of manufacturing costs and environmental issues. In order to obtain even cheaper photosensitizers for DSSC, metal-free organic photosensitizers are strongly desired. Metal-free organic dyes offer superior molar extinction coefficients, low cost, and a diversity of molecular structures, compared to conventional Ru-dyes. Recently, novel photosensitizers such as coumarin, merocyanine, cyanine, indoline, hemicyanine, triphenylamine, dialkylaniline, bis(dimethylfluorenyl)-aminophenyl, phenothiazine, tetrahydroquinoline, and carbazole based dyes have achieved solar-to-electrical power conversion efficiencies up to 5-9%. On the other hand, organic dye molecules have large ${\pi}$-conjugated planner structures which would bring out strong molecular stacking in their solid-state and poor solubility in their media. It was well known that the molecular stacking of organic dyes could reduce the electron transfer pathway in opto-electronic devices, significantly. In this paper, we have studied on synthesis and characterization of dendritic organic dyes with different number of electron acceptor/anchoring moieties in the end of dendrimer. The photovoltaic performances and the incident photon-to-current (IPCE) of these dyes were measured to evaluate the effects of the dendritic strucuture on the open-circuit voltage and the short-circuit current.