Yunyoung Noh

Effect of the thickness of the Ru-coating on a counter electrode on the performance of a dye-sensitized solar cell

A ruthenium (Ru) catalytic layer was assessed as the counter electrode (CE) in dye sensitized solar cells (DSSCs) by examining the effect of the Ru thickness on the DSSC performance. Ru films with different thicknesses (34, 46, 69 and 90 nm) were deposited on glass/fluorine-doped tin oxide (FTO) substrates as the CE by atomic layer deposition (ALD) at 250 °C using RuDi as the precursor and O2 as the reaction gas. Finally, a 0.45 cm2 DSSC of glass/FTO/TiO2/dye(N719)/electrolyte(C6DMII, GSCN)/Ru CE structure was prepared. The properties of the DSSCs were examined by field emission scanning electron microscopy (FESEM), four-point-probe, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), current-voltage (I–V), incident photon-to-current conversion efficiency (IPCE), and dark current measurements. FESEM showed that the crystallized Ru films had been deposited quite uniformly and conformally on the glass/FTO surface. The sheet resistance of the Ru film decreased with increasing Ru thickness. CV profiling revealed an increase in catalytic activity with increasing film thickness. The charge transfer resistance at the interface between the Ru-coated CE and electrolyte decreased with increasing Ru thickness. I–V profiling showed that the energy conversion efficiency was increased up to 3.40 % by increasing the Ru thickness. Moreover, the IPCE and dark current results showed the efficiency of the Ru-coated CE was comparable to that of a conventional platinum (Pt) CE.

Properties of an Au/Pt bilayered counter electrode in dye sensitized solar cells

A Ru/Ti bilayer to a flat glass substrate was applied as a counter electrode to improve the energy conversion efficiency of a dye-sensitized solar cell device with the structure of glass/FTO/blocking layer/TiO2/N719(dye)/electrolyte/(50 nm Ru-50 nm Ti)/glass. For comparison, a 100 nm-thick Ru counter electrode on a flat glass substrate was also prepared using the same method. The photovoltaic properties, such as the short circuit current density, open circuit voltage, fill factor, energy conversion efficiency and impedance, were characterized using a solar simulator and potentiostat. The phase of the bilayered films was examined by x-ray diffraction. The measured energy conversion efficiency of the dye-sensitized solar cell device with a Ru/Ti bilayer counter electrode was 2.40%. The efficiency was 1.48 times larger that of the dye-sensitized solar cell with the 100 nm Ru counter electrode. The new phase of RuTi led to a decrease in resistivity and an increase in catalytic activity. The interface resistance at the interface between the counter electrode and electrolyte decreased when Ru/Ti bilayer thin films were applied. This suggests that Ru/Ti bilayer thin films improve the efficiency of dye-sensitized solar cells.

Formation of ruthenium-dots on counter electrodes for dye sensitized solar cells

A 34 nm-thick ruthenium layer was deposited on a flat glass substrate by atomic layer deposition at low temperatures followed by the formation of self-aligned Ru micro or nano-dots by rapid thermal annealing for 30 seconds at 400°C. The resulting substrates were re-coated with another 34 or 69 nm-thick Ru layers by ALD at 250°C. Finally, the effective area of 0.45 cm2 dye sensitized solar cell with a glass / FTO / TiO2 / dye / electrode / (nano-dots Ru / Ru)/glass structure was fabricated. The microstructure was examined by field emission scanning electron microscopy and atomic force microscopy. The photovoltaic properties, such as the short circuit current density, open circuit voltage, fill factor, and energy conversion efficiency, were characterized using a solar simulator and potentiostat. FE-SEM confirmed that the 34 nm and 69 nm-thick Ru layers re-deposited by the second ALD process showed a 65% and 49% larger surface area, respectively, than the flat glass substrate due to the rearranged nano-dots. The ECE of the final DSSC was 2.62%, which was a 1.45 times larger than that of the 34 nm-Ru flat glass substrate. These results suggest that the efficiency of DSSCs can be improved by increasing the effective surface area of a counter electrode by low temperature ALD.

Properties of the Cu/Pt Bilayered Counter Electrode Employed Dye Sensitized Solar Cells

In order to improve energy-conversion efficiency using a Cu/Pt bilayer on a flat-glass substrate of a counter electrode (CE), a 0.45 cm dye-sensitized solar-cell (DSSC) device (with glass/FTO/blocking layer/ TiO2/N719 (dye)/electrolyte/50 nm-Pt/50 nm-Cu/glass) was prepared. For comparison, 100-nm thick Cu and Pt CEs were also prepared on flat-glass substrates using the same method. The photovoltaic properties of the DSSC device, such as short-circuit current-density (Jsc), open-circuit voltage (Voc), fill factor (FF), energy-conversion efficiency (ECE), and impedance, were checked using a solar simulator and potentiostat. The sheet resistance was examined using a four point probe. The phases of the bi-layered films were examined using X-ray diffraction. The measured energy-conversion efficiency of the DSSC devices with only Pt and Cu/Pt bilayer counter electrodes was 4.60% and 5.72%, respectively. The sheet resistance and interface (CE/electrolyte) resistance of a Cu/Pt bilayer were smaller than those of a Pt-only layer. The phases of the Cu/Pt bi-layered films were identified in pure Cu and Pt without any intermetallic layer. We concluded that the increase in the efficiency of DSSCs employing Cu/Pt, resulted from employing the low-resistive Cu layer. †(Received August 20, 2013)

Properties of the nano-thick Pt/W bilayered catalytic layer employed dye sensitized solar cells

A Pt/W bilayered catalytic layer on a flat glass substrate was used as a counter electrode to improve the energy conversion efficiency of a dye-sensitized solar cell device with the structure of 0.45 cm2 effective area of glass/FTO/blocking layer/TiO2/N719 (dye)/electrolyte/50 nm Pt/50 nm W/glass. For comparison, 100 nm-thick Pt and W counter electrodes on flat glass substrates were also prepared using the same procedure. The photovoltaic properties, such as the short circuit current density, open circuit voltage, fill factor, energy conversion efficiency and impedance were characterized using a solar simulator and potentiostat. The phases and microstructures of the catalytic layers were examined by x-ray diffraction and field emission electron microscopy. The measured energy conversion efficiencies of the dye-sensitized solar cell devices with Pt only and Pt/W bilayer counter electrodes were 4.60% and 6.54%, respectively. The interface resistance at the interface between the counter electrode and electrolyte decreased when a Pt/W bilayered thin film was applied. The increase in efficiency resulted from the effect of compressive strain field formed by the intermetallic layer of Pt2W at Pt and W layer interface. This suggests that the use of Pt/W bilayered catalytic layers improves the efficiency of the dye-sensitized solar cells compared to those using the conventional Pt layers.

Properties of a Dye Sensitized Solar Cell using Electrodes with Au Nano Powder Blocking Layers

Jeongho Song, Yunyoung Noh, Minkyoung Choi, Kwangbae Kim, and Ohsung Song* Department of Materials Science and Engineering, University of Seoul, Seoul 02504, Republic of Korea Abstract: We prepared working electrodes with blocking layers containing 0.0∼0.5 wt% Au nano powder to improve the energy conversion efficiencies (ECEs) of a dye sensitized solar cell (DSSC). TEM, FE-SEM, and AFM were used to characterize microstructure. XRD and micro-Raman were used to determine the phase and localized surface plasmon resonance (LSPR) effect of the blocking layer with Au nano powder. A solar simulator and a potentiostat were used to confirm the photovoltaic properties of the DSSC with the Au nano powder. From the results of the microstructure analysis, we confirmed that the Au nano powder had particle sizes of less than 70 nm, dispersed uniformly on the blocking layer. Based on the phase and composition analysis, we identified the presence of Au, and the Raman intensity increased as the amount of Au was increased. The photovoltaic results showed that the ECE reached 5.52% with the Au addition, compared to an ECE of 5.00% without the Au addition. This enhancement was due to the increased LSPR of the blocking layer with the Au addition. Our results suggest that we might improve the efficiency of a DSSC by the proper addition of Au nano powder on the blocking layer. †(Received November 24, 2015; Accepted February 22, 2016)

Degradation of the Pd catalytic layer electrolyte in dye sensitized solar cells

Abstract A TCO-less palladium (Pd) catalytic layer on the glass substrate was assessed as the counter electrode(CE) in a dye sensitized solar cell (DSSC) to confirm the stability of Pd with the I - /I 3- electrolyte on the DSSC performance. A 90nm-thick Pd film was deposited by a thermal evaporator. Finally, DSSC devices of 0.45cm 2 with glass/FTO/blocking layer/TiO 2 /dye/electrolyte(10 mM LiI + 1 mM I 2 + 0.1 M LiClO 4 in acetonitrile solution)/Pd/glassstructure was prepared. We investigated the microstructure and photovoltaic property at 1 and 12 hours after the sample preparation. The optical microscopy, field emission scanning electron microscopy (FESEM), cyclic voltammetry measurement (C-V), and current voltage (I-V) were employed to measure the microstructure and photovoltaic property evolution. Microstructure analysis showed that the corrosion by reaction between the Pd layer and the electrolyte occurred as time went by, which led the decrease of the catalytic activity and the efficiency. I-Vresult revealed that the energy conversion efficiency after 1 and 12 hours was 0.34% and 0.15%, respectively. Our results implied that we might employ the other non- I

MWCNT employed counter electrode for DSSCs

In this study, we proposed and investigated the performance of DSSCs with the multi-walled carbon nanotube (MWCNT) on the counter electrode(CE). The 0.45cm2 DSSC device of glass/FTO/TiO2 blocking layer/TiO2(8.5um)/Dye(N719)/ electrolyte (C6DMII,GSCN)/MWCNT/FTO/glass was fabricated, and then the surface morphology of CEs and the energy conversion efficiency of the DSSC device were characterized by scanning electron microscope(SEM), photocurrent-voltage(I–V), cyclic voltammetry(C-V), and Impedance measurement. We confirmed that the efficiency of the DSSC increased from 1.92% to 3.25% as the amount of MWCNT increased from 0.01g to 0.06g. In addition, we expected that the catalytic activity and CE resistance of the MWCNT employed CE would show the similar values to those of conventional Pt employed CE.

Properties of Dye Sensitized Solar Cells with Porous TiO2 Layers Using Polymethyl-Methacrylate Nano Beads

We prepared polymethyl methacrylate (PMMA) beads with a particle size of 80 nm to improve the energy conversion efficiency (ECE) by increasing the effective surface area and the dye absorption ability of the working electrodes (WEs) in a dye sensitized solar cell (DSSC). We prepared the TiO2 layer with PMMA beads of 0.0~1.0 wt%; then, finally, a DSSC with 0.45 cm2 active area was obtained. Optical microscopy, transmission electron microscopy, field emission scanning electron microscopy, and atomic force microscopy were used to characterize the microstructure of the TiO2 layer with PMMA. UV-VIS-NIR was used to determine the optical absorbance of the WEs with PMMA. A solar simulator and a potentiostat were used to determine the photovoltaic properties of the PMMA-added DSSC. Analysis of the microstructure showed that pores of 200 nm were formed by the decomposition of PMMA. Also, root mean square values linearly increased as more PMMA was added. The absorbance in the visible light regime was found to increase as the degree of PMMA dispersion increased. The ECE increased from 4.91% to 5.35% when the amount of PMMA beads added was increased from 0.0 to 0.4 wt%. However, the ECE decreased when more than 0.6 wt% of PMMA was added. Thus, adding a proper amount of PMMA to the TiO2 layer was determined to be an effective method for improving the ECE of a DSSC.

Diffusion of the High Melting Temperature Element from the Molten Oxides for Copper Alloys

To alloy high melting point elements such as boron, ruthenium, and iridium with copper, heat treatment was performed using metal oxides of , , and at the temperature of in vacuum for 30 minutes. The microstructure analysis of the alloyed sample was confirmed using an optical microscope and FE-SEM. Hardness and trace element analyses were performed using Vickers hardness and WD-XRF, respectively. Diffusion profile analysis was performed using D-SIMS. From the microstructure analysis results, crystal grains were found to have formed with sizes of 2.97 mm. For the copper alloys formed using metal oxides of , , and the sizes of the crystal grains were 1.24, 1.77, and 2.23 mm, respectively, while these sizes were smaller than pure copper. From the Vickers hardness results, the hardness of the Ir-copper alloy was found to have increased by a maximum of 2.2 times compared to pure copper. From the trace element analysis, the copper alloy was fabricated with the expected composition. From the diffusion profile analysis results, it can be seen that 0.059 wt%, 0.030 wt%, and 0.114 wt% of B, Ru, and Ir, respectively, were alloyed in the copper, and it led to change the hardness. Therefore, we verified that alloying of high melting point elements is possible at the low temperature of .