Woohyung Cho

Synergistic Catalytic Effect of a Composite (CoS/PEDOT:PSS) Counter Electrode on Triiodide Reduction in Dye-Sensitized Solar Cells

Inorganic/organic nanocomposite counter electrodes comprised of sheetlike CoS nanoparticles dispersed in polystyrenesulfonate-doped poly(3,4-ethylenedioxythiophene (CoS/PEDOT:PSS) offer a synergistic effect on catalytic performance toward the reduction of triiodide for dye-sensitized solar cells (DSSCs), yielding 5.4% power conversion efficiency, which is comparable to that of the conventional platinum counter electrode (6.1%). The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry measurements revealed that the composite counter electrodes exhibited better catalytic activity, fostering rate of triiodide reduction, than that of pristine PEDOT: PSS electrode. The simple preparation of composite (CoS/PEDOT:PSS) electrode at low temperature with improved electrocatalytic properties are feasible to apply in flexible substrates, which is at most urgency for developing novel counter electrodes for lightweight flexible solar cells.

A PEDOT-reinforced exfoliated graphite composite as a Pt- and TCO-free flexible counter electrode for polymer electrolyte dye-sensitized solar cells

Herein, we have demonstrated a highly efficient, flexible, and low-cost (Pt-free and TCO-free) counter electrode made of a highly conductive poly(3,4-ethylene dioxythiophene) (PEDOT)/exfoliated graphite (EFG) composite in solid state dye-sensitized solar cells (DSSCs) employing polymer electrolytes. Electropolymerized one-dimensional PEDOT nanofibers were firmly attached to a flexible EFG sheet affording high catalytic activity and electron conductivity. PEDOT/EFG counter electrode-based DSSCs showed an energy conversion efficiency of 5.7% with a solid polymer electrolyte, which is significantly higher than conventional Pt electrodes (4.4%) under similar device architecture conditions.

Toward Higher Energy Conversion Efficiency for Solid Polymer Electrolyte Dye-Sensitized Solar Cells: Ionic Conductivity and TiO2 Pore-Filling.

Even though the solid polymer electrolyte has many intrinsic advantages over the liquid electrolyte, its ionic conductivity and mesopore-filling are much poorer than those of the liquid electrolyte, limiting its practical application to electrochemical devices such as dye-sensitized solar cells (DSCs). Two major shortcomings associated with utilizing solid polymer electrolytes in DSCs are first discussed, low ionic conductivity and poor pore-filling in mesoporous photoanodes for DSCs. In addition, future directions for the successful utilization of solid polymer electrolytes toward improving the performance of DSCs are proposed. For instance, the facilitated mass-transport concept could be applied to increase the ionic conductivity. Modified biphasic and triple-phasic structures for the photoanode are suggested to take advantage of both the liquid- and solid-state properties of electrolytes.

Successful demonstration of an efficient I-/(SeCN)2 redox mediator for dye-sensitized solar cells

A new I(-)/(SeCN)(2) redox mediator has favorable properties for dye-sensitized solar cells (DSCs) such as less visible light absorption, higher ionic conductivity, and downward shift of redox potential than I(-)/I(3)(-). It was then applied for DSCs towards increasing energy conversion efficiency, giving a new potential for improving performance.

Efficient binary organic thiolate/disulfide redox mediators in dye-sensitized solar cells based on a carbon black counter electrode

New thiolate/disulfide redox couples (M−/M2) were introduced and also combined with T−/T2, resulting in more efficient binary redox couples. The binary redox couples, in particular M−/T2, yielded a high energy conversion efficiency and reasonably stable performance with the carbon black counter electrode for dye-sensitized solar cells.

Precise Morphology Control and Continuous Fabrication of Perovskite Solar Cells Using Droplet-Controllable Electrospray Coating System

Herein, we developed a novel electrospray coating system for continuous fabrication of perovskite solar cells with high performance. Our system can systemically control the size of CH3NH3PbI3 precursor droplets by modulating the applied electrical potential, shown to be a crucial factor for the formation of perovskite films. As a result, we have obtained pinhole-free and large grain-sized perovskite solar cells, yielding the best PCE of 13.27% with little photocurrent hysteresis. Furthermore, the average PCE through the continuous coating process was 11.56 ± 0.52%. Our system demonstrates not only the high reproducibility but also a new way to commercialize high-quality perovskite solar cells.

Room Temperature Synthesis of Highly Compact TiO2 Coatings by Vacuum Kinetic Spraying to Serve as a Blocking Layer in Polymer Electrolyte-Based Dye-Sensitized Solar Cells

Vacuum kinetic spraying (VKS) was used to form a blocking layer (BL) in order to increase the efficiency of dye-sensitized solar cells. Nano-sized TiO2 powders were deposited on fluorine-doped tin oxide (FTO) glass while varying the coating parameters including the mass flow, substrate transverse speed, and number of coating passes in order to control the thickness of the BL. Compared to the cell without a BL, the open-circuit voltage and short-circuit current density of the solar cell with a VKS-coated BL were noticeably improved. Consequently, the photoconversion efficiency increased up to 5.6%, which is significantly higher than that of a spin-coated BL.

Ruthenium(II) quasi-solid state dye sensitized solar cells with 8% efficiency using a supramolecular oligomer-based electrolyte

We have achieved 8% efficiency for the ruthenium(II) dye, SY-04, in quasi-solid state dye sensitized solar cells using a supramolecular oligomer-based electrolyte. The dyes in this study, SY-04 and SY-05, which were synthesized through highly efficient synthetic routes, showed better molar extinction coefficients compared to that of the Z907 dye. In the absorption spectra, SY-04 and SY-05 displayed better red shifted metal ligand charge transfer (MLCT) absorption bands at 533, 382 and 535, 373 nm, respectively, compared with 521, 371 nm of the Z907 dye. Also, SY-04 and SY-05 showed better molar extinction coefficients, 6691, 16189 M−1 cm−1 and 6694, 16195 M−1 cm−1 as compared with the Z907 dye, 4308, 4917 M−1 cm−1. When excited into the charge-transfer absorption bands of SY-04 and SY-05 in ethanol at 77 K, broad emission bands for SY-04 and SY-05 with a maximum at 788 nm and 786 nm, respectively, were observed compared to the emission band of Z907 at 797 nm. The current–voltage characteristics of the SY-04 sensitizer gave the best performance data, JSC = 18.0 mA cm−2, VOC = 0.662 V, ff = 0.663, and an η of 8.0%. The increased VOC value for SY-04 than Z907 is mainly attributed to high charge recombination resistance by effective dye coverage, which is confirmed by impedance spectroscopy.

TiO2 surface engineering with multifunctional oligomeric polystyrene coadsorbent for dye-sensitized solar cells

Oligomeric, hydrophobic coadsorbents based on polystyrene (o-PS, Mn = 2600) terminated by a carboxylic acid exhibit dual functions in dye-sensitized solar cells (DSCs): suppression of electron recombination at the TiO2 surface, and enhanced concentration of the strongly-anchored dye, N719, which has two carboxylic acid groups. Engineering the TiO2 surface via o-PS results in the concurrent and significant enhancement of photovoltage and photocurrent, consequently increasing the energy conversion efficiency of DSCs by as much as 28.7%. The electron recombination rate was largely reduced via the blockage of vacant sites with o-PS chains on the TiO2 surface due to the physical hindrance to I3−s in electrolyte. In addition, the formation of the o-PS:I2 charge transfer complex at the photoanode/electrolyte interface lessened the effective concentrations of free I3− and/or I2 for electron recombination. Upon sequential o-PS coadsorption, the concentration of the strongly-anchored dyes on the TiO2 surface was increased via deprotonation of the weakly-anchored dyes, giving rise to an increase in the electron injection efficiency and, subsequently, the overall power conversion efficiency. The dual functions of the o-PS coadsorbent have been therefore demonstrated to increase the overall efficiency of DSCs.