Miao-Syuan Fan

Copper zinc tin sulfide as a catalytic material for counter electrodes in dye-sensitized solar cells

Quaternary Cu2ZnSnS4 (CZTS) semiconductor thin films, deposited onto an indium-doped tin oxide (ITO) conducting substrate by sulfurizing direct-current (DC) magnetron sputtered Cu–Zn–Sn metal alloys, were used as the counter electrode (CE) of dye-sensitized solar cells (DSSCs). X-ray diffraction (XRD) and Raman spectroscopy reveal that all the samples show the kesterite Cu2ZnSnS4 phase. The morphology becomes smoother for the Cu-rich or Zn-rich sample, as confirmed by atomic force microscopy (AFM) and field-emission scanning electron microscopy (FE-SEM). The influence of the [Cu]/[Zn] + [Sn] molar ratio in the CZTS samples on the catalytic performance of DSSCs was also investigated. The electrocatalytic ability and electrochemical properties of the CEs were studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel plots. The performance of DSSCs with various CEs was verified by J–V curves and incident photon-to-current conversion efficiency (IPCE) curves. The maximum solar-to-electrical power efficiency of DSSCs using CZTS as the CE approached 7.94%. These results showed the attractive potential of CZTS to replace the Pt CE (8.55%). The influence of different molar ratios of CZTS CEs on the DSSC performance is discussed in detail.

Benzimidazole-Branched Isomeric Dyes: Effect of Molecular Constitution on Photophysical, Electrochemical, and Photovoltaic Properties

Three benzimidazole-based isomeric organic dyes possessing two triphenylamine donors and a cyanoacrylic acid acceptor are prepared by stoichiometrically controlled Stille or Suzuki-Miyaura coupling reaction which predominantly occurs on the N-butyl side of benzimidazole due to electronic preferences. Combined with the steric effect of the N-butyl substituent, placement of the acceptor segment at various nuclear positions of benzimidazole such as C2, C4, and C7 led to remarkable variations in intramolecular charge transfer absorption, electron injection efficiency, and charge recombination kinetics. The substitution of acceptor on the C4 led to red-shifted absorption, while that on C7 retarded the charge transfer due to twisting in the structure caused by the butyl group. Because of the cross-conjugation nature and poor electronic interaction between the donor and acceptor, the dye containing triphenylamine units on C4 and C7 and the acceptor unit on C2 showed the low oxidation potential. Thus, this dye possesses favorable HOMO and LUMO energy levels to render efficient sensitizing action in solar cells. Consequently, it results in high power conversion efficiency (5.01%) in the series with high photocurrent density and open circuit voltage. The high photocurrent generation by this dye is reasoned to it exceptional charge collection efficiency as determined from the electron impedance spectroscopy.

Anthracene/Phenothiazine π-Conjugated Sensitizers for Dye-Sensitized Solar Cells using Redox Mediator in Organic and Water-based Solvents

Metal-free dyes (MD1 to MD5) containing an anthracene/phenothiazine unit in the spacer have been synthesized. The conversion efficiency (7.13 %) of the dye-sensitized solar cell using MD3 as the sensitizer reached approximately 85 % of the N719-based standard cell (8.47 %). The cell efficiency (8.42 %) of MD3-based dye-sensitized solar cells (DSSCs) with addition of chenodeoxycholic acid is comparable with that of N719-based standard cell. The MD3 water-based DSSCs using a dual-TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl)/iodide electrolyte exhibited very promising cell performance of 4.96 % with an excellent Voc of 0.77 V.