Baoqin Chen

Constructing organic D-A-π-A-featured sensitizers with a quinoxaline unit for high-efficiency solar cells: the effect of an auxiliary acceptor on the absorption and the energy level alignment.

Four organic D-A-π-A-featured sensitizers (TQ1, TQ2, IQ1, and IQ2) have been studied for high-efficiency dye-sensitized solar cells (DSSCs). We employed an indoline or a triphenylamine unit as the donor, cyanoacetic acid as the acceptor/anchor, and a thiophene moiety as the conjugation bridge. Additionally, an electron-withdrawing quinoxaline unit was incorporated between the donor and the π-conjugation unit. These sensitizers show an additional absorption band covering the broad visible range in solution. The contribution from the incorporated quinoxaline was investigated theoretically by using DFT and time-dependent DFT. The incorporated low-band-gap quinoxaline unit as an auxiliary acceptor has several merits, such as decreasing the band gap, optimizing the energy levels, and realizing a facile structural modification on several positions in the quinoxaline unit. As demonstrated, the observed additional absorption band is favorable to the photon-to-electron conversion because it corresponds to the efficient electron transitions to the LUMO orbital. Electrochemical impedance spectroscopy (EIS) Bode plots reveal that the replacement of a methoxy group with an octyloxy group can increase the injection electron lifetime by a factor of 2.4. IQ2 and TQ2 can perform well without any co-adsorbent, successfully suppress the charge recombination from TiO(2) conduction band to I(3)(-) in the electrolyte, and enhance the electron lifetime, resulting in a decreased dark current and enhanced open circuit voltage (V(oc)) values. By using a liquid electrolyte, DSSCs based on dye IQ2 exhibited a broad incident photon-to-current conversion efficiency (IPCE) action spectrum and high efficiency (η=8.50 %) with a short circuit current density (J(sc)) of 15.65 mA cm(-2), a V(oc) value of 776 mV, a fill factor (FF) of 0.70 under AM 1.5 illumination (100 mW cm(-2)). Moreover, the overall efficiency remained at 97% of the initial value after 1000 h of visible-light soaking.

Modulation of energy levels by donor groups: an effective approach for optimizing the efficiency of zinc-porphyrin based solar cells

In the design of efficient sensitizers for dye-sensitized solar cells (DSSCs), it is vital to modulate the HOMO and LUMO orbitals by introducing suitable donor and acceptor groups. In this respect, triphenylamine has been extensively used as the donor group. Porphyrin has strong absorption in the UV-Vis range, which makes it a promising dye candidate. In addition, a porphyrin molecule contains eight β positions and four meso-positions, which may be conveniently utilized for introducing multiple donor and acceptor moieties. In this work, various numbers of triphenylamine and trimethoxyphenyl groups are introduced to the porphyrin meso-positions as electron donors, with the aim to systematically modulate the energy levels and investigate the effect on the efficiency of the DSSCs. The HOMO–LUMO energy gaps remain almost constant irrespective of the donor groups, thus, the variation of the donors leads to a contradictory effect on the processes of electron injection and dye regeneration. In the case of the zinc porphyrin with two triphenylamine units and one trimethoxyphenyl group as the electron donors (M3T2P), moderate and well-matched HOMO and LUMO energy levels are observed, thus affording high efficiencies for both the electron injection and the dye regeneration processes. The overall conversion efficiencies (η) of the DSSCs based on these dyes lie in the range of 2.70–5.45%, with the optimized performance achieved by M3T2P, which can be rationalized by the efficient electron injection and dye regeneration processes, and the long electron lifetime, as demonstrated by the electrochemical impedance spectroscopy measurements. These results provide further insights into the strategy for elevating the efficiencies of DSSCs, especially those based on porphyrins, simply by modulating the electron donor groups.

A bis-boronic acid modified electrode for the sensitive and selective determination of glucose concentrations

A bis-boronic acid modified electrode for the sensitive and selective determination of glucose concentrations has been developed. The electrochemical characteristics of the sensor with added saccharides were investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The bis-boronic acid modified electrode was both sensitive and selective for glucose.

A microgap impedance sensor for the determination of trace water in organic solvents.

A microgap impedance sensor with a 50 μm gap was developed for the determination of trace water in organic solvents by coating poly(dimethyldiallylammonium chloride) (PDMDAAC) and ferricyanide/ferrocyanide composite materials on indium tin oxide (ITO). The electrochemical properties of the composite materials were investigated with cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). We observed that the impedance response of the sensor depended on the concentration of trace water in the organic solvents. Under optimized conditions, the linear range for the determination of trace water was 0-0.06% for chloroform (CHCl(3)), 0-0.10% for acetone (CH(3)COCH(3)), 0-0.12% for tetrahydrofuran (THF), and 0-0.10% for acetonitrile (CH(3)CN), and the detection limits were 0.65, 1.54, 0.61, and 1.72 ppm, respectively. The results obtained from the impedance sensors were comparable to those obtained using the traditional Karl Fischer method.