Jiangbin Xia

Influence of Doped Anions on Poly(3,4-ethylenedioxythiophene) as Hole Conductors for Iodine-Free Solid-State Dye-Sensitized Solar Cells

Poly(3,4-ethylenedioxythiophene) (PEDOT) is an excellent hole-conducting polymer able to replace the liquid I(-)/I3(-) redox electrolyte in dye-sensitized solar cells (DSCs). In this work we applied the in situ photoelectropolymerization technique to synthesize PEDOT and carried out a careful analysis of the effect of different doping anions on overall solar cell performance. The anions analyzed in this work are ClO4(-), CF3SO3(-), BF4(-), and TFSI(-). The best solar cell performance was observed when the TFSI(-) anion was used. Photoelectrochemical and impedance studies reveal that the doped anions in the PEDOT hole conductor system have great influences on I-V curves, conductivity, and impedance. The optimization of these parameters allowed us to obtain an iodine-free solid-state DSC with a maximum J(sc) of 5.3 mA/cm2, V(oc) of 750 mV, and a conversion efficiency of 2.85% which is the highest efficiency obtained so far for an iodine-free solid-state DSC using PEDOT as hole-transport material.

The influence of doping ions on poly(3,4-ethylenedioxythiophene) as a counter electrode of a dye-sensitized solar cell

Poly(3,4-ethylenedioxythiophene) (PEDOT) is an excellent kind of conducting polymer, comparable to Pt in catalytic behavior in dye-sensitized solar cells. Electrochemical polymerization in the presence of different anions (doping ions) that work as counterions of the resulting oxidized state PEDOT has been carried out to verify the influence of doping ions on the photo-electron conversion performance in dye-sensitized solar cells. Electrochemical and photo-electrochemical measurements reveal that the interaction between polymer and substrate (FTO) directly influences the fill factor in I–V curves, especially in the PEDOT–PSS system.

Application of polypyrrole as a counter electrode for a dye-sensitized solar cell

Conductive polymers have been widely applied as counter electrodes in dye-sensitized solar cells. However, as one of many materials in the conductive polymer family, polypyrrole attracts little attention in this field. In this paper, polypyrrole (PPy) was synthesized by vapour phase polymerization (VPP) and electropolymerization (EP) and these PPys were employed as counter electrodes in dye-sensitized solar cells. Comparing this to the regularly used Pt counter electrode, both of them show good catalytic behaviour in dye-sensitized solar cells though the PPy electrodes have a slightly lower fill factor. Such investigation will broaden the application of conductive polymers in DSCs. Our study indicates that polypyrrole is a good candidate to replace the Pt counter electrode in DSCs. Taking into consideration the regular solvent used in DSCs, it is recommended that an insoluble conductive polymer is a good choice for the counter electrode in DSCs.

Sputtered Nb2O5 as an effective blocking layer at conducting glass and TiO2 interfaces in ionic liquid-based dye-sensitized solar cells.

The thin Nb(2)O(5) layer works as a remarkable blocking layer when deposited by the rf magnetron sputtering method between fluorine-doped tin oxide and a mesoporous TiO(2) layer, improving open-circuit photovoltage (V(oc)) and fill factor (FF) with power conversion efficiency over 5.5% at 1 sun irradiation of the dye-sensitized TiO(2) solar cells using ionic liquid electrolytes.

Iodine-free quasi solid-state dye-sensitized solar cells based on ionic liquid and alkali salt

A novel iodine-free quasi solid-state electrolyte employing an ionic liquid (1, 2-dimethyl-3-propylimidazolium iodide, DMPII) as charge transfer intermediate was developed for dye-sensitized solar cells (DSSCs). Simultaneously, potassium iodide (KI) was incorporated into the electrolyte as charge transfer auxiliary agent. The dependences of photovoltaic performances and ionic conductivities on the iodine-free quasi solid-state electrolyte containing different KI concentrations were investigated. The strong interactions between the potassium cations and polyethylene oxide (PEO, MW = 100,000) can prevent the crystallization of the electrolyte and enhance its ionic conductivity. An optimal photoelectric conversion efficiency (η) of 5.87% can be obtained for the DSSC fabricated with the iodine-free electrolyte containing 5 wt% KI, and the corresponding value without KI is 4.05%, indicating the remarkable progress made by addition of KI into electrolyte.

Solid-state dye-sensitized solar cells fabricated by coupling photoelectrochemically deposited poly(3,4-ethylenedioxythiophene) (PEDOT) with silver-paint on cathode

A PEDOT-based dye-sensitized solar cell (DSC) is successfully improved by coupling photoelectrochemically deposited PEDOT layer with an Ag paste-paint on the cathode. With a 9.3 μm thick mesoscopic nanocrystalline TiO(2) film, a maximum cell performance of 3.2% with relatively high V(oc) of around 780 mV is achieved.

A novel ruthenium-free TiO2 sensitizer consisting of di-p-tolylaminophenyl ethylenedioxythiophene and cyanoacrylate groups

A novel ruthenium-free organic dye, 3-(5-(4-(di-p-tolylamino)styryl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-7-yl)-2-cyanoacrylic acid (coded as H01), is synthesized in a short sequence. The dye is composed of a di(p-tolyl)phenylamino moiety as an electron donor, a cyanoacrylate moiety as an electron acceptor, and an ethylenedioxythiophene unit as the spacer to bridge the donor and the acceptor. The as-prepared H01 dye is employed as a sensitizer in a dye-sensitized nanocrystalline TiO2 solar cell, and the short-circuit photocurrent density (Jsc), open-circuit voltage (Voc), and fill factor (ff) of the device under AM 1.5 (100 mW cm−2) irradiation, are 15.22 mA cm−2, 0.67 V, and 0.72, respectively, corresponding to an overall conversion efficiency (Eff) of 7.33%.

Synthesis and investigation of novel thiophene derivatives containing heteroatom linkers for solid state polymerization

Several thiophene derivatives containing different heteroatom linkers were rationally designed, synthesized and studied as potential candidates for solid state polymerization (SSP). Due to the flexible short single heteroatom linkers, these monomers may rotate freely under heating to meet the requirement needed for SSP. Meanwhile, our novel design strategy has been proved to be an amazing protocol and will pave the way to explore more systems in the polythiophene family by using such a facile SSP method.

Effect of flexible linker length in 3,4-ethylenedioxythiophene derivatives for solid state polymerization

Previously, we made a great breakthrough in solid state polymerization (SSP) for polythiophene by the new parallel design strategy of the introduction of a one-atom linker between the 3,4-ethylenedioxythiophene (EDOT) unit. Following this strategy, several EDOT derivatives with different lengths, by simply tuning the linker atoms number, were rationally designed, synthesized and studied as potential candidates for SSP. Now the question is raised here: does the flexible linker have a limited length for successful SSP? Here, we chose EDOT-linker-EDOT as a prototype monomer model due to its facile synthetic procedure and tunable flexible linker length. We examined up to a four-atom length and also investigated different halogen substituted effects. Detailed characterizations of their corresponding polymers were carried out and crystals of all the monomers were obtained for structures analysis. Our results reveal that the successful linker length of the monomers can be up to three atoms at least because the four-atom linker monomer failed to pass SSP due to its low melting point, though it has a preferred polymerization pathway according to the theoretical prediction based on its crystal structure. Moreover, the iodo-substituted monomer is inclined to form the corresponding polymer when compared with the bromo-substituted monomer. Furthermore, it is the first time that the molecule weight information of a polymer is obtained with the observation of its dependence on the temperature involved during the SSP. Our results are very important for fully understanding the SSP process, as well as for exploring monomer structures, for obtaining further rational design of new monomers and for tuning of the corresponding polymers properties.

Parallel design strategy and rational study of crystal engineering of novel 3,4-ethylenedioxythiophene derivatives for solid state polymerization

Several 3,4-ethylenedioxythiophene (EDOT) derivatives containing different heteroatom linkers were rationally designed along parallel directions. They were synthesized and studied as potential candidates for solid state polymerization (SSP). The detailed characterization of these corresponding polymers was carried out using UV-visible spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and several key crystal structures were analyzed. Our study reveals that heteroatoms like C, Si and P are good linkers between EDOT units, and most monomers can be spontaneously polymerized successfully by annealing at a moderate temperature. Due to the flexible short single heteroatom linkers, these monomers may rotate freely under heating, to meet the requirement for the success of SSP. By carefully analyzing typical crystal structures, direct evidence for the success of SSP was obtained for better understanding of the SSP process. In addition, effective Hal/Hal distance was defined and a new SSP model was proposed.