Poly(3,4-ethylenedioxythiophene) has been synthesized by common oxidation polymerization and employed as a standard counter electrode in dye-sensitized solar cell (DSSC). The relationship between PEDOT’s sheet resistance and their effect on DSSC is carefully investigated. The accurate controlling of PEDOT’s sheet resistance is simply tuned by hydrazine reduction or further iodine vapor oxidation. Our study reveals that the device’s open-circuit voltage (Voc) is almost independent with PEDOT’s sheet resistance, and the lower sheet resistance PEDOT has, the better fill factor (FF), short-circuit current density (Jsc) and performance solar cell devices can get. In addition, the re-oxidation by iodine vapor is an effective way to further improve DSSC performance.Poly (3,4-ethylenedioxythiophene) has been employed as a standard counter electrode in dye-sensitized solar cell (DSSC). The device’s open-circuit voltage (Voc) is almost independent with PEDOT’s sheet resistance and the lower sheet resistance PEDOT has, the better fill factor (FF), short-circuit current density (Jsc) and performance solar cell devices can get. The re-oxidation by iodine vapor is an effective way to further improve DSSC performance.Download high-res image (141KB)Download full-size image

•Pt//iFTO electrodes are prepared by a novel integrative method.•Pt//iFTO electrodes shows cell efficiency of 6.77%, which is a little higher than that of Pt//cFTO electrodes (6.70%).•This integrative method has advantages of rapid and facile processibility, accompanied by energy saving and greatly cost reduction.Conventional pyrolytic platinum loaded on commercial F-doped tin oxide (Pt//cFTO) conductive glass as counter electrode (CE) is a crucial component of DSSCs. In this paper, an integrative method was used to prepare platinum loaded on in-house-made iFTO glass (Pt//iFTO) without cFTO glass and the newly synthesized Pt//iFTO electrodes were applied as CEs in the DSCs. Compared with common Pt//cFTO electrode loading amount of Pt of 32.17 μg cm−2 which shows an efficiency of 6.70% as a CE in DSSCs, Pt//iFTO electrode loading less amount of Pt of 13.01 μg cm−2 still displays a slight higher cell efficiency of 6.77%. The integrative method requires simple equipment, easy operation, and discards the cFTO glass and significantly reduces costs. Meanwhile, Pt catalyst layer and iFTO substrate layer were formed at the same time in this method, saving a lot of thermal energy, which provides a new method for preparing electrodes needed high temperature post-processing.An integrative method was used to prepare platinum loaded on in-house-made iFTO glass (Pt//iFTO) without cFTO glass and the newly synthesized Pt//iFTO electrodes were applied as CEs in the DSCs. Compared with common Pt//cFTO electrode loading amount of Pt of 32.17 μg cm−2 which shows an efficiency of 6.70% as a CE in DSCs, Pt//iFTO electrode loading less amount of Pt of 13.01 μg cm−2 still displays a slight higher cell efficiency of 6.77%. The integrative method requires simple equipment, easy operation, and discards the cFTO glass and significantly reduces costs.Download high-res image (149KB)Download full-size image

Poly(3,4-ethylenedioxythiophene) (PEDOT) and thiophene based homopolymers were synthesized by self-acid-assisted polycondensation (SAAP) through mono-halogen substituted thiophene derivative monomers. Detailed characterization of the obtained polymers was carried out by X-ray diffraction (XRD), cyclic voltammetry (CV), infrared spectrum (IR), UV-Vis absorbance spectroscopy, fluorescence spectroscopy (FR) and thermogravimetric analysis (TGA). Most synthesized monomers can be spontaneously polymerized successfully through a simple annealing process at moderate temperature, indicating that they are suitable for SAAP. Moreover, our results reveal that substituted halogen (bromo or iodo) positions play an important role in SAAP, which may pave a wide path for exploring other conjugated polythiophenes through such a facile method.

Thieno[3,4-b]-1,4-dioxin, 5,5′-methylenebis[2,3-dihydro] was chosen as a universal solid state polymerization (SSP) platform due to its ready synthesis procedure, further tunable substitution groups on the CH2 bridge and its excellent conjugated quinonoid structure of corresponding poly(bis-3,4-ethylenedioxythiophene methine). These monomers were designed by taking the steric effect and molecular flexibility into consideration and by careful investigation under SSP. In addition, the aromatic moieties were firstly introduced in the branch chain in this polymer matrix, which may offer amazing properties and further modification opportunities based on this unique platform. Our results reveal that the substitution groups on the CH2 bridge play an important role in SSP. The bulkier the substitution group and the longer effective halogen distance the monomers have, the higher onset temperature (Tonset) the SSP will have. Furthermore, the primitive dependence of Tonset with an effective halogen distance was established.

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.

Based on an EDOT–CH2–N(R)–CH2–EDOT platform, we investigated the effect of the substituent on the nitrogen atom on solid-state polymerization. Detailed characterizations of the corresponding polymers were carried out and crystals of all the monomers were obtained for structural analysis. Our study revealed that the introduction of aromatic moieties makes SSP successful, which would greatly widen the scope of monomers. In addition, besides linker distance, the substitution on the CH2–N(R)–CH2 linker also plays an important role in the SSP behavior of monomers.

Two benzo(1,2-b:4,5-b′)dithiophene (denoted as BDT) based organic dyes, Dye 1 and Dye 2, containing triphenylamine and carbazole in the molecular frameworks respectively, were synthesized, characterized and applied in dye-sensitized solar cells (DSSCs). The photo-physical, photovoltaic, and electrochemical properties of the two dyes were analyzed in this work. The two dyes exhibit strong charge transfer absorption bands in the visible region. The dyes were applied in dye sensitized solar cells obtaining 11.34 mA/cm2, 0.75 V and 0.74, for the short-circuit photocurrent density (Jsc), open-circuit voltage (Voc), and fill factor (FF) respectively, corresponding to an overall power conversion efficiency of 6.3%. These results revealed that BDT-based dyes are promising dyes for DSSCs.Two organic dyes with benzo(1,2-b:4,5-b′)dithiophene (denoted as BDT) spacer have been prepared in combination with the triphenylamine and carbazole used as donor and the cyanoacrylic acid used as acceptor. And they exhibit up to 6% conversion efficiency based on regular liquid dye solar cell. Among them, the dye containing triphenylamine group shows the short-circuit photocurrent density (Jsc), open-circuit voltage (Voc), and fill factor (FF) of the device are 11.34 mA/cm2, 0.75 V, and 0.74, respectively, corresponding to an overall conversion efficiency of 6.3%.

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.

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.

An efficient plastic crystal-based electrolyte is prepared by employing succinonitrile as solid solvent and binary ionic liquids as charge transfer mediators for dye-sensitized solar cells (DSSCs). It was found that combining succinonitrile with ionic liquids could improve the mechanical property of electrolyte and avoid the fluidity of ionic liquid, and the fabricated solid-state solar cell shows an overall conversion efficiency of 2.14%, which can be further improved to 5.50% after optimizing the addition amount of lithium perchlorate (LiClO4) as charge transfer promoter into the plastic crystal electrolyte, and the role of LiClO4 in the plastic crystal ionic liquid electrolyte is evaluated through electrochemical and photoelectrochemical measurements. The knowledge obtained from this plastic crystal-based electrolyte exhibits new eyeshot to find solid-state electrolyte for DSSCs with high performance.Graphical abstractLiClO4 was incorporated into the iodine-free plastic crystal electrolyte to inhibit the crystallization of succinonitrile, and increase the charge transfer through enhancing charge exchange reaction between I−/I3−, therefore improve the conversion efficiency of DSSC.Highlights► Succinonitrile plastic crystal ionic liquid electrolyte was developed for solar cell. ► Succinonitrile can improve the mechanical property of ionic liquid electrolyte. ► Wiping out of I2 can avoid its light absorption and volatility. ► LiClO4 can promote the charge transfer of the plastic crystal-based electrolyte. ► Li+ ions can enhance the charge exchange between I−/I3− in the electrolyte.

•Poly(3,4-ethylenedioxythiophene) (PEDOT) can be obtained by acid-assisted polycondensation from 5-Bromo-2,3-dihydro-thieno[3,4-b][1,4]dioxine.•The generated hydrobromic acid can accelerate such polycondensation process.•Our research may broaden acid-assisted-polycondensation application among other monohalogen substituted thiophene-based derivatives.Poly(3,4-ethylenedioxythiophene) (PEDOT) can be obtained by acid-assisted polycondensation from 5-bromo-2,3-dihydro-thieno[3,4-b][1,4]dioxine. Detailed characterization of the obtained polymer was carried out by X-ray diffraction (XRD), Cyclic voltammetry (CV), Infrared spectrum (IR), UV–vis absorbance spectroscopy and Scanning Electron Microscopy (SEM). Because it may involve acid assisted mechanism, the generated hydrobromic acid can accelerate such polycondensation process. Moreover, according to the monomer's liquid feature and structure characterization, our research may broaden acid-assisted polycondensation application among other monohalogen substituted thiophene-based derivatives.

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.

A novel CuI-based iodine-free gel electrolyte using polyethylene oxide (PEO, MW = 100,000) as plasticizer and lithium perchlorate (LiClO4) as salt additive was developed for dye-sensitized solar cells (DSSCs). Such CuI-based gel electrolyte can avoid the problems caused by liquid iodine electrolyte and has relative high conductivity and stability. The effects of PEO and LiClO4 concentrations on the viscosity and ionic conductivity of the mentioned iodine-free electrolyte, as well as the performance of the corresponding quasi solid-state DSSCs were investigated comparatively. Experimental results indicate that the performance of DSSCs can be dramatically improved by adding LiClO4 and PEO, and there are interactions (Li+–O coordination) between LiClO4 and PEO, these Li+–O coordination interactions have important influence on the structure, morphology and ionic conductivity of the present CuI-based electrolyte. Addition of PEO into the electrolyte can inhibit the rapid crystal growth of CuI, and enhance the ion and hole transportation property owing to its long helix chain structure. The optimal efficiency (2.81%) was obtained for the quasi solid-state DSSC fabricated with CuI-based electrolyte containing 3 wt% LiClO4 and 20 wt% PEO under AM 1.5 G (1 sun) light illumination, with a 116.2% improvement in the efficiency compared with the cell without addition of LiClO4, indicating the promising application in solar cells of the present CuI-based iodine-free electrolyte.Highlights► A novel CuI-based iodine-free gel electrolyte for DSSC is firstly prepared. ► Such CuI-based electrolyte has relative high conductivity and stability. ► Addition amount of LiClO4 and PEO in the electrolyte is optimized. ► Cell performance is improved by 116.2% compared with the cell without LiClO4.

High work function material V2O5 with Al as a composite electrode is applied first as counter electrode in solid dye-sensitized solar cell (solid DSC). Such novel counter electrode gives over 2% conversion efficiency, which is comparable with noble Ag counter electrode. In addition, such novel electrode and concept would be widely used as counter electrode in other noniodine-based solid DSCs. The replacement of regular Au, Ag noble metal electrodes gives a way to reduce the cost of solid DSC in large scale production.Keywords: counter electrode; dye-sensitized; solid state; vanadium(V) oxide

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.