Fuling Guo

Stable Dyes Containing Double Acceptors without COOH as Anchors for Highly Efficient Dye-Sensitized Solar Cells†

The electron acceptor 2-(1,1-dicyanomethylene) rhodanine is a promising alternative to cyanoacrylic acid as an anchoring group for organic dyes. For example, the RD-II-based dye-sensitized solar cell has an overall conversion efficiency of 7.11 % and long-term stability.

Series of new D-A-π-A organic broadly absorbing sensitizers containing isoindigo unit for highly efficient dye-sensitized solar cells.

In this work, six new D-A-π-A sensitizers (ID1-ID6), with triarylamine as the electron donor; isoindigo as a auxiliary electron withdrawing unit; thiophene, furan, and benzene as the linker; and cyanoacrylic acid as the anchoring group, were synthesized through simple synthetic procedures and with low cost. Their absorption spectra were broad with long wavelength absorption maximum approximately at 589 nm and the absorption onset at 720 nm on the TiO(2) film. Electrochemical experiments indicate that the HOMO and LUMO energy levels can be conveniently tuned by alternating the donor moiety and the linker. All of these dyes performed as sensitizers for the DSSCs test under AM 1.5 similar experimental conditions, and a maximum overall conversion efficiency of 5.98% (J(sc) = 14.77 mA cm(-2), V(oc) = 644 mV, ff = 0.63) is obtained for ID6-based DSSCs when TiO(2) films were first immersed for 6 h in 20 mM CDCA ethanol solution followed by 12 h of dipping in the dye CH(2)Cl(2) solution. Electrochemical impedance measurement data implies that the electron lifetime can be increased by coadsorption of CDCA, which leads to a lower rate of charge recombination and thus improved V(oc).

Benzotriazole-bridged sensitizers containing a furan moiety for dye-sensitized solar cells with high open-circuit voltage performance.

Two new benzotriazole-bridged sensitizers are designed and synthesized (BTA-I and BTA-II) containing a furan moiety for dye-sensitized solar cells (DSSCs). Two corresponding dyes (BTA-III and BTA-IV) with a thiophene spacer were also synthesized for comparison. All of these dyes performed as sensitizers for DSSCs, and the photovoltaic performance data of these benzotriazole-bridged dyes showed a high open-circuit voltage (V(oc): 804-834 mV). Among the four dyes, DSSCs based on BTA-II, with a furan moiety and branched alkyl chain, showed the highest V(oc) (834 mV), a photocurrent density (J(sc)) of 12.64 mA cm(-2), and a fill factor (FF) of 0.64, corresponding to an overall conversion efficiency (η) of 6.72%. Most importantly, long-term stability of the BTA-I-IV-based DSSCs with ionic-liquid electrolytes under 1000 h light-soaking was demonstrated, and BTA-II exhibited better photovoltaic performance of up to 5.06% power conversion efficiency.

New Bithiazole-Based Sensitizers for Efficient and Stable Dye-Sensitized Solar Cells

A series of new push-pull organic dyes (BT-I-VI), incorporating electron-withdrawing bithiazole with a thiophene, furan, benzene, or cyano moiety, as π spacer have been synthesized, characterized, and used as the sensitizers for dye-sensitized solar cells (DSSCs). In comparison with the model compound T1, these dyes containing a thiophene moiety between triphenylamine and bithiazole display enhanced spectral responses in the red portion of the solar spectrum. Electrochemical measurement data indicate that the HOMO and LUMO energy levels can be tuned by introducing different π spacers between the bithiazole moiety and cyanoacrylic acid acceptor. The incorporation of bithiazole substituted with two hexyl groups is highly beneficial to prevent close π-π aggregation, thus favorably suppressing charge recombination and intermolecular interaction. The overall conversion efficiencies of DSSCs based on bithiazole dyes are in the range of 3.58 to 7.51 %, in which BT-I-based DSSCs showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 81.1 %, a short-circuit photocurrent density (J(sc)) of 15.69 mA cm(-2), an open-circuit photovoltage (V(oc)) of 778 mV, and a fill factor (ff) of 0.61, which correspond to an overall conversion efficiency of 7.51 % under standard global AM 1.5 solar light conditions. Most importantly, long-term stability of the BT-I-III-based DSSCs with ionic-liquid electrolytes under 1000 h of light soaking was demonstrated and BT-II with a furan moiety exhibited better photovoltaic performance of up to 5.75 % power conversion efficiency.

Efficient and stable organic DSSC sensitizers bearing quinacridone and furan moieties as a planar π-spacer

In this work, three new quinacridone-based dyes containing a furan moiety (QA1–3) have been synthesized through simple synthetic routes for the application of dye-sensitized solar cells (DSSCs). Their absorption spectra, electrochemical, photovoltaic properties and the cell long-term stability have been extensively investigated. Electrochemical measurement data indicates that the tuning of the HOMO and LUMO energy levels can be conveniently realized by alternating the donor moiety. The theoretical calculations show that the dihedral angle between the quinacridone moiety and the furan ring is less than 1 degree, indicating excellent planarity between the two groups, which is beneficial for intramolecular charge transfer. All of these dyes performed as sensitizers for DSSCs tested under similar AM 1.5 experimental conditions, and a maximum solar energy to electricity conversion efficiency of 7.70% (Jsc = 13.25 mA cm−2, Voc = 804 mV, FF = 0.73) for the 20 mM chenodeoxycholic acid (CDCA) co-adsorbed DSSCs based on QA1 is obtained. Electrochemical impedance experiments indicate that the electron lifetime is improved by co-adsorption of CDCA, accounting for the significant improvement of Voc. Most importantly, the long-term stability of the QA1–3-based DSSCs with ionic-liquid electrolytes under 1000 h light-soaking has been demonstrated.

Photovoltaic performance of bithiazole-bridged dyes-sensitized solar cells employing semiconducting quantum dot CuInS2 as barrier layer material

In this work, the quantum dot CuInS2 layer was deposited on TiO2 film using successive ionic layer absorption and reaction (SILAR) method, and then two bithiazole-bridged dyes (BTF and BTB) were sensitized on the CuInS2/TiO2 films to form dye/CuInS2/TiO2 photoanodes for DSSCs. It was found that the quantum dots CuInS2 as an energy barrier layer not only could effectively improve open-circuit voltage (Voc) of solar cell, but also increase short-circuit photocurrent (Jsc) compared to the large decrease in Jsc of ZnO as energy barrier layer. The electrochemical impedance spectroscopy (EIS) measurement showed that the CuInS2 formed a barrier layer to suppress the recombination from injection electron to the electrolyte and improve open-circuit voltage. Finally, the open-circuit voltage increased about 22 and 27mV for BTF and BTB-/CuInS2/TiO2-based cells, the overall conversion efficiencies also reached to 7.20% and 6.74%, respectively.

Structure-property relationship of different electron donors: new organic sensitizers based on bithiazole moiety for high efficiency dye-sensitized solar cells

Three metal-free bithiazole organic dyes (BTT-I–III) based on D–A-π-A building blocks were designed and synthesized for dye-sensitized solar cells (DSSCs) to study the influence of different electron donors on photovoltaic properties, in which the electron donors of BTT-I–III were carbazole, triphenylamine and indoline moieties, respectively. The UV/Vis absorption spectra of BTT-III containing indoline as electron-donor displayed red-shifted absorption compared to the other two dyes with an onset close to 700 nm. The incident photon-to-current conversion efficiency (IPCE) spectra of BTT-III showed a wide region and kept a value higher than 10–15% during 580–650 nm. Electrochemical measurement data indicated that the HOMO and LUMO energy levels could be tuned through introducing different electron-donors in the dye molecule. It was found that the overall conversion efficiency of indoline donor based dye BTT-III showed the highest efficiency of 7.86% under AM 1.5 irradiation (100 mW cm−2). The electron lifetime calculated from electrochemical impedance spectroscopy (EIS) measurement demonstrated the reduced charge recombination and the higher open-circuit voltage.

EFFECT OF THIOPHENE IN BITHIAZOLE-BRIDGED SENSITIZERS ON THE PERFORMANCE OF DYE-SENSITIZED SOLAR CELLS

In this paper, we have designed and synthesized four bithiazole-bridged sensitizers (BT-T2, TBT-T2, BT-T3 and TBT-T3) with triphenylamine and indoline as the donor segment and applied them to dye-sensitized solar cells (DSSCs). For triphenylamine-based sensitizers as BT-T2 and TBT-T2, adding one thiophene unit between triphenylamine donor and bithiazole moiety not only led to bathochromic shift of the maximum absorption and increase of molar extinction coefficient, but also enhanced the photovoltaic conversion efficiency from 7.12% of BT-T2 to 7.51% of TBT-T2. But for indoline-based sensitizers as BT-T3 and TBT-T3, adding one thiophene unit between indoline donor and bithiazole moiety resulted in hypochromatic shift instead of bathochromic shift. We employed the density functional theory (DFT) calculations to further investigate the influence of the thiophene unit on their optical and electronic properties and photovoltaic performance of corresponding DSSC devices. Given the results, a reasonable explanation is the introduction of thiophene unit suppressed the intramolecular charge transfer and charge separation in the conjugation system of indoline-based sensitizer, which led to the hypochromatic shift of the maximum absorption wavelength and finally the low Jsc. Since the Jsc dropped sharply from 15.26 mAcm-2 to 4.52 mAcm-2, the photovoltaic conversion efficiency decreased dramatically from 7.86% to 1.93%.