Five organic dyes with pyridine-N-oxide as the anchor group and electron acceptor have been synthesized and applied in dye-sensitized solar cells (DSSCs). Benzothiadiazole was introduced in the conjugation system to increase the electron withdrawing properties, FTIR spectra showed that the coordination was between the pyridine-N-oxide and the Brønsted acid site on the TiO₂ surface. The relationship between different dye structures and the performance of the DSSCs was investigated systematically. The location of the thiophene unit was studied, and the direct linkage of benzothiadiazole with pyridine-N-oxide was beneficial to broaden the absorption. The donor–acceptor–acceptor-configured dye WL307, which has 2-ethylhexyloxy chains in the donor part, showed the best efficiency of 6.08 % under 100 mW cm⁻² light illumination. The dye series showed a fairly good stability during the one month test period.

Novel cyanine dyes, in which a tetrahydroquinoline derivative is used as an electron donor and 1-butyl-5-carboxy-3, 3-dimethyl-indol-1-ium moiety is used as an electron acceptor and anchoring group, were designed and synthesized for application in dye-sensitized solar cells. The photovoltaic performance of these solar cells depends markedly on the molecular structure of the dyes in terms of the n-hexyl chains and the methoxyl unit. Retardation of charge recombination caused by the introduction of n-hexyl chains resulted in an increase in electron lifetime. As a consequence, an improvement of open-circuit photovoltage (V_oc) was achieved. Also, the electron injection efficiencies were improved by the introduction of methoxyl moiety, which led to a higher short-circuit photocurrent density (J_sc). The highest average efficiency of the sensitized devices (η) was 5.6 % (J_sc=13.3 mA cm⁻², V_oc=606 mV, and fill factor FF=69.1 %) under 100 mW cm⁻² (AM 1.5G) solar irradiation. All of these dyes have very high absorption extinction coefficients and strong absorption in a relatively narrow spectrum range (500–650 nm), so one of our organic dyes was explored as a sensitizer in co-sensitized solar cells in combination with the other two other existing organic dyes. Interestingly, a considerably improved photovoltaic performance of 8.2 % (J_sc=20.1 mA cm⁻², V_oc=597 mV, and FF=68.3 %) was achieved and the device showed a panchromatic response with a high incident photon-to-current conversion efficiency exceeding 85 % in the range of 400–700 nm.

Organic dyes have become widely used in dye-sensitized solar cells (DSSCs) because of their good performance, flexible structural modifications, and low costs. To increase the photostability of organic dye-based DSSCs, we conducted a full study on the degradation mechanism of cyanoacrylic acid-based organic sensitizers in DSSCs. The results showed that with the synergy between water and UV light, the sensitizer could desorb from the TiO₂ surface and the cyanoacrylic acid unit of the sensitizer was transformed into the aldehyde group. It was also observed that the water content had a great effect on the degradation process. Our experiments conducted using ¹⁸O-labeled water demonstrated that the oxygen atom of the aldehyde group identified in the degraded dye came from the solvent water in the DSSCs. Therefore, controlling the water content during DSSC fabrication, good sealing of cells, and filtering the UV light are crucial to produce DSSCs that are more durable and robust.

Three metal-free donor–acceptor–acceptor sensitizers with ionized pyridine and a reference dye were synthesized, and a detailed investigation of the relationship between the dye structure and the photophysical and photoelectrochemical properties and the performance of dye-sensitized solar cells (DSSCs) is described. The ionization of pyridine results in a red shift of the absorption spectrum in comparison to that of the reference dye. This is mainly attributable to the ionization of pyridine increasing the electron-withdrawing ability of the total acceptor part. Incorporation of the strong electron-withdrawing units of pyridinium and cyano acrylic acid gives rise to optimized energy levels, resulting in a large response range of wavelengths. When attached to TiO₂ film, the conduction band of TiO₂ is negatively shifted to a different extent depending on the dye. This is attributed to the electron recombination rate between the TiO₂ film and the electrolyte being efficiently suppressed by the introduction of long alkyl chains and thiophene units. DSSCs assembled using these dyes show efficiencies as high as 8.8 %.

Four new type II organic dyes with D-π-A structure (donor-π-conjugated-acceptor) and two typical type II sensitizers based on catechol as reference dyes are synthesized and applied in dye sensitized solar cells (DSCs). The four dyes can be adsorbed on TiO₂ through hydroxyl group directly. Electron injection can occur not only through the anchoring group (hydroxyl group) but also through the electron-withdrawing group (CN) located close to the semiconductor surface. Experimental results show that the type II sensitizers with a D-π-A system obviously outperform the typical type II sensitizers providing much higher conversion efficiency due to the strong electronic push-pull effect. Among these dyes, LS223 gives the best solar energy conversion efficiency of 3.6%, with J_sc=7.3 mA·cm⁻², V_oc=0.69 V, FF=0.71, the maximum IPCE value reaches 74.9%.

New hemicyanine dyes (CM101, CM102, CM103, and CM104) in which tetrahydroquinoline derivatives are used as electron donors and N-(carboxymethyl)-pyridinium is used as an electron acceptor and anchoring group were designed and synthesized for dye-sensitized solar cells (DSSCs). Compared with corresponding dyes that have cyanoacetic acid as the acceptor, N-(carboxymethyl)-pyridinium has a stronger electron-withdrawing ability, which causes the absorption maximum of dyes to be redshifted. The photovoltaic performance of the DSSCs based on dyes CM101–CM104 markedly depends on the molecular structures of the dyes in terms of the n-hexyl chains and methoxyl. The device sensitized by dye CM104 achieved the best conversion efficiency of 7.0 % (J_sc=13.4 mA cm⁻², V_oc=704 mV, FF=74.8 %) under AM 1.5 irradiation (100 mW cm⁻²). In contrast, the device sensitized by reference dye CMR104 with the same donor but the cyanoacetic acid as the acceptor gave an efficiency of 3.4 % (J_sc=6.2 mA cm⁻², V_oc=730 mV, FF=74.8 %). Under the same conditions, the cell fabricated with N719 sensitized porous TiO₂ exhibited an efficiency of 7.9 % (J_sc=15.4 mA cm⁻², V_oc=723 mV, FF=72.3 %). The dyes CM101–CM104 show a broader spectral response compared with the reference dyes CMR101–CMR104 and have high IPCE exceeding 90 % from 450 to 580 nm. Considering the reflection of sunlight, the photoelectric conversion efficiency could be almost 100 % during this region.

A series of novel metal-free organic dyes TC301–TC310 with relatively high HOMO levels were synthesized and applied in dye-sensitized solar cells (DSCs) based on electrolytes that contain Br⁻/Br₃⁻ and I⁻/I₃⁻. The effects of additive Li⁺ ions and the HOMO levels of the dyes have an important influence on properties of the dyes and performance of DSCs. The addition of Li⁺ ions in electrolytes can broaden the absorption spectra of the dyes on TiO₂ films and shift both the LUMO levels of the dyes and the conduction band of TiO₂, thus leading to the increase of J_sc and the decrease of V_oc. Upon using Br⁻/Br₃⁻ instead of I⁻/I₃⁻, a large increase of V_oc is attributed to the enlarged energy difference between the redox potentials of electrolyte and the Fermi level of TiO₂, as well as the suppressed electron recombination. Incident photon to current efficiency (IPCE) action spectra, electrochemical impedance spectra, and nanosecond laser transient absorption reveal that both the electron collection yields and the dye regeneration yields (Φ_r) depend on the potential difference (the driving forces) between the oxidized dyes and the Br⁻/Br₃⁻ redox couple. For the dyes for which the HOMO levels are more positive than the redox potential of Br⁻/Br₃⁻ sufficient driving forces lead to the longer effective electron-diffusion lengths and almost the same efficient dye regenerations, whereas for the dyes for which the HOMO levels are similar to the redox potential of Br⁻/Br₃⁻, insufficient driving forces lead to shorter effective electron-diffusion lengths and inefficient dye regenerations.

Novel electrogenerated chemiluminescence (ECL) reagents C1, C2, and C3 with high fluorescence quantum yields bearing 15-crown-5 moiety have been synthesized and characterized. The photophysical, electrochemical, and ECL characters of these compounds have been studied in a 1:1 (v/v) PhH/MeCN mixed solvent. The ECL intensity is enhanced distinctly with the increase in the fluorescence quantum yield. Their ECL behaviors have been studied using annihilation and co-reactant methods (tri-n-propylamine (TPrA) was used as a co-reactant), respectively. The stable ECL emissions of compounds C1–C3 can be ascribed to the typical and simple monomer ECL emission via S-route. Copyright © 2008 John Wiley & Sons, Ltd.

A novel dye (2TPA-R), containing two triphenylamine (TPA) units connected by a vinyl group and rhodanine-3-acetic acid as the electron acceptor, is designed and synthesized successfully to reveal the working principles of organic dye in dye-sensitized solar cells (DSSCs). 2TPA and TPA-R, which consist of two TPA units connected by vinyl and a TPA unit linked with rhodanine-3-acetic acid, respectively, are also synthesized as references to study the intramolecular energy transfer (E_nT) and charge transfer (ICT) processes of 2TPA-R in CH₂Cl₂ solution and on a TiO₂ surface. The results suggest that the intramolecular E_nT and ICT processes show a positive effect on the performance of DSSCs. However, the flexible structure and less-adsorbed amount of dye on TiO₂ may make it difficult to improve the efficiency of DSSCs. This study on intramolecular E_nT and ICT processes acts as a guide for the design and synthesis of efficient organic dyes in the future.