Highly Twisted Dianchoring D-π-A Sensitizers for Efficient Dye-Sensitized Solar Cells

High-Performance Photocatalytic Hydrogen Generation Using Robust Dianchoring Photosensitizers

A novel series of donor-donor-π-acceptor (D-D-π-A) 9,9'-dihexylfluorene-based dianchoring organic dyes, each featuring distinct bridging electron-donating moieties, have been synthesized and characterized. Their performances in photocatalytic hydrogen evolution (PHE) were evaluated, taking into account of their photophysical and electrochemical attributes. Remarkably, (Z)-3-(5-(4-((4-(5-((E)-2-carboxy-2-cyanovinyl)thiophen-2-yl)phenyl)(9,9-dihexyl-9H-fluoren-2-yl)amino)phenyl)thiophen-2-yl)-2-cyanoacrylic acid achieved an active and robust H2 generation system with a turnover number (TON) of up to 17 400 in 126 h, with a production of 1090 μmol (26.3 mL) of hydrogen. The initial turnover frequency (TOFi), initial activity (activityi), and initial apparent quantum yield (AQYi) were 808 h-1, 505 mmol g-1 h-1, and 8.65%, respectively, under visible light irradiation in water. This photosensitizer is considered one of the most effective and durable systems for photocatalytic hydrogen production that attached to molecular Pt-TiO2, as stated out in the literature using organic dyes under visible light, when compared the TOF and TON values. The experimental results demonstrated that the dianchoring dyes with bridging units could significantly enhance PHE performance, maintaining justifiable durability over prolonged irradiation.

Unprecedented strong and reversible atomic orbital hybridization enables a highly stable Li–S battery

The shuttle effect and excessive volume change of the sulfur cathode severely impede the industrial implementation of Li–S batteries. It is still highly challenging to find an efficient way to suppress the shuttle effect and volume expansion. Here, we report, for the first time, an innovative atomic orbital hybridization concept to construct the hierarchical hollow sandwiched sulfur nanospheres with double-polyaniline layers as the cathode material for large-scale high-performance Li–S batteries. This hierarchically 3D, cross-linked and stable sulfur–polyaniline backbone with interconnected disulfide bonds provides a new type and strong intrinsic chemical confinement of sulfur owing to the atomic orbital hybridization of Li 2s, S 3p, C 2p and N 2p. Crucially, such atomic orbital hybridization of sulfur sandwiched in the double sulfur–polyaniline network is highly reversible during the discharge/charge process and can very efficiently suppress the shuttle effect and volume expansion, contributing to a very high capacity of 1142 mAh g^–1 and an excellent stabilized capacity of 886 mAh g^–1 at 0.2 C after 500 cycles with a suppressed volume expansion and an unprecedented electrode integrity. This innovative atomic orbital hybridization concept can be extended to the preparation of other electrode materials to eliminate the shuttle effect and volume expansion in battery technologies. The present work also provides a commercially viable and up-scalable cathode material based on this strong and highly reversible atomic orbital hybridation for large-scale high-performance Li–S batteries.

Effect of Extending the Conjugation of Dye Molecules on the Efficiency and Stability of Dye-Sensitized Solar Cells

We designed and synthesized two organic dyes (A6 and A10) for dye-sensitized solar cells (DSSCs) by extending the molecular conjugation strategy. The sensitizer A10 was constructed by inserting ethene into our previously reported sensitizer AZ6. The sensitizer A6 was obtained by further substituting the hydrogen of ethene with another donor (D) and π-bridge-acceptor (π-A) segment. The UV-vis spectra and J-V curves showed that the dyes A10 and A6 could effectively facilitate the light-harvesting and photocurrent densities with respect to AZ6. Consequently, the A10-based DSSC achieved an enhanced efficiency (8.54%) with a high photocurrent (18.81 mA cm^-2). Desorption experiments of dyes adsorbed on TiO₂ showed that compared with the monoanchoring dyes AZ6 and A10, the dianchoring configuration effectively strengthened the affinity of dye A6 with the photoanode, making it more difficult to leach from the photoanode. The A6-based DSSC shows outstanding stability, and its overall efficiency could remain 98.0% of its initial value after 3000 h of aging time, exceeding that of its monoanalogue AZ6 (remained 78.3% after 3000 h).

Effect of π-Conjugated Spacer in N-Alkylphenoxazine-Based Sensitizers Containing Double Anchors for Dye-Sensitized Solar Cells

A series of novel double-anchoring dyes for phenoxazine-based organic dyes with two 2-cyanoacetic acid acceptors/anchors, and the inclusion of a 2-ethylhexyl chain at the nitrogen atom of the phenoxazine that is connected with furan, thiophene, and 3-hexylthiophene as a linker, are used as sensitizers for dye-sensitized solar cells. The double-anchoring dye exhibits strong electronic coupling with TiO₂, provided that there is an efficient charge injection rate. The result showed that the power conversion efficiency of DP-2 with thiophene linker-based cell reached 3.80% higher than that of DP-1 with furan linker (η = 1.53%) under standard illumination. The photovoltaic properties are further tuned by co-adsorption strategy, which improved power conversion efficiencies slightly. Further molecular theoretical computation and electrochemical impedance spectroscopy analysis of the dyes provide further insight into the molecular geometry and the impact of the different π-conjugated spacers on the photophysical and photovoltaic performance.

Theoretical analysis of the absorption spectrum, electronic structure, excitation, and intramolecular electron transfer of D-A'-π-A porphyrin dyes for dye-sensitized solar cells

A series of porphyrin dyes with D-A'-π-A structure were designed and theoretically investigated by DFT and TD-DFT methods. Different electron-withdrawing auxiliary acceptor units were introduced into the dye molecule skeleton to shed light on how the type and position of auxiliary acceptors influence the photoelectric performance of the dyes. It was found that the introduction of electron-withdrawing units, BTD, TPZ, BTZ, PP and DPPZ, between the Zn-porphyrin core and the anchoring group had a significantly positive influence on the performance of the dye molecules. Also, more appropriate electron distribution in the molecular orbital and the lower HOMO-LUMO energy gap, more extensive absorption coverage, higher light-harvesting efficiency, lower orbital overlap, and more effective long-range intramolecular electron transfer (IET) process can be achieved as compared to the reference dye. Among these five electron-withdrawing units, BTD and TPZ had the effect leading to the greatest improvement and therefore, are the best candidates for auxiliary acceptors. The calculated results indicated that the longitudinal π-conjugation of the electron-withdrawing unit also had an obvious effect on the performance of the dye molecule, and NTD is expected to be a more effective auxiliary acceptor than BTD. The effects of the relative positions of the auxiliary acceptors in the dye molecular skeleton were also investigated. A comparative study of AX1-3 and AA1-3 showed that the introduction of BTD, TPZ and BTZ units between the donor part and the Zn-porphyrin core may have a negative impact on the performance of the dyes. Our studies are expected to provide new insight for the design and screening of high-efficiency porphyrin dyes for DSSCs applications.

Tetraphenylethylene-bridged double-branched sensitizers featuring hetero-donors for dye-sensitized solar cells

Effects of hetero-donors on the photovoltaic performance of tetraphenylethylene-based organic dyes were systematically investigated.

Organic Sensitizers with Extended Conjugation Frameworks as Cosensitizers of Porphyrins for Developing Efficient Dye-Sensitized Solar Cells

Relatively high efficiencies have been achieved for porphyrin-based dye-sensitized solar cells. For the purpose of designing efficient cosensitizers, we herein report systematically optimized dyes XC1-XC5 employing a triphenylamine donor, a benzothiadiazole moiety as the auxiliary acceptor, and a benzoic acid acceptor. One hexyl and four hexyloxy groups were introduced, and an ethynylene moiety was introduced between the donor and the auxiliary acceptor to afford XC1. To further extend the absorption wavelength, a second ethynylene moiety was introduced between the acceptor and the auxiliary acceptor to afford XC2. XC3 and XC4 were designed by introducing one and two methyl substituents, respectively, into the meta-positions of the anchoring carboxyl group. XC5 was further synthesized by inserting a cyano substituent into one of the ortho-positions of the carboxyl group with the purpose to strengthen the intramolecular charge-transfer effect and thus broaden the absorption wavelength. As expected, compared with the J_sc (14.29 mA·cm^-2) of XC1, the corresponding J_sc values for XC2-XC5 were enhanced to 16.50, 16.95, 16.73, and 17.74 mA·cm^-2, respectively. Moreover, XC4 exhibits the highest V_oc of 770 mV owing to the presence of a maximum of seven chains, which can effectively suppress dye aggregation. As a result, compared with XC1, XC2-XC5 exhibit improved efficiencies of 8.67, 9.05, 8.78, and 9.30%, respectively. In addition, the efficiencies of XC3 and XC5 were further enhanced by cosensitizing them with our previously reported porphyrin dye XW28 under various conditions. Finally, a remarkable efficiency of 10.50% was achieved for the cells cosensitized with XC5 and XW28. These results indicate that the combination of good planarity of the extended D-π-A framework with multiple alkoxy/alkyl chains may compose an effective optimizing strategy for designing and synthesizing excellent cosensitizers for porphyrins.

Electron-Affinity-Triggered Variations on the Optical and Electrical Properties of Dye Molecules Enabling Highly Efficient Dye-Sensitized Solar Cells

The synthesis, characterization, and photovoltaic performance of a series of indacenodithiophene (IDT)-based D-π-A organic dyes with varying electron-accepting units is presented. By control of the electron affinity, perfectly matching energy levels were achieved with a copper(I/II)-based redox electrolyte, reaching a high open-circuit voltage (>1.1 V) while harvesting a large fraction of solar photons at the same time. Besides achieving high power conversion efficiencies (PCEs) for dye-sensitized solar cells (DSCs), that is, 11.2 % under standard AM 1.5 G sunlight, and 28.4 % under a 1000 lux fluorescent light tube, this work provides a possible method for the design and fabrication of low-cost highly efficient DSCs.

New D–π–A dyes incorporating dithieno[3,2-b:2′,3′-d]pyrrole (DTP)-based π-spacers for efficient dye-sensitized solar cells

Bulky substituents on the N-position of the DTP spacer optimize the photovoltaic performances of DSSCs.