Hexylthiophene‐Featured D–A–π–A Structural Indoline Chromophores for Coadsorbent‐Free and Panchromatic Dye‐Sensitized Solar Cells

Abstract

For a sensitizer with a strong π‐conjugation system, a coadsorbent is needed to hinder dye aggregation. However, coadsorption always brings a decrease in dye coverage on the TiO2 surface. Organic ‘‘D–A–π–A’’ dyes, WS‐6 and WS‐11, are designed and synthesized based on the known WS‐2 material for coadsorbent‐free, dye‐sensitized solar cells (DSSCs). Compared with the traditional D–π–A structure, these D–A–π–A indoline dyes, with the additional incorporated acceptor unit of benzothiadiazole in the π‐conjugation, exhibit a broad photoresponse, high redox stability, and convenient energy‐level tuning. The attached n‐hexyl chains in both dyes are effective to suppress charge recombination, resulting in a decreased dark current and enhanced open‐circuit voltage. Electrochemical impedance spectroscopy studies indicate that both the resistance for charge recombination and the electron lifetime are increased after the introduction of alkyl chains to the dye molecules. Without deoxycholic acid coadsorption, the power‐conversion efficiency of WS‐6 (7.76%) on a 16 μm‐thick TiO2 film device is 45% higher than that of WS‐2 (5.31%) under the same conditions. The additional n‐hexylthiophene in WS‐11 extends the photoresponse to a panchromatic spectrum but causes a low incident photon‐to‐current conversion efficiency.

Tuning Thiophene‐Based Phenothiazines for Stable Photocatalytic Hydrogen Production

“…The current-voltage (J-V)c urves and incident photon-to-current conversion efficiencies (IPCE, see Figure S3) showedt hat, with the exceptiono fPTZ6,p hotocurrent and corresponding PCE of the devices sensitized by the thiophene-based dyes were larger than the PTZ1-based DSSC (see Ta ble S1), in agreement with the enhanced opticalp roperties. These datao nt he photosensitizing and charge formation and collection properties indicatest he beneficiale ffects of the alkyl groups on the thiophene rings,i nt erms of suppressing recombination reactions as widely reported in the literature, [30,[62][63][64] with particular emphasis on the position of the substituents in the dye central moiety. Electrochemical impedance spectroscopy (EIS, see Figure S4) evidenced that this was attributed to its long electron lifetime, mainly associated to the larger contributiono ft he chemical capacitance.…”

Substituent effect of Ru(ii)-based sensitizers bearing a terpyridine anchor and a pyridyl azolate ancillary for dye sensitized solar cells

“…3(d)-(f). These observations are in sharp contrast with the increased efficiency observed for both organic D-A-D sensitizers [48][49][50] and zinc porphyrin sensitizers 51,52 with the benzothiadiazolyl unit located near the carboxy anchor. Upon increasing the thickness to 15 + 5 mm, the DSCs revealed signicantly improved current densities of 16.29 and 16.32 mA cm À2 and slightly lowered photovoltages of 787 and 777 mV, which are consistent with better light harvesting and a slightly reduced photovoltage; the latter is caused by the deteriorated coverage of the sensitizer that leads to faster electron recombination.…”

Metal-free organic dyes with benzothiadiazole as an internal acceptor for dye-sensitized solar cells

“…Mp 4.2.9. 3,6-Bis-{4-[2-(4-diphenylamino-phenyl)-vinyl]-phenyl}-9-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl-carbazole (9). A mixture of 8 (230 mg, 0.227 mmol), bis(pinacolato)diboron (144 mg, 0.567 mmol), PdCl 2 (dppf)$CH 2 Cl 2 (37 mg, 0.045 mmol), and potassium acetate (89 mg, 0.908 mmol) in 1,4-dioxane (25 mL) was refluxed for 24 h. After the reaction was complete, the solvent was removed under high vacuum and the residue was extracted with MC and water.…”

“…8 In this regard, the highly efficient organic dyes with D-A-p-A structures recently have been described; these incorporate an additional electron-withdrawing moiety, which affords several advantages, such as easy tuning of the molecular energy levels and bathochromic shifts of the absorption region, which improve photovoltaic performance. 9 Typical donor molecular structures are arylamine derivatives, such as triphenylamine or carbazole, which are well known for their strong electron-donating abilities. 10 Benzothiadiazole, 11 benzotriazole, 12 quinoxaline, 13 diketopyrrolopyrrole, 14 and nitro-cyanostilbene 15 are used as internal electron acceptor units.…”