Efficient Organic Dye‐Sensitized Solar Cells: Molecular Engineering of Donor–Acceptor–Acceptor cationic dyes

Abstract

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 %.

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.…”

“…[60] No substantial differences weref ound within the thiophene derivatives PTZ2-6,w ith oxidation potentials being within ar ange of 120 mV,i na greement with literature data on similar compounds. [28][29][30][31] This suggestst hat the presence of different thiophene spacers andr ing substituents did not significantly affect the oxidation potential, and thust he HOMO energy level, of the corresponding dyes. This is in agreement with the spacer character of the thiophene moieties in the donor-p-acceptor dyes, rather than on the donor nature represented by the PTZ core.…”

“…In the H 2 productiono ver2 0h,t he new thiophenebased sensitizers revealed improved stabilityafter longerirradiation times and enhanced performances, in terms of H 2 productionr ates and light-to-fuel efficiencies,a fter an initial activation period, which weref or the first time associated with enhanced stability under photocatalytic production of H 2 and the absence of critical dye degradation. [21][22][23][24][25][26][27] Triggered by recent studies on phenothiazine (PTZ) derivatives as DSSC sensitizers [28][29][30][31] and by their first uses as light harvesters in the photo-driven productiono fH 2 , [32][33][34] we decided to systematically investigate this promising class of dyes by designing as eries of organic sensitizers containing the PTZ core as ad onor scaffold in donor-p-acceptor molecules. [14] Metal-freeo rganic sensitizers have gained an increasing role in the scientific literature of H 2 production, [15][16][17] with record DSSC powerc onversione fficiencies (PCE) exceeding1 2%.…”

“…[18][19][20] These dyes carry important advantages over metal complexes, such as easier and cheaper synthesis and purification, larger structural variety, and wider tunability of optical and energetic properties,w hich are fundamental to optimize the corresponding solar devices. [21][22][23][24][25][26][27] Triggered by recent studies on phenothiazine (PTZ) derivatives as DSSC sensitizers [28][29][30][31] and by their first uses as light harvesters in the photo-driven productiono fH 2 , [32][33][34] we decided to systematically investigate this promising class of dyes by designing as eries of organic sensitizers containing the PTZ core as ad onor scaffold in donor-p-acceptor molecules. Interestingly, av ery recent report on ac lass of benzo[b]phenothiazines confirms the increasing relevance of dye-sensitized H 2 production using organic dyes and PTZ derivatives.…”

Homo‐ and Heterodimeric Dyes for Dye‐Sensitized Solar Cells: Panchromatic Light Absorption and Modulated Open Circuit Potential

“…There were specific anchoring groups that promote the interfacial charge transfer from dye to TiO 2 that avoids the charge injection overpotential . Further V oc can be increased by the uplifted shift of TiO 2 conduction band, which is generated by sensitizer by developing its intrinsic electrostatic potential or dipole moment ,. Self organization of sensitizers on the {101} facet of the anatase TiO 2 is another important factor that diminish the device performance .…”