Efficient Solar Cells Based on Porphyrin Dyes with Flexible Chains Attached to the Auxiliary Benzothiadiazole Acceptor: Suppression of Dye Aggregation and the Effect of Distortion

Abstract

Donor-π-acceptor-type porphyrin dyes have been widely used for the fabrication of efficient dye-sensitized solar cells (DSSCs) owing to their strong absorption in the visible region and the ease of modifying their chemical structures and photovoltaic behavior. On the basis of our previously reported efficient porphyrin dye XW11, which contains a phenothiazine-based electron donor, a π-extending ethynylene unit, and an auxiliary benzothiadiazole acceptor, we herein report the syntheses of novel porphyrin dyes XW26-XW28 by introducing one or two alkyl/alkoxy chains into the auxiliary acceptor. The introduced chains can effectively suppress dye aggregation. As a result, XW26-XW28 show excellent photovoltages of 700, 701, and 711 mV, respectively, obviously higher than 645 mV obtained for XW11. Nevertheless, the optimized structures of XW26 and XW27 exhibit severe distortion, showing large dihedral angles of 57.2° and 44.0°, respectively, between the benzothiadiazole and benzoic acid units, resulting from the steric hindrance between the benzoic acid unit and the neighboring alkyl/alkoxy chain on the benzothiadiazole unit, and thus blue-shifted absorption, decreased photocurrents. and low efficiencies of 5.19% and 6.42% were observed for XW26 and XW27, respectively. Interestingly, XW26 exhibits a more blue-shifted absorption spectrum relative to XW27, indicating that the steric hindrance of the alkyl/alkoxy chains has a more pronounced effect than the electronic effect. Different from XW26 and XW27, XW28 contains only one alkyl chain neighboring the ethynylene unit, which does not induce obvious steric hindrance with the benzoic acid unit, and thus distortion of the molecule is not seriously aggravated compared with XW11. Hence, its absorption spectrum and photocurrent are similar to those of XW11. As a result, a higher efficiency of 9.12% was achieved for XW28 because of its suppressed dye aggregation and higher photovoltage. It is worth noting that a high efficiency of 10.14% was successfully achieved for XW28 upon coadsorption with CDCA, which is also higher than the corresponding efficiency obtained for XW11. These results provide a novel approach for developing efficient porphyrin dyes by introducing chains into the suitable position of the auxiliary benzothiadiazolyl moiety to suppress dye aggregation, without seriously aggravating distortion of the dye molecules.

Synthesis, Spectral, Electrochemical and Photovoltaic Studies of A3B Porphyrinic Dyes having Peripheral Donors

“…[22] Indoline substituted porphyrin dyes are reported to yield PCE conversion efficiency upto 10 %. [20,32,33] Recently, a new set of push-pull zinc porphyrin sensitizers revealed an impressive PCE of 13-14 %. This brings out the significance of structural modification of the dyes to alleviate dye aggregation.…”

Solar Cells Sensitized with Porphyrin Dyes Containing Oligo(Ethylene Glycol) Units: A High Efficiency Beyond 12 %

“…A screen‐printed double‐layer of TiO 2 particles was used as the photoelectrode. The detailed procedure was reported in our previous work . The films were then immersed into a 0.2 m m solution of the dyes in a mixture of toluene and ethanol (1:4, v / v ) for 10 h at room temperature.…”

“…The films were then immersed into a 0.2 m m solution of the dyes in a mixture of toluene and ethanol (1:4, v / v ) for 10 h at room temperature. The counter electrode was also prepared according to the procedure reported in our previous work . The composition of the electrolyte for fabricating the DSSCs was: 0.1 m LiI, 0.05 m I 2 , 0.6 m 1‐methyl‐3‐propyl‐imidazolium iodide (PMII), and 0.5 m 4‐ tert ‐butylpyridine (TBP) in acetonitrile.…”

“…Among these dyes, porphyrins have the advantages of having structures that are easy to modify and outstanding light‐harvesting ability . Therefore, many donor–π–acceptor (D–π–A)‐type zinc porphyrins with outstanding efficiencies have been synthesized . Although many of the highly efficient DSSCs have been fabricated based on a Co 3+ /Co 2+ electrolyte, it is still desirable to develop efficient DSSCs based on the traditional I − /I 3 − electrolyte because of the simple cell fabrication procedure .…”

An Efficient Aniline‐Based Co‐Sensitizer for High Performance N3‐Sensitized Solar Cells

“…In fact, DSSCs based on sensitization of a mesoporous TiO 2 using Ruthenium polypyridyl complexes attracted considerable interest among the researchers because of their good photophysical and electrochemical properties . However, there are several detrimental factors influencing the photovoltaic performance of the cells such as light havesting efficiency, dye aggregation and electron recombination resistance . In order to address these issues, several approaches are being attempted for the development of DSSCs with improved performance.…”