Porphyrins Containing a Triphenylamine Donor and up to Eight Alkoxy Chains for Dye-Sensitized Solar Cells: A High Efficiency of 10.9%

Abstract

Porphyrins are promising DSSC sensitizers due to their structural similarity to chlorophylls as well as their tunable strong absorption. Herein, a novel D-π-A porphyrin dye XW14 containing a strongly electron-donating triphenylamine moiety as the electron donor was designed and synthesized. To avoid undesirably decreased Voc caused by dye aggregation effect, two methoxy or hexyloxy chains were introduced to the para positions of the triphenylamine moiety to afford XW15 and XW16, respectively. To further extend the absorption to a longer wavelength, a benzothiadiazole unit was introduced as an auxiliary acceptor to furnish XW17. Compared with XW14, the introduction of additional methoxy or hexyloxy groups in XW15 and XW16 red-shift the onset wavelengths from 760 to 780 and 790 nm, respectively. More impressively, XW17 has a more extended π-conjugation framework, and thus, it exhibits a much broader IPCE spectrum with an extremely red-shifted onset wavelength of 830 nm, resulting in the highest Jsc (18.79 mA cm(-2)). On the other hand, the hexyloxy chains are favorable for suppressing the dye aggregation effect, and thus XW16 shows the highest Voc of 734 mV. As a result, XW16 and XW17 demonstrate photovoltaic efficiencies of 9.1 and 9.5%, respectively, higher than those of XW14 (8.6%) and XW15 (8.7%), and obviously higher than that of 7.94% for our previously reported dye, XW4. On the basis of optimized porphyrin dye XW17, we used a nonporphyrin dye with a high Voc and strong absorption around 500 nm (WS-5) as the cosensitizer to improve the Voc from 700 to 748 mV, with synergistical Jsc enhancement from 18.79 to 20.30 mA cm(-2). Thus, the efficiency was dramatically enhanced to 10.9%, which is among the highest efficiencies obtained for the DSSCs based on traditional iodine electrolyte. In addition, the DSSCs based on XW17 + WS-5 exhibit good photostability, which is beneficial for practical applications.

An Experimental and Theoretical Investigation of the Electronic Structures and Photoelectrical Properties of Ethyl Red and Carminic Acid for DSSC Application

“…Besides, Karlsson and coworkers [13] synthesized and tested a series of metal-free organic dyes with a core phenoxazine chromophore as sensitizers in DSSCs, and the results indicated that a dye with a furan-conjugated linker showed a shorter lifetime relative to dyes with the acceptor group directly attached to the phenoxazine. In addition, natural dyes such as chlorophylls [17,18,19], flavonoids [20,21], anthocyanins [22,23], and carotenoids [24,25] have also been applied to the research and development of DSSC owing to their environmental friendliness, relative abundance, easy preparation, and large absorption coefficients’ invisible region [26,27]. Kumara et al [28] reported the research of black tea waste extract (BTE) as a potential sensitizer, and the DSSC sensitized with pigment complexes of BTE showed a PCE of 0.20%, while a significant increase (η = 0.46%) was observed when the pH of the pigment solution was lowered.…”

Near‐Infrared‐Absorbing Metal‐Free Organic, Porphyrin, and Phthalocyanine Sensitizers for Panchromatic Dye‐Sensitized Solar Cells

“…XW17 on co‐sensitization with organic dye WS‐5 (see Ref. for structure) led to an impressive J SC of 20.3 mA cm −2 and an overall PCE of 10.9 % owing to an enhanced IPCE response in the 500–600 nm range . Dyes incorporating a thiophene π‐spacer between a BTD acceptor and carboxylic acid anchor and a directly substituted arylamine group on the porphyrin exhibited a stabilized ground‐state oxidation potential (LCVC02) .…”

Role of Co‐Sensitizers in Dye‐Sensitized Solar Cells

“… Molecular structures of porphyrin sensitizers XW1/XW2/XW3/XW4, XW14/XW15/XW16, XW17, XW9/XW10/XW11, and XW22/XW24 reported by Xie and co‐workers.…”

“…In addition, the long alkyl chain on the auxiliary acceptor in the D–A–π–A co‐sensitizer (WS‐5) hindered charge recombination, resulting in high V OC (774 mV) and PCE of 10.41 % (XW4+WS‐5). The absorption was further extended to longer wavelengths with various substituents introduced onto the porphyrin dyes (XW14–XW17, Figure ) . DSSCs exhibit V OC values for co‐sensitized XW14–XW17+WS‐5 (748–773 mV) higher than the individual dyes (700–734 mV) with synergistic enhancement of J SC from 17.07 to 20.30 mA cm −2 .…”