Fluorenyl Indoline as an Efficient Electron Donor for Concerted Companion Dyes: Enhanced Light-Harvesting and Photocurrent

Abstract

Concerted companion dyes (CC dyes) like XW61 have been demonstrated to be an effective platform for developing efficient DSSCs. However, the moderated phenothiazine-based electron donor in XW61 results in unsatisfactory J sc. To address this problem, a stronger fluorenyl indoline-based electron donor has been used to construct porphyrin dye XW68 and organic dyes Y1–Y2. The stronger electron-donating character of the fluorenyl indoline unit leads to an enhanced J sc value (20.48 mA·cm–2) for the individual dye XW68. On this basis, CC dyes XW69–XW70-C8 have been designed and synthesized by combining the frameworks of Y1 and Y2 with XW68. The complementary absorption characters of the porphyrin and the organic dye moieties lead to panchromatic absorption with a strong light-harvesting capability from 350 to 700 nm and the onset wavelength extended to ca. 840 nm in the IPCE curves. As a result, excellent J sc values have been achieved (>22 mA·cm–2). In addition to the advantages of high J sc, bulky octyl groups have been introduced into the donor of XW70-C8 to reduce dye aggregation and suppress charge recombination. Finally, a highest PCE of 11.1% with a satisfactory J sc (22.25 mA·cm–2) and an enhanced V oc (750 mV) has been achieved upon coadsorption of XW70-C8 with CDCA. In addition, the CC dye XW70-C8-based solar cells exhibit excellent long-term photostability. These results provide an effective method for rationally improving the photovoltaic behavior, especially the J sc of CC dyes, by introducing strong electron donor moieties with suitable substituents.

Solar cells sensitized by donor-linked concerted companion dyes

“…37,38 Recently, we have developed a class of concerted companion (CC) dyes by covalently linking the organic dye and porphyrin dye units through flexible chains at the acceptor moieties. 15,[39][40][41] For example, XW76 has been constructed by linking the acceptors of two sub-dye units corresponding to XW10 and XL3 (Fig. 1a).…”

Efficient Dye-Sensitized Solar Cells Based on a New Class of Doubly Concerted Companion Dyes

“…As one of the core components of DSSCs, sensitizers are employed to harvest the sunlight and donate the excited electrons to the TiO 2 semiconductor. , Commonly used sensitizers include ruthenium dyes, − metal-free organic dyes, − and porphyrin dyes. − To develop high-performance sensitizers, panchromatic absorption is desired. However, obvious absorption defects are accompanied with distinct absorption peaks for most dyes. − To address this problem, two dyes with complementary absorption spectra can be used as cosensitizers to achieve panchromatic absorption and high-performance DSSCs. , However, it is challenging to optimize the ratio and distribution of the two adsorbed sensitizers on the TiO 2 film for such cosensitization approaches. − Hence, we recently developed “concerted companion dyes” XW60–XW63 (CC dyes, Figure a) by directly linking two subdye units with complementary absorption characters, which conveniently afforded panchromatic absorption and excellent photovoltaic performance as a consequence of the “intramolecular cosensitization” effect, without resorting to time-consuming optimization of the adsorption processes. − The double straps around the porphyrin macrocycles in these dyes can effectively suppress the aggregation of the porphyrin units, favorable for enhancing the V OC . However, these CC dyes only afforded moderate V OC values of ca.…”

Efficient Solar Cells Sensitized by Organic Concerted Companion Dyes Suitable for Indoor Lamps

“…In our previous work, CC dyes have been constructed by using a porphyrin unit as one of the components. [69,70] However, the large conjugation frameworks of porphyrin dyes lead to relatively severe dye-aggregation, which will quench the photoexcited dyes and thus cause energy loss. [71] Besides, the aggregation of porphyrins on the TiO 2 surface causes many vacancies to facilitate charge recombination.…”