A Molecular Engineering Strategy of Phenylamine-Based Zinc-Porphyrin Dyes for Dye-Sensitized Solar Cells: Synthesis, Characteristics, and Structure–Performance Relationships

Abstract

The molecular engineering of phenylamine- and phenothiazine-based porphyrin dyes is an advisable strategy for high-efficiency dye-sensitized solar cells (DSSC). Herein, we incorporated two and three phenothiazine units into the triphenylamine donor (D) unit of porphyrin dye (T-1) to replace the benzene units, resulting in two novel porphyrin dyes, T-3 and T-4. UV–vis absorption studies revealed that the molar extinction coefficients (ε) on TiO2 films of T-3 and T-4 were significantly higher than T-1, mainly owing to the increased loaded amount. Hence, the T-3- and T-4-devices exhibit higher IPCE and Jsc values. Furthermore, transient PL measurements and electrochemical impedance spectroscopy (EIS) results demonstrate that the electron injection efficiency (ηinj) and electron lifetime (τ) of the T-3-device were the highest. Thus, the T-3-device achieved the highest power conversion efficiency (PCE) of 8.02% (N719, 8.45%) with V oc = 670 mV, J sc = 16.84 mA cm–2, and FF = 70.02%. Meanwhile, the theoretical calculation studies suggest the smaller dihedral angle between the D unit and porphyrin macrocycle of T-3, leading to a favorable intramolecular charge transfer (ICT) process (t = 1.831, q ct = 0.922) compared to that of T-4. These results demonstrate that introducing a different number of phenothiazine units to replace the benzene units of triphenylamine in suitable positions can serve as an effective strategy for developing efficient DSSC.

Novel D–A−π–A Organic Dyes with Phenoxazine as a Donor Unit for Dye-Sensitized Solar Cells: The Effect of an Ethynyl Group on Performance

“…Therein, the phenoxazine unit possesses excellent electron donor capacity due to its heterocyclic and 3D butterfly structure comprising electron-rich N and O heteroatoms. , In addition, its structure prevents molecular aggregation and benefits the hole transport abilities. Besides, it contains multiple active sites, which provides unlimited ideas for the design and synthesis of diversified new electronic units. − Sun et al designed and synthesized a series of novel phenoxazine-based dyes and achieved satisfactory photoelectric conversion efficiency. ,,− Moreover, our group has also carried out extensive research on POZ-based metal-free organic DSSC, ,− and applied it as a D unit to porphyrin dyes for the first time and achieved excellent performance . Our studies proved that the POZ unit has great potential for DSSC dyes as an electron-donating unit.…”

“…The diversity of the D unit makes the designing of dye molecular for DSSC more selective. To date, various kinds of electron-rich units including aromatic amine, indole, carbazole, phenothiazine, phenoxazine, and so on − have been reported. Therein, the phenoxazine unit possesses excellent electron donor capacity due to its heterocyclic and 3D butterfly structure comprising electron-rich N and O heteroatoms. , In addition, its structure prevents molecular aggregation and benefits the hole transport abilities.…”

Unraveling Structure–Performance Relationships in Porphyrin-Sensitized TiO2 Photocatalysts

“…The use of diarylamino groups as the “push” element in D–π–A porphyrin sensitizers together with the remarkable influence on photovoltaic performance triggered an intense activity to determine the effect of the number and the position of these substituents and search for alternative electron-donating groups (EDG) as replacements. In this field, Li et al recently proposed the use of phenothiazine donor groups instead of benzene units in the original triphenylamine group ( Figure 23 ) [ 99 ].…”

“… Molecular structures of porphyrin dyes showing increasingly bulky groups at the donor substituent. Reproduced from reference [ 99 ] with permission from the American Chemical Society, copyright 2021. …”

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

“…Representative techniques in this respect include perovskite solar cells, − organic solar cells, − and dye-sensitized solar cells (DSSCs). − Among them, DSSCs have attracted intensive attention as an eco-friendly, readily fabricated, and relatively efficient technique. 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 .…”