Effect of the Number of Anchoring and Electron-Donating Groups on the Efficiency of Free-Base- and Zn-Porphyrin-Sensitized Solar Cells

Abstract

A series of porphyrin compounds, free base (H2P) and their Zn (II) metallated analogues (ZnP), bearing one, two or three carboxylic acid groups, have been synthesized, characterized, and used as sensitizers in dye sensitized solar cells (DSSCs). The performance of these devices has been analyzed, showing higher efficiencies of those sensitized with ZnP compounds. These results have been explained, on one hand, taking into account the electronic character of the metal ion, which acts as mediator in the injection step, and, on the other, considering the number of anchoring groups, which determines both the stereoelectronic character of the dye and the way it binds to TiO2 surface.

Synthesis and Photovoltaic Performance of β-Amino-Substituted Porphyrin Derivatives

“…This improvement can be attributed to an increase of approximately 160 mV in V oc (1.8-fold increase) and of 1.6 mA cm −2 in the J sc value (7.8-fold increase). Large enhancements in DSSC efficiency upon Zn metalation in porphyrins have been attributed to a mediator role of the metal ion in the injection step [ 36 ]. The closed-shell nature of the Zn(II) ion with empty coordination sites can allow for a rapid injection of photoexcited porphyrin electrons into the TiO 2 conduction band, reflected in the high increase in J sc in 5c when compared to 5b .…”

“…Porphyrins 2b or 4 (50 mg) were added to solutions of 3-sulfanylbenzoic acid or 4sulfanylbenzoic acid (14.5 mg, 94 µmol, 1.5 eq.) in DMF (4 mL) and K 2 CO 3 (36…”

“…The mixtures were stirred at room temperature for 2 h or 8 h. Compounds 5a,b and 6a,b were obtained after precipitation from dichloromethane/methanol. 5a:36.8 mg, 63% yield; 5b: 43.2 mg, 74% yield; 6a: 43.3 mg, 74% yield; 6b: 40.3 mg, 69% yield. 5a: 1 H NMR (300 MHz, DMSO-d 6 , 40 • C): δ −2.81 (s, 2H, NH), 7.31 (d, 2H, J = 8.4 Hz), 7.62-7.70 (m, 3H), 7.78-7.85 (m, 10H), 7.92 (d, 2H, J = 8.4 Hz), 8.09-8.12 (m, 2H), 8.18-8.22 (m, 6H), 8.29 (s, 1H, NH), 8.62 (d, 1H, J = 4.9 Hz, β-H), 8.73-8.85 (m, 5H, β-H).…”

Unraveling Structure–Performance Relationships in Porphyrin-Sensitized TiO2 Photocatalysts

“…Additionally, the orientation of the porphyrin rings could be controlled with the number of substituents [ 39 , 80 , 81 ]. In this line, Ambre et al evaluated the number of carboxyl units attached to TiO 2 in a series of Zn porphyrins with an increasing number of meta - or para -carboxyphenyl anchoring groups [ 80 ].…”

“…A common strategy in this direction consists in effectively achieving the separation of the photogenerated carriers and preventing electron consumption through the undesired recombination of electrons and holes. This can be attained with a D–A structure [ 38 ], creating a strong dipole moment and an important push–pull effect, which rapidly drives the migration of electrons toward TiO 2 upon illumination [ 39 ]. At the same time, following this strategy, the injected electron life is extended [ 40 ], leading to an increase in photocatalytic activity and a higher quantum efficiency.…”