Doubly strapped porphyrin improved efficiency from 8.6% to 9.3% and finally to 10.6% through a combined approach of coadsorption and cosensitization.

Photocurrent (J sc ) and photovoltage (V oc ) are two important parameters for dye-sensitized solar cells (DSSCs) to achieve high power conversion efficiencies (PCEs). Herein, we synthesize four novel porphyrin dyes, XW36−XW39, using an N-phenyl-substituted phenothiazine donor to pursue higher PCE. For XW36 and XW37, the N-phenyl group is wrapped with two ortho-alkoxy chains. In contrast, it is substituted with a para-alkoxy group in XW38 and XW39. The phenothiazine wrapping in XW36 and XW37 induces more serious distortion, which is beneficial for anti-aggregation but unfavorable for the electron transfer from donor to a porphyrin framework. Thus, individual porphyrin dyes XW36 and XW37 exhibit efficiencies of 9.05 and 9.58%, respectively, lower than those of 9.51 and 10.0% achieved for XW38 and XW39, respectively. Besides, the introduction of a methyl group into a benzoic acid acceptor unit is conducive to anti-aggregation and thus improves the V oc and efficiencies. Therefore, higher efficiencies were achieved for XW37 and XW39, compared with XW36 and XW38, respectively. Interestingly, although the individual XW36 dye shows a lowest efficiency among the four dyes, a highest efficiency of 11.7% was obtained for XW36 on the basis of synergetic adsorption with chenodeoxycholic acid and PT-C6 because of simultaneously improved J sc and V oc , which may be ascribed to the lowest dye-loading amount of XW36 among all of these porphyrin dyes, with the largest vacancy area left on the TiO 2 surface available for cosensitizer PT-C6, resulting in a highest J sc . The high efficiency of 11.7% is one of the highest efficiencies using I − /I 3 − electrolytes in DSSCs. These results provide an effective strategy for developing efficient DSSCs by the targeted coadsorption and cosensitization of porphyrin sensitizers optimized through introducing a bis(ortho-alkoxy)-wrapped phenyl group into the phenothiazine donor and/or methyl groups into the benzoic acid acceptor unit.

A series of new porphyrin dyes (XW42–XW44) containing oligo(ethylene glycol) units have been designed and synthesized. Two triethylene glycol units were introduced into the phenothiazine moiety of XW42, whereas diethylene glycol (DEG) and ethylene glycol chains were introduced to afford XW43 and XW44, respectively. Interestingly, the efficiencies of the DSSCs were clearly dependent on the chain lengths. Among the three dyes, XW42 and XW43 exhibited relatively high open‐circuit voltages of 751 and 750 mV, respectively, and XW43 exhibited the highest efficiency of 10.32 % owing to the presence of the DEG chains with suitable lengths and excellent ability to trap Li+. Furthermore, through a combined coadsorption and cosensitization approach, the efficiencies were dramatically enhanced. As a result, a highest efficiency of 12.10 % was obtained for the XW43+chenodeoxycholic acid+PT‐C6 (a metal‐free organic dye) system, which ranks among the highest efficiencies of cells based on the traditional iodine electrolyte.

To fabricate efficient dye-sensitized solar cells (DSSCs), 4-tertbutylpyridine (TBP) is commonly used as an additive in the electrolytes for improving the photovoltages (V OC ). However, TBP cannot play a positive role in improving the photocurrent (J SC ) because of the lack of absorption in the visible-wavelength range. We herein report a light-absorbing pyridine derivative N1 as an additive for the axial coordination with porphyrin dyes. N1 was synthesized by introducing a (bis(4-methoxyphenyl)amino)anthryl moiety into the para-position of pyridine via an acetylene bridge, and porphyrin dye XW64 containing meso-3,5-disubstituted phenyl groups was synthesized considering that the meta-substituted phenyl groups may induce weaker steric hindrance with the axial pyridyl ligand, as compared with wrapped and strapped porphyrin dyes. Thus, N1 was used as an electrolyte additive together with TBP. When optimized concentrations of 6 mM N1 and 0.5 M TBP were used for fabricating DSSCs based on XW64, enhanced photovoltaic performance was achieved, with J SC , V OC , and efficiency of 15.65 mA•cm −2 , 0.701 V, and 7.35%, respectively, superior to those of the corresponding DSSCs without using the additives (J SC = 14.86 mA•cm −2 , V OC = 0.599 V, and efficiency = 5.94%). The enhancement of J SC can be ascribed to the improved light-harvesting ability induced by the axially coordinated N1. Furthermore, the two additives also can be used to fabricate efficient solar cells based on the wrapped porphyrin dye XW42, achieving high efficiency of 10.3%, indicative of their general applicability in fabricating high-performance DSSCs. These results indicate that the simultaneous employment of the traditional TBP additive and a pyridyl ligand with light-harvesting ability in the electrolyte for the axial coordination to a porphyrin dye is a promising approach for developing efficient DSSCs.

No abstract