Pyridomethene-BF2 complex/phenothiazine hybrid sensitizer with high molar extinction coefficient for efficient, sensitized solar cellsElectronic supplementary information (ESI) available: Synthetic procedures, Scheme S1-4, Fig. S1-8 and Table S1-2. See DOI: 10.1039/c5ta03807c

• Main Authors: Lin, Yan-Duo, Ke, Bo-Yu, Chang, Yuan Jay, Chou, Po-Ting, Liau, Kang-Ling, Liu, Ching-Yang, Chow, Tahsin J
• Format: Article
• Language: English
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c5ta03807c

A series of new pyridomethene-BF 2 /phenothiazine hybrid metal-free organic sensitizers K1-K8 containing different π-spacers were synthesized and applied in dye-sensitized solar cells (DSSC). The introduction of the pyridomethene-BF 2 complex unit to the phenothiazine chromophore resulted in a high molar extinction coefficient in favor of light harvesting. Quantum chemical calculations were performed using the density functional theory (DFT) at the B3LYP/6-31G(d,p) level to investigate the structural properties and electron density distributions of these dyes. The effect of dyes K1-K8 on the performance of DSSC was investigated systematically with comparisons to the plain phenothiazine dyes R1 and R2 . Upon co-adsorption with deoxycholic acid, the dye K3 , with a thiophene unit between the phenothiazine and pyridomethene-BF 2 units, exhibited the best photovoltaic performance. The short-circuit current density ( J sc ) was 15.43 mA cm −2 with an open-circuit voltage ( V oc ) of 0.69 V and a fill factor (FF) of 0.62, which correspond to a power-conversion efficiency ( η ) of 6.58% under AM 1.5G irradiation (100 mW cm −2 ). The n -hexyl chain attached to the thiophene in K4-K5 improved the V oc value. The presence of the phenyl pyridomethene-BF 2 moiety at the N(10) atom of phenothiazine in K6-K8 reduced π-π aggregation. These results reveal the advantage of incorporating a pyridomethene-BF 2 group in the dyes for high-performance DSSC cells. Organic dyes containing both phenothiazine and pyridomethene-BF 2 moieties displayed the highest power-conversion efficiency 6.58% under AM 1.5G irradiation condition.