Porphyrins Containing a Triphenylamine Donor and up to Eight Alkoxy Chains for Dye-Sensitized Solar Cells: A High Efficiency of 10.9%

Abstract

Porphyrins are promising DSSC sensitizers due to their structural similarity to chlorophylls as well as their tunable strong absorption. Herein, a novel D−π–A porphyrin dye <b>XW14</b> containing a strongly electron-donating triphenylamine moiety as the electron donor was designed and synthesized. To avoid undesirably decreased <i>V</i>_oc caused by dye aggregation effect, two methoxy or hexyloxy chains were introduced to the <i>para</i> positions of the triphenylamine moiety to afford <b>XW15</b> and <b>XW16</b>, respectively. To further extend the absorption to a longer wavelength, a benzothiadiazole unit was introduced as an auxiliary acceptor to furnish <b>XW17</b>. Compared with <b>XW14</b>, the introduction of additional methoxy or hexyloxy groups in <b>XW15</b> and <b>XW16</b> red-shift the onset wavelengths from 760 to 780 and 790 nm, respectively. More impressively, <b>XW17</b> has a more extended π-conjugation framework, and thus, it exhibits a much broader IPCE spectrum with an extremely red-shifted onset wavelength of 830 nm, resulting in the highest <i>J</i>_sc (18.79 mA cm^–2). On the other hand, the hexyloxy chains are favorable for suppressing the dye aggregation effect, and thus <b>XW16</b> shows the highest <i>V</i>_oc of 734 mV. As a result, <b>XW16</b> and <b>XW17</b> demonstrate photovoltaic efficiencies of 9.1 and 9.5%, respectively, higher than those of <b>XW14</b> (8.6%) and <b>XW15</b> (8.7%), and obviously higher than that of 7.94% for our previously reported dye, <b>XW4</b>. On the basis of optimized porphyrin dye <b>XW17</b>, we used a nonporphyrin dye with a high <i>V</i>_oc and strong absorption around 500 nm (<b>WS-5</b>) as the cosensitizer to improve the <i>V</i>_oc from 700 to 748 mV, with synergistical <i>J</i>_sc enhancement from 18.79 to 20.30 mA cm^–2. Thus, the efficiency was dramatically enhanced to 10.9%, which is among the highest efficiencies obtained for the DSSCs based on traditional iodine electrolyte. In addition, the DSSCs based on <b>XW17</b> + <b>WS-5</b> exhibit good photostability, which is beneficial for practical applications