Solar Cells Based on Doubly Concerted Companion Dyes with the Efficiencies Modulated by Inserting an Ethynyl Group at Different Positions

To develop efficient sensitizers for dye-sensitized solar cells (DSSCs), we recently reported doubly concerted companion (DCC) dye XW83 with a wrapped porphyrin sub-dye unit linked to an organic sub-dye unit through a flexible chain, which exhibits panchromatic absorption and excellent anti-aggregation ability. To further improve the absorption, we herein report XW87 and XW88 by inserting an ethynyl group into the organic sub-dye unit of XW83 near the donor and acceptor, respectively. For the corresponding organic dyes Z3 and Z4, the introduced ethynyl group improves their absorption, but induces aggravated charge recombination, leading to lowered power conversion efficiencies (PCEs). Similar to the organic dyes, the introduced ethynyl group improves the absorption of DCC dyes XW87 and XW88 as well. In addition, the ethynyl group near the acceptor of the organic sub-dye unit can be well protected by the long wrapping chains from the porphyrin unit. As a result, XW88 affords the highest JSC (21.84 mA/cm2), VOC (782 mV) and PCE (12.2%) among the DCC dyes. These results provide an effective method for developing efficient DSSC dyes by inserting an ethynyl group at a suitable position of a DCC dye.