Solar cells sensitized with doubly concerted companion dyes with optimized donors to achieve high efficiencies up to 12.5%: a record efficiency for iodine electrolyte-based DSSCs†

Abstract

Fluorenyl indoline based electron donors have been employed in constructing DSSC dyes with high photocurrents. However, commonly used fluorenyl indoline donors possess two or fewer alkyl chains and thus suffer from serious dye aggregation and charge recombination, resulting in undesirable moderate open-circuit voltages (V_OC) in spite of high short-circuit current densities (J_SC). To enhance the V_OC and maintain high J_SC, we herein report the design and synthesis of a fluorenyl indoline donor substituted with a dihexyloxyphenyl moiety, and thus porphyrin dye XW93 and the corresponding doubly concerted companion (DCC) dyes XW94 and XW95 have been synthesized and used to fabricate DSSCs based on iodine electrolyte, achieving enhanced V_OC values of 734, 750 and 759 mV, respectively. Meanwhile, XW94 and XW95 exhibit a high IPCE plateau from 370 to 700 nm with onset wavelengths up to 820 nm, affording high J_SC values over 22 mA cm⁻² and relatively high power conversion efficiencies (PCEs) of 11.8% and 12.1%, respectively. To further improve the V_OC, XW96 was synthesized by replacing the fluorenyl indoline donor with a bulky phenothiazine donor. The resulting DSSCs afford a considerably elevated V_OC of 782 mV with the J_SC slightly lowered to 21.97 mA cm⁻². As a result of the excellent V_OC and satisfactory J_SC, the highest PCE of 12.5% has been achieved for XW96, which is the record efficiency for iodine electrolyte-based DSSCs, to the best of our knowledge. This work provides an effective approach for constructing high-performance DCC dyes based on optimized donors by combining the respective advantages of indoline and phenothiazine donors.