Molecular Engineering of Quinoxaline-Based D–A−π–A Organic Sensitizers: Taking the Merits of a Large and Rigid Auxiliary Acceptor

The continuing efforts of creating novel D–A−π–A structured organic sensitizers with excellent optoelectronic properties have resulted in substantial improvement of power conversion efficiency (PCE) as well as stability of dye-sensitized solar cells (DSSCs). Here, we report a new molecular engineering strategy for enhancing optical gain and improving excited-state features in D–A−π–A structured organic sensitizers by improving the conjugation size and rigidity of the auxiliary acceptor functional group. A series of phenanthrene-fused-quinoxaline (PFQ)-based D–A−π–A organic sensitizers (<b>WS-82</b>, <b>WS-83</b>, and <b>WS-84</b>) are designed and synthesized for applications in DSSCs. Compared to 2,3-diphenylquinoxaline (DPQ)-based dye <b>IQ-4</b>, PFQ dyes show extended absorption spectra and improved open-circuit voltage performance. Upon a systematical engineering of alkyl chains and π-spacer structure, the unfavorable issues of PFQ dyes including low solubility and high energy barrier in intramolecular charge transition are successfully eliminated. When applied in iodine electrolyte-based DSSCs, the best performing PFQ dye <b>WS-84</b> shows a PCE of 10.11%, which is much higher than that of our previous champion DPQ dye <b>IQ-4</b> under the same conditions