Investigation and design of efficient intramolecular charge transfer dyes with DBTP-based dual-electron-donor structure

Abstract

In this work, three recently synthesized D1-D2-π-A type dyes (DB-1/2/3) were regarded as the primary dyes and were theoretically investigated in the context of dye-sensitized solar cells (DSSCs). For each dye, a di (1-benzothieno)[3,2-b:2′,3′-d]pyrrole (DBTP) group (electron donor D2) functions as a dual-electron-donor together with another electron donor (D1). Through density functional theory and time-dependent density functional theory calculations, the ground-state information and the excited-state information was obtained to build structure-property connection for the dyes. In particular, the intramolecular charge transfer capacity was emphatically studied from multiple angles (via absorption spectra, frontier molecular orbitals, electron density difference, etc.). Some key parameters that affect the short-circuit current and the open-circuit voltage of DSSCs were calculated and compared. Finally, based on the primary dyes, four new D1-DBTP-π-A type dyes (D1/2/3/4) were designed with the aim of improving the performances of these type dyes. Our research theoretically explains why DB-1 characterized by a triphenylamine unit as D1 preforms better than the other two primary dyes experimentally. Furthermore, it is predicted that due to the best light-harvesting ability, the designed dye D4 with a coumarin unit as D1 is expected to surpass DB-1 and become the most promising and potential for DSSCs among all the dyes in this work.