title: Coumarin dyes for dye-sensitized solar cells: A long-range-corrected density functional study.
abstract: The excited-state properties in a series of coumarin solar cell dyes are investigated with a long-range-corrected (LC) functional which asymptotically incorporates Hartree-Fock exchange. Using time-dependent density functional theory (TDDFT), we calculate excitation energies, oscillator strengths, and excited-state dipole moments in each of the dyes as a function of the range-separation parameter mu. To investigate the acceptable range of mu and to assess the quality of the LC-TDDFT formalism, an extensive comparison is made between LC-BLYP excitation energies and approximate coupled-cluster singles and doubles calculations. When using a properly optimized value of mu, we find that the LC technique provides a consistent picture of charge-transfer excitations as a function of molecular size. In contrast, we find that the widely used B3LYP hybrid functional severely overestimates excited-state dipole moments and underestimates vertical excitation energies, especially for larger dye molecules. The results of the present study emphasize the importance of long-range exchange corrections in TDDFT for investigating the excited-state properties in solar cell dyes.
authors.affiliation: Materials Chemistry Department, Sandia National Laboratories, Livermore, California 94551, USA. bmwong@sandia.gov
authors.forename: Bryan M
authors.initials: BM
authors.lastname: Wong
authors.forename: Joseph G
authors.initials: JG
authors.lastname: Cordaro