Stark Spectroscopy of Absorption and Emission of Indoline Sensitizers: A Correlation with the Performance of Photovoltaic Cells

Electric field effects on photoexcitation dynamics and electronic properties of highly efficient indoline sensitizers, DN488, D205, and DN182, embedded in PMMA films have been examined by using electroabsorption (E-A) and electrophotoluminescence (E-PL) spectroscopic techniques and time-resolved photoluminescence (PL) decay measurements in the presence of electric fields. Photovoltaic performances have been also measured for devices constructed using these sensitizers. Then, field-induced quenching of PL and field-induced change in PL decay profile were observed, and it was found that these field effects, which depend on the sensitizers investigated herein, are well correlated with the trend of power conversion efficiencies of the corresponding photovoltaic cells. Electric dipole moment and molecular polarizability of these sensitizers both in the ground state (S-0) and in the excited state have been calculated at the level of B3LYP/6-31G(d), and the differencesof these physical parameters between So and excited state thus obtained have been compared with the ones determined from the E-A and E-PL spectra. The present study of Stark spectroscopy of indoline dyes provides new insights for the exciton dissociation property and carrier mobility of organic dyes, which are important factors to understand the operation mechanism in dye-sensitized solar cells.