Electron Transfer at Dye-sensitized Solar Cells. 2.

QEq-CS Theory and Estimation of IPCE Tendency

Abstract

In order to estimate IPCE (Incident Photon-to-Current Conversion Efficiency) of DSSC (dye-Sensitized Solar Cells), we constructed a theory and established a calculation procedure. The electron transfer rate constant consists of free energy change and electron transfer integral between the states before and after the electron transfer. We estimate both values by QEq-CS (Charge Equilibration for Charge Separation) method. Using experimental data of DSSC with 9-phenyl xanthene dye (Sayama et al. Chem.Lett. 753 (1998)) as the target, we studied three electron transfer steps: (i) Step1, from the ground state of dye to semiconductor; (ii) Step 2, from iodine redox pair in the solution to the oxidized dye; (iii) Step 1', from the excited state of dye to semiconductor. We calculated the change of electrostatic energy, estimated the change of free energy, and calculated the activation factor with the reorganization energy related to the each step. As a result, we clarified that the activation factor of the Step 1' roughly explained the tendency of the IPCE for the dye-sensitized solar cells.