Dipole analyses for short-circuit current in organic photovoltaic devices of diketopyrrolopyrrole-based donor and PCBM

Guiding principles to design highly optimized organic photovoltaic devices that achieve high power conversion efficiencies (PCEs) are strongly desired. To obtain a useful guideline, we have investigated the photo- and electrochemical properties of four diketopyrrolopyr-role (DPP) derivatives containing double DPP blocks by ab initio calculations according to Yu's recent finding that changes in dipole moments of donor molecules by photo-excitation correlate with the short-circuit current (Carsten et al. in J Am Chem Soc 133(50): 20468, 2011). We found that the short-circuit current correlates with changes in dipole moments of complexes of donor and acceptor molecules rather than with the changes in dipole moments of donor molecules only. This is because of photoinduced partial charge transfer from the HOMO on the donor to the charge-bridging orbital that is delocalized over both donor and acceptor molecules. Therefore, we suggest that the change in the dipole moment in the complex of donor and acceptor molecules is a promising guideline for designing new donor molecules to improve the short-circuit current and PCEs.