Effect of temperature on carrier formation efficiency in organic photovoltaic cells

The internal quantum efficiency (ϕIQ) of an organic photovoltaic cell is governed by plural processes. Here, we propose that ϕIQ can be experimentally decomposed into carrier formation (ϕCF) and carrier transfer (ϕCT) efficiencies. By combining femtosecond time-resolved and electrochemical spectroscopy, we clarified the effect of temperature on ϕCF in a regioregular poly(3-hexylthiophene) (rr-P3HT)/[6,6]-phenyl C61-butyric acid methyl ester blend film. We found that ϕCF (=0.55) at 80 K is the same as that (=0.55) at 300 K. The temperature insensitivity of ϕCF indicates that the electron-hole pairs at the D/A interface are seldom subjected to coulombic binding energy.