Simultaneous determination of electron and hole drift mobilities in working inverted organic solar cells: modulated photocurrent spectroscopy versus impedance spectroscopy

Applicability of modulated photocurrent (MPC) spectroscopy and impedance spectroscopy (IS) were examined both experimentally and numerically to simultaneous determination of electron and hole drift mobilities in working prototypical inverted organic photovoltaics (OPVs) of poly(3-hexylthiophene) (P3HT):1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM) bulk heterojunction (BHJ). Charge carriers were photoinjected in MPC measurements and were injected from electrodes in IS. The P3HT:PCBM composition of the BHJ was chosen so as to observe both electron and hole transits separately. Electron and hole transits were simultaneously observed in the inverted OPVs by means of MPC measurements, while only hole transit was observed by means of IS. The device simulation shows that the reason that electron transit was not observed in the inverted OPVs by means of IS is due to the electron injection barrier of >0.2 eV inevitably existed in the inverted OPVs.