Transient extraction of holes and electrons separately unveils the transport dynamics in organic photovoltaics

We have utilized the metal–insulator–semiconductor charge extraction by linearly increasing voltage (MIS-CELIV) technique to clarify the hole- and electron-transport properties in benchmark poly(3-hexylthiophene) (P3HT) and its blend with phenyl-C61-butyric acid methyl ester (PCBM) by using a thick lithium fluoride (LiF) as the charge-blocking layer. Both dark and light MIS-CELIV are employed to comparatively investigate the differences in the recombination process and charge mobilities in neat P3HT and P3HT:PCBM blends. Our studies quantitatively show that balanced hole and electron transport can be achieved in the P3HT:PCBM blend under light illumination, leading to a high efficiency in the photovoltaic cell. Furthermore, light MIS-CELIV can be employed as a novel method to directly evaluate the capability of photoelectric conversion of organic photovoltaic materials.