Energy Alignment of Frontier Orbitals and Suppression of Charge Recombinations in P3HT/SWNT

Blends of poly(3-hexylthiophene) (P3HT) and single-walled carbon nanotubes (SWNTs) have been studied as promising materials for organic photovoltaic devices because of the excellent electronic properties of SWNT and a broad interfacial area guaranteed by the helical structure of P3HT at the interface. However, the P3HT/SWNT blends show a low energy conversion efficiency, and thus, a deeper understanding of the charge separation process in the P3HT/SWNT blends is required to achieve improved efficiency. In this paper, the electronic structures of P3HT at the interface and in the bulk phase were studied to elucidate the charge separation process in the P3HT/SWNT blends. We show the existence and origin of the difference between the HOMO levels at the interface and those in the bulk phase. This explains observations in a previous experiment where long-lived charge carriers were only observed in blends containing excess P3HT. In the course of the investigation on the electronic structures, the role of the sid...