Enhanced photoluminescence at poly(3-octyl-thiophene)/TiO2 interfaces

The photoluminescence (PL) of poly(3-octyl-thiophene) (P3OT) thin films applied on TiO2 substrates is compared to the PL of P3OT films applied on quartz. Quenching of excitons occurs at the P3OT/TiO2 interface and not at the P3OT/quartz interface. Yet, in the former case the PL intensity is stronger than in the latter. In particular, P3OT films less than 5 nm thick lumines much more when applied on TiO2, which is in striking contrast to what one expects. For films thicker than 10 nm, the increase of the PL as function of the film thickness is the same for TiO2 and for quartz, which indicates that the PL enhancement originates at the interface. The dissociation of excitons at the P3OT/TiO2 interface yields positive polarons in P3OT, which is not the case at the P3OT/quartz interface. We postulate that interaction between positive polarons and excitons explain the observed enhancement of the PL at the P3OT/TiO2 interface. (C) 2004 American Institute of Physics.