Photoluminescence of P3HT:PCBM bulk heterojunction thin films and effect of external electric field

Abstract

AbstractSteady‐state and time‐resolved photoluminescence (PL) and electrophotoluminescence (E‐PL) have been recorded for bulk heterojunction samples of thin films of regio‐regular poly(3‐hexylthiophene) (P3HT) and methyl [6,6]‐phenyl‐C61‐butanoate (PCBM). The PL spectra of the bulk heterojunction samples showed a monotonic decrease of PL quantum yield with increased PCBM content in the film. The PL decay was measured with both a femtosecond up‐conversion technique and a time‐correlated single‐photon‐counting technique. The mechanism of PL quenching deviated from a simple Stern‐Volmer equation, explained in terms of an apparent static quenching with a sphere‐of‐action model and dynamic quenching. With increased content of PCBM, the static quenching played a dominant role. Upon application of an electric field, the E‐PL spectra of both P3HT and bulk heterojunction samples showed an enhanced quantum yield and incremented lifetime of PL of P3HT. The long‐range electron transfer from P3HT to PCBM was retarded upon application of an electric field; the field‐induced change increased with increasing PCBM content.