dc and transient photoconductivity of poly(2-phenyl-1,4-phenylenevinylene)

Abstract

Generation and transport of charge carriers in poly(2-phenyl-1,4-phenylenevinylene) has been investigated by means of dc and transient photoconductivity. Photocarrier production is temperature and field assisted and is appropriately described within the framework of the one-dimensional Onsager theory of geminate-pair dissociation. The geminate pairs are formed by disorder-assisted dissociation of primarily excited localized singlet excitations of chain segments. At high fields the geminate-pair yield is of order unity. Time-of-flight signals are characteristic of a disordered solid. After an initial dispersive decay, a plateau is attained, followed by a long-lasting tail. Hole mobilities decrease with increasing electric field---suggestive of the importance of off-diagonal disorder---and carry a temperature dependence characteristic of hopping within a Gaussian density of states 90 meV in width. No evidence for polaronic effects is found.