A Donor-Acceptor Polymer with a Peculiar Negative-Charge-"Trapping" Characteristic

Voltammetric and spectrophotometric measurements of poly(3,3″‐dipentoxy‐3′‐dicyanoethenyl‐2,2′:5′,2″‐terthiophene) (polyCN) films, in connection with other experimental evidence, reveal a normal oxidative, but a peculiar reductive behavior consisting of trapping of the negative charge during the cathodic scan. Another interesting property of polyCN films is the tendency to form strong intramolecular and intermolecular associations, probably charge‐transfer (CT) complexes. These properties could account for the fact that the photovoltaic performance does not improve when polyCN is blended with a polythiophene donor. Normal oxidative behaviour but an unusual reductive behavior is shown in films of poly(3,3″‐dipentoxy‐3′‐dicyanoethenyl‐2,2′:5′, 2″‐terthiophene): the “trapping” of the negative charge during the cathodic scan. The tendency of this polymer to trap charges (see Figure) was probably the reason for the failure when using it as an acceptor in donor–acceptor blends for photovoltaics.