Electrochemical and photovoltaic properties of electropolymerized poly(thienylsilole)s

Electrochemical and photoelectrochemical properties were studied of a series of donor-acceptor materials based on polythiophene modified with silole moieties. The materials were prepared by electrochemical anodic polymerization of 2,5-bis([2,2'-bithiophen]-5-yl)-1,1-dimethyl-3,4-diphenylsilole and 2,5-bis([2,2'-terthiophen]-5-yl)-1,1-dimethyl-3,4-diphenylsilole, as well as copolymerization of these monomers with 2,2'-bithiophene. Photocurrent measurements showed that introduction of silole resulted in a considerable enhancement of the photovoltaic properties of silole-containing materials and especially the fill factor. However, as demonstrated by Mott-Schottky measurements, electropolymerized silole-containing materials showed a substantial degree of disorder and high density of states in the midgap, which negatively affected their photovoltaic properties. Atomic force microscopy (AFM) and phase imaging revealed the presence of phase segregation and heterogeneity of the silole-containing materials. Interestingly, introduction of siloles suppressed the cathodic (n-type) doping typical for polythiophenes. This work demonstrates that siloles show great promise as electron-acceptor groups for all-organic solar cells; however, further work is required to optimize the properties and performance of poly(thienylsilole)-based materials.