Defective conjugated polymers for organic electronics

This contribution discusses recent progress in the area of the synthesis of conjugated polymers for organic electronics. A first focus is on the role of chemical defects that form during synthesis. Depending on monomer structure, synthetic method and reaction conditions, homocouplings form at varying extent in donor-acceptor copolymers. This deviation from the usually suggested, strictly alternating structure lowers performance and causes a low level of reproducibility. In PCDTBT, homocouplings lower the short circuit current of photovoltaic devices and may be considered as one source for the broad range of reported power conversion efficiencies. The second part includes n-type copolymers from the naphthalene diimide and diketopyrrolopyrrole families. Defect formation, molecular weight control and energy level tuning is elucidated and correlated with charge carrier mobility and photovoltaic performance. A central conclusion is that the general understanding of the occurrence and importance of chemical defects in conjugated polymers has improved, but their entire elimination remains to be solved rendering batch to batch reproducibility a challenge.