New quinoxaline and pyridopyrazine-based polymers for solution-processable photovoltaics

The recently published quinoxaline/thiophene-based polymer TQ1 has been modified on its acceptor unit, either altering the acceptor strength by incorporating a pyridopyrazine, substitution of the acceptor-hydrogens by fluorine, or substitution of the alkoxy side chain by alkyl. The changes in physical, electronic and device properties are discussed. For the polymers incorporating the stronger acceptors a decreased performance is found, where in both cases the current in the devices is compromised. Incorporation of the pyridopyrazine-based acceptor seems to result in more severe or additional loss mechanisms compared to the polymer that incorporates the fluorine atoms. A similar performing material is obtained when changing the alkoxy side chain in TQ1 to an alkyl, where the solar cell performance is mainly improved on the fill factor. It is demonstrated that the standard TQ1 structure is easily modified in a number of ways, showing the versatility and robustness of the standard TQ1 structure and synthesis.

► Three new TQ1 derivatives with modified acceptor structure have been synthesized.
► The synthesis of TQ1 is robust towards the changes done on the acceptor unit.
► Very different photovoltaic properties have been observed for the small alterations.
► Substituting the alkoxy side chains for alkyl improves some of the PV properties.