Isoindigo has been extensively used to synthesize electron donor materials for organic photovoltaics; however, there are only a few non-fullerene electron acceptors made of the isoindigo core. Poly(isoindigo) was the first isoindigo-based non-fullerene acceptor. It exhibited an extremely low electron mobility and poor photovoltaic performance in all-polymer solar cells. The poor electron mobility was due to a lack of planarity in the polymer backbone, which was caused by the torsional angle between adjacent isoindigo units. This distortion can be avoided by introducing a sterically unencumbered spacer between two neighboring monomer units. In this poster, the synthesis of poly(ethynylisoindigo) is presented, where the ethynyl group helps reduce torsion and conserve planarity in the polymer backbone. The poster focuses on the effect of the spacer on the frontier molecular orbitals, electron mobility and photovoltaic performance of the copolymer.