Effect of linear side-chain length on the photovoltaic performance of benzodithiophene-alt-dicarboxylic ester terthiophene polymers

Abstract

Conjugated polymers (P3TE-C8 and P3TE-C12) with two different side chains based on thienyl-substituted benzodithiophene and dicarboxylic ester terthiophene were synthesized and applied in non-fullerene polymer solar cells (PSCs). Detailed studies revealed that the length of side chains in conjugated polymers showed a weak influence on their optical bandgaps and electrochemical properties, but a strong influence on their aggregation behaviors in solution, films, bulk heterojunction morphologies and photovoltaic performances. Among PSC devices, the P3TE-C8:ITIC-based device showed a PCE of 5.49%, a V_OC of 0.814 V, J_SC of 12.86 mA cm⁻² and FF of 52.48%, while the P3TE-C12:ITIC-based device exhibited a higher PCE of 7.64%, with simultaneously improved photovoltaic parameters of V_OC of 0.906 V, J_SC of 14.20 mA cm⁻² and FF of 59.36%. This work demonstrates that the reduction aggregation in conjugated polymers via changing the length of side chains is an effective method to improve PSC performances.