Side chain effect on photovoltaic properties of dibenzo[a,c]phenazine based donor–acceptor polymers

• The PSCs properties of BPz derivatives based donor polymers can be affected by the different side chain substitutions.
• The HOMO of PBDT-BPzC with 2,7-alkyl substituted is significantly lower than PBDT-OBPz with 11,12-alkoxy substituted.
• PBDT-BPzC significantly enhances the Voc and PCE, compared with PBDT-OBPz.

The electron–donor polymers containing dibenzo[a,c]phenazine (BPz) derivatives with 2,7-alkyl and 11,12-alkoxy substituted, PBDT-BPzC and PBDT-OBPz, respectively, were synthesized to investigate the photovoltaic effect of different side chain substitutions. The polymers exhibit similar physical properties, except the HOMO and LUMO of PBDT-BPzC are 0.18 and 0.15 eV deeper than PBDT-OBPz, resulting in the Voc of polymer solar cells (PSCs) based on PBDT-BPzC are above 0.1 V higher than that of PBDT-OBPz. With the contribution of the superior Voc, polymer PBDT-BPzC showed preferable photovoltaic performances, and the PCE reached 4.44%, which is 0.49% higher than PBDT-OBPz. This research reveals a preferred side chain substituted way to modify BPz unit, and gives an optimally developing the dibenzo[a,c]phenazine derivatives based electron–donor polymers.

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