Unlocking the potential of diketopyrrolopyrrole-based solar cells by a pre-solvent annealing method in all-solution processing

Abstract

In this work, we report a solution processible diketopyrrolopyrrole anthracene based diblock copolymer synthesized via a rapid direct C–H arylation coupling method. After optimizing the combination of solvent and thermol annealing process, we investigated the characteristics of this di-block low band gap copolymer used as a donor part in bulk hetero-junction solar cells. The influence of the polymer:fullerene ratio (PDPP-ANT:PC₆₁BM) and annealing conditions on the photo active film nanomorphology and device performance has been studied in detail. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveal that the resulting film morphology strongly depends on the fullerene ratio before heat treatment. Power conversion efficiencies increase, more than four-fold, to 1.7% for regular architectures with high V_oc (0.73 V), J_sc (4.75 mA cm⁻²) and FF (49.0%), compared with the unannealed device 0.37% (with V_oc (0.54 V), J_sc (1.83 mA cm⁻²), FF (37.8%)). Furthermore, the two broad absorption bands of the PDPP-ANT materials show their potential to be applied in ternary polymer solar cells and tandem polymer solar cells.