A spirobifluorene and diketopyrrolopyrrole moieties based non-fullerene acceptor for efficient and thermally stable polymer solar cells with high open-circuit voltage

In this study, we design and synthesize a new non-fullerene electron acceptor, SF(DPPB)(4), in which a spirobifluorene (SF) core is installed with four benzene endcapped diketopyrrolopyrrole (DPP) arms. SF(DPPB)(4) exhibits energy levels matching perfectly with those of the commonly used poly(3-hexyl thiophene) (P3HT) donor in polymer solar cells (PSCs). Furthermore, a designed cross-shaped molecular geometry helps in suppressing strong intermolecular aggregation in the P3HT:SF(DPPB)(4) blend, leading to efficient non-fullerene PSCs. The resultant devices give a maximum power conversion efficiency (PCE) of 5.16% with an extremely high open-circuit voltage (V-oc) of 1.14 V. In contrast, the devices based on P3HT:PC61BM blends provide a PCE of 3.18% with a V-oc of 0.62 V. Finally, we observe that the P3HT:SF(DPPB)(4) devices exhibit significantly improved thermal stability from that of the P3HT:PC61BM devices; upon thermal treatment at 150 degrees C for 3 h, the PCEs of P3HT:SF(DPPB)(4) devices remain unchanged, whereas those of the P3HT:PC61BM devices drop drastically to below 1%. The abovementioned results demonstrate that the new design strategy of employing a high-performance non-fullerene acceptor, SF(DPPB)(4), is promising for the future practical application of PSCs.