Fullerene derivatives (e.g., PC₆₁BM/PC₇₁BM) are widely used acceptors in organic solar cells (OSCs). However, their obvious drawbacks, such as limited chemical and energetic tunabilities, poor light absorption, high production cost and morphological instability, have become the bottlenecks to constrain the further advancement of OSCs. In this work, 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 shows energy levels matching perfectly with those of the commonly used poly(3-hexyl thiophene) (P3HT) donor in polymer solar cells (PSCs). Furthermore, SF(DPPB)₄ shows a cross-shaped molecular geometry, which helps suppressing the strong intermolecular aggregation in P3HT:SF(DPPB)₄ blend. PSCs based on P3HT:SF(DPPB)₄ blend exhibit the best PCE of 5.16% with a V_oc of 1.14 V. To the best of our knowledge, this efficiency is one of the highest values reported in literatures to date for P3HT based fullerene-free PSCs. 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 than the P3HT:PC₆₁BM ones. The above results demonstrate that new design strategy to access high-performance non-fullerene acceptor, SF(DPPB)₄, is promising for the future practical application of PSCs.

The article was published on Energy & Environmental Science.

 

 

Shuixing Li,‡ Wenqing Liu,‡ Minmin Shi,* Jiangquan Mai, Tsz-Ki Lau, Junhua Wan, Xinhui Lu, Chang-Zhi Li* and Hongzheng Chen*, Energy Environ. Sci., 2015, DOI: 10.1039/C5EE03481G.