Chemical modification of small molecule acceptor with adamantyl side chain for efficient and thermally stable organic solar cells

Abstract

Although bulk heterojunction (BHJ) structure ensures high power conversion efficiencies (PCEs) of organic solar cells (OSCs), the morphology of this donor:acceptor blend film is thermally unstable due to molecular diffusion of two components, especially small molecule acceptor (SMA). Herein, different from the widely applied oligomerization or polymerization of SMAs, we report a new and simple strategy of the substitution with adamantyl, the most rigid alkyl group, on a famous SMA of Y6-BO to improve thermal stability of OSCs. Through such molecular tailoring, two novel SMAs of BOAD and ADAD, which owns one and two adamantyl side chains, respectively, are synthesized. As expected, the glass transition temperatures of ADAD and BOAD are elevated from 78 oC of Y6-BO to 98 ℃ and 123 ℃, respectively. Thus, after thermal treatment at 80 ℃ for 375 hours, the BOAD-based OSC maintains 61.3% of its initial efficiency, outperforming the Y6-BO-based counterpart (44.9%). In addition, the BOAD-based device achieves a high PCE of 17.13%, which is comparable to the Y6-BO-based one (16.98%). Our work provides a valuable reference to design stable SMAs, advancing the commercialization of OSCs.