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

Abstract

Although a bulk heterojunction (BHJ) structure enables high power conversion efficiencies (PCEs) in organic solar cells (OSCs), the morphology of the donor:acceptor blend film is thermally unstable due to molecular diffusion of the two components, especially the small-molecule acceptor (SMA). Herein, distinct from the widely applied oligomerization or polymerization of SMAs, we reported a new and simple strategy involving the substitution of adamantyl, the rigid alkyl group, on the well-known SMA of Y6-BO to improve the thermal stability of OSCs. Through such molecular tailoring, two novel SMAs, BOAD and ADAD, which possessed one and two adamantyl side chains, respectively, were synthesized. As expected, the glass transition temperatures (T_gs) of ADAD and BOAD were elevated from 78 °C for Y6-BO to 98 °C and 123 °C, respectively. Consequently, after thermal treatment at 80 °C for 375 h, the BOAD-based OSC retained 61.3% of its initial efficiency, outperforming its Y6-BO-based counterpart (44.9%). In addition, the BOAD-based device achieved a high PCE of 17.13%, comparable to that of the Y6-BO-based device (16.98%). Our work provides a valuable reference for designing stable SMAs, advancing the commercialization of OSCs.