High-efficiency flexible organic solar cells with a polymer-incorporated pseudo-planar heterojunction

Organic solar cells (OSCs) are considered as a crucial energy source for flexible and wearable electronics. Pseudo-planar heterojunction (PPHJ) OSCs simplify the solution preparation and morphology control. However, non-halogenated solvent-printed PPHJ often have an undesirable vertical component distribution and insufficient donor/acceptor interfaces. Additionally, the inherent brittleness of non-fullerene small molecule acceptors (NFSMAs) in PPHJ leads to poor flexibility, and the NFSMAs solution shows inadequate viscosity during the printing of acceptor layer. Herein, we propose a novel approach termed polymer-incorporated pseudo-planar heterojunction (PiPPHJ), wherein a small amount of polymer donor is introduced into the NFSMAs layer. Our findings demonstrate that the incorporation of polymer increases the viscosity of acceptor solution, thereby improving the blade-coating processability and overall film quality. Simultaneously, this strategy effectively modulates the vertical component distribution, resulting in more donor/acceptor interfaces and an improved power conversion efficiency of 17.26%. Furthermore, PiPPHJ-based films exhibit superior tensile properties, with a crack onset strain of 12.0%, surpassing PPHJ-based films (9.6%). Consequently, large-area (1 cm2) flexible devices achieve a considerable efficiency of 13.30% and maintain excellent mechanical flexibility with 82% of the initial efficiency after 1000 bending cycles. These findings underscore the significant potential of PiPPHJ-based OSCs in flexible and wearable electronics.