Tailoring non-fullerene acceptors to enhance molecular ordering in inverted bilayer organic solar cells

Abstract

Breakthroughs in non-fullerene acceptors (NFAs) have propelled organic solar cells (OSCs) to new efficiency heights. However, most OSCs expose NFAs at the active-layer surface, reducing storage stability. Herein, we fabricated inverted bilayer OSCs comprising the polymer donor PM6 and various NFAs via the transfer-printing method to elucidate the impact of NFA morphology on device performance. The results show that when NFA BTP-eC9 is used as the acceptor, a denser film with a smoother surface is formed, which prolongs the carrier lifetime and enhances the charge-extraction efficiency, leading to superior device performance. Furthermore, the ultra-dense film forms an impenetrable shield that bars PM6 intrusion and immobilizes the morphology, securing rock-steady device stability. The findings elucidate that optimizing the morphology of NFAs can enhance the efficiency of inverted bilayer OSCs, which is a practical approach to achieving stable OSCs.