Novel indacene-1,3,5,7-tetraone-based polymerized small molecular acceptors for efficient all-polymer solar cells

Abstract

Polymerized small molecular acceptors (PSMAs) as polymer acceptors demonstrate great potential in fabricating high-performance all-polymer solar cells (all-PSCs), but the available type of electron-deficient end-capping groups for polymerizable non-fullerene small molecular acceptors (NFSMAs) block is still few, limited by the commonly-used Stille polymerization method. Herein, we demonstrated novel PSMAs with an indacene-1,3,5,7-tetraone (ITO) motif as end-capping groups, namely PBDT-ITO and PBDTCl-ITO, and their application as acceptors for efficient all-PSCs. It was found that an electron-deficient ITO motif provides the relevant polymer with a stronger pull-push effect and larger conjugation length, resulting in lower-lying LUMO energy levels and decent electron mobility. After combining them with a classical polymer donor PM6 to fabricate binary all-PSCs, the PBDTCl-ITO-based device can deliver the best efficiency of 7.55% and a remarkable open-circuit voltage (V_OC) over 1 V. Relative to the PBDT-ITO-based counterpart, efficient hole/electron transfer, relatively higher and balanced charge transport property and proper morphology should be responsible for a better device performance. Furthermore, owing to the proper energy levels, complementary absorption and improved charge separation/transport, incorporating PBDTCl-ITO into an efficient PM6:PY-IT active layer can also promote V_OC and short-circuit current density (J_SC), thus leading to a ternary all-PSC with 16.08% efficiency. This work enriches the family of end-capping groups for designing efficient PSMAs, and further investigation on molecular backbone design, such as selection of core units and π-bridge units, would stimulate better all-PSC devices.