Synergistic effect of side-chain engineering and terminal-group halogenation on naphthalenediimide-based non-fused ring electron acceptors for efficient organic solar cells

Abstract

Organic solar cells (OSCs) based on non-fused ring electron acceptors (NFREAs) have shown significant potential for practical application owing to their easily tunable chemical structures and short synthesis routes. The merging of side-chain engineering and terminal-group halogenation has facilitated the optimization of NFREAs properties. Thus, in this study, we developed four NFREAs using a naphthalenediimide (NDI) unit with different alkyl side-chains (–C₆C₁₀ or –C₈C₁₂) as the building block and two different electron-withdrawing groups 2-(3-oxo-2,3-dihydro-1H-inden-1-ylidene) malononitrile (IC) and chlorinated IC (IC-2Cl) as the terminal groups. These NFREAs were designated as NDI610-H, NDI610-Cl, NDI812-H, and NDI812-Cl, respectively. All four NFREAs exhibited similar optical bandgaps and molecular conformations. Under the synergistic effects of side-chain modification and terminal-group halogenation, the NFREAs-based active-layer morphologies were significantly different. The NDI610-Cl-based blended film demonstrated favorable phase-separation morphology, facilitating exciton dissociation and charge transport in the corresponding OSCs. Thus, the PM6:NDI610-Cl-based OSCs achieved a maximum power conversion efficiency (PCE) of 8.35%. Moreover, using D18 as the polymer donor further enhanced the device performance, with the D18:NDI610-Cl-based device yielding a higher PCE of 10.25% due to improved short-circuit current and fill factor. Our findings indicate that selecting an NDI unit as the building block and combining tailored alkyl side-chains with altered terminal groups are promising strategies for constructing highly efficient NFREAs.