Naphthalene diimide-based small molecule acceptors for organic solar cells

摘要: This work introduces six novel naphthalene diimide (NDI) molecular acceptors for evaluation in organic solar cells based on two different chemical architectures: a star-shaped structure with triarylamine core flanked by three NDI moieties and linear molecule composed of bithiophene bridge between moieties. For each structure, side chains are examined, alkyl linked to the either through oxygen, sulfur, or nitrogen substituents. Both side-chain heteroatom substitution were found influence optoelectronic photovoltaic properties these acceptors. Organic fabricated acceptor, utilizing PBDTTT-EFT (also known as PTB7-Th) donor material inverted bulk-heterojunction devices. Nitrogen was observed lower cell performance significantly decreasing short circuit current density (JSC), while sulfur increased JSC and, star configuration, led highest power conversion efficiency (PCE) 2.8% – which is amongst any NDI-based acceptor date. Grazing incidence wide-angle X-ray scattering (GIWAXS) measurements materials showed substitutional atom alters material's packing configuration neat films, films blended showing features characteristic materials, indicating that small molecules do not disrupt (and vice versa). Resonant soft (R-SoXS) indicate PBDTTT-EFT:star-shaped blends subject coarse phase-separation, average domain size all typically being less than 100 nm. confirmed similar topography AFM images Photoluminescence (PL) quenching measurements, however, large differences PL attributed driving force charge transfer, substituted compound lowest replacement highest.