Low-Cost Silicon Phthalocyanine as a Non-Fullerene Acceptor for Flexible Large Area Organic Photovoltaics

We demonstrate large-area (1 cm²) organic photovoltaic (OPVs) devices based on bis(tri-n-butylsilyl oxide) silicon phthalocyanine (3BS)₂-SiPc as a non-fullerene acceptor (NFA) with low synthetic complexity paired with poly(3-hexylthiophene) (P3HT) as a donor polymer. Environment-friendly nonhalogenated solvents were used to process large area OPVs on flexible indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrates. An alternate sequentially (Alt-Sq) blade-coated active layer with bulk heterojunction-like morphology is obtained when using (3BS)₂-SiPc processing with o-xylene/1,3,5-trimethylbenzene solvents. The sequential (Sq) active layer is prepared by first blade-coating (3BS)₂-SiPc solution followed by P3HT coated on the top without any post-treatment. The conventional sequentially (Sq) blade-coated active layer presents very low performance due to the (3BS)₂-SiPc bottom layer being partially washed off by processing the top layer of P3HT. In contrast, alternate sequentially (Alt-Sq) blade-coated layer-by-layer film shows even better device performance compared to the bulk heterojunction (BHJ) active layer. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) and atomic force microscopy (AFM) reveal that the Alt-Sq processing of the active layer leads to a BHJ-like morphology with a well-intermixed donor-acceptor component in the active layer while providing a simpler processing approach to low-cost and large-scale OPV production.