Facile Synthesis of Polycyclic Aromatic Hydrocarbon (PAH)-Based Acceptors with Fine-Tuned Optoelectronic Properties: Toward Efficient Additive-Free Nonfullerene Organic Solar Cells

Abstract

A series of polycyclic aromatic hydrocarbons (PAHs) with extended pi-conjugated cores (from naphthalene, anthracene, pyrene, to perylene) are incorporated into nonfullerene acceptors for the first time. Four different fused-ring electron acceptors (FREAs), i.e., DTN-IC-2Ph, DTA-IC-3Ph, DTP-IC-4Ph, and DTPy-IC-5Ph, are prepared via simple and facile synthetic procedures, yielding a remarkable platform to study the structure-property relationship for nonfullerene solar cells. With the PAH core being extended systematically, the gradually redshifted absorption with enhanced molar extinction coefficient (epsilon) is realized, the energy level of the highest occupied molecular orbital is up-shifted, and the electron mobility is greatly enhanced. Meanwhile, the solubility decreases and the molecular packing becomes strengthened. As a result, with an optimized combination of these characteristics, DTP-IC-4Ph attains good solubility, high molar extinction coefficient, complementary absorption, suitable morphology, well-matched energy levels, as well as efficient charge dissociation and transport in blend film. Consequently, the DTP-IC-4Ph-based solar cells with a donor polymer, poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b ']dithiophene))-alt-(5,5-(1 ',3 '-di-2-thienyl-5 ',7 '-bis(2-ethylhexyl)benzo[1 ',2 '-c:4 ',5 '-c ']dithiophene-4,8-dione))] (PBDB-T) exhibit a promising power conversion efficiency of 10.37% without any additives, which is close to the best performance achieved in additive-free nonfullerene solar cells (NFSCs). The results demonstrate that the PAH building blocks have great potential for the construction of novel FREAs for efficient additive-free NFSCs.