Vacuum-Deposited Organic Solar Cells Based on a Dicyanovinyl-Terminated Small-Molecule Donor

Abstract

The design and synthesis of photoactive semiconducting materials with an appropriate band gap and charge transport properties are crucial for developing vacuum-deposited organic solar cells (VD-OSCs). In this work, we synthesized a novel conjugated material, 2,2′-(((4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl)bis([2,2'-bithiophene]-5′,5-diyl))bis(methanylylidene))dimalononitrile (BBTBDTM), with a symmetric A-π-D-π-A architecture. BBTBDTM contains benzodithiophene as the central donor (D), bithiophene as the conjugated spacer (π), and dicyanovinyl as the acceptor (A). This effective “push-pull” structure gives rise to a bandgap of 1.5 eV and leads to the favorable energy level alignment with the C60 acceptor that is suitable for solar flux absorption and charge transport in VD-OSCs. Notably, the insertion of the co-deposited BBTBDTM:C60 layer between the BBTBDTM and C60 layers improved the interfacial contact between BBTBDTM and C60. As a result, the power conversion efficiency of the BBTBDTM:C60-based VDOSCs reaches 1.49% (VOC of 0.70 V, JSC of 4.56 mA cm-2 and FF of 0.47) under AM 1.5 illumination.