Novel A-π-A-D type perylene diimide acceptor for high-performance fullerene-free organic solar cells

Abstract

Two novel PDI-based acceptors PDI-SPAc and FPDI-SPAc, which contain perylene diimide (PDI) and a quasi-two-dimensional (quasi-2D) fused PDI (FPDI), respectively, with electron-rich unit 10 H-spiro[acridan-9,9′-fluorene] (SPAc), were designed and synthesized to investigate their application in non-fullerene organic solar cells (NF-OSCs). Expectedly, FPDI-SPAc obtained a fairly twisted conformation in consequence of the quasi-2D configuration of FPDI unit and significant dihedral angle between FPDI and SPAc units. Geometry of PDI-SPAc containing only dihedral angle between PDI and SPAc units was confirmed, too. The optical properties, electron energy levels, charge transport properties, photovoltaic performance, charge dissociation probabilities, and surface morphology were systematically investigated subsequently. By blending with a narrow band-gap polymer PTB7-Th as the polymer donor, NF-OSC based on PTB7-Th:FPDI-SPAc achieved a power conversion efficiency (PCE) of 3.92% with the dominant configuration characteristic, whereas the PDI-SPAc-based NF-OSC exhibited a PCE of only 0.32% with a significantly reduced short-circuit current density (Jsc) of 1.2 mA/cm2. The interesting results indicate that, the quasi-2D structure of FPDI unit produced impressive effect on the photovoltaic performances of the FPDI derivative acceptors, which can demonstrate that quasi-2D structure is a better electron-deficient segment in comparison with PDI for the design of n-type photovoltaic materials.