Nonfullerene-Acceptor All-Small-Molecule Organic Solar Cells Based on Highly Twisted Perylene Bisimide with an Efficiency of over 6%

Two twisted singly linked perylene bisimide (PBI) dimers with chalcogen bridges in the PBI cores, named C4,4-SdiPBI-S and C4,4-SdiPBI-Se, were synthesized as acceptors for nonfullerene all-small-molecule organic solar cells (NF all-SMSCs). A moderate-band-gap small-molecule DR3TBDTT used as the electron donor displayed complementary absorption with C4,4-SdiPBI-S and C4,4-SdiPBI-Se. It was found that solvent-vapor annealing (SVA) played a critical role in the photovoltaic performance in NF all-SMSCs, which improves the crystallinity of the donor and acceptors, promotes the proper phase segregation domain size, and therefore enhances charge transport. The power conversion efficiencies (PCEs) of NF all-SMSC devices based on DR3TBDTT/C4,4-SdiPBI-S and DR3TBDTT/C4,4-SdiPBI-Se increased from 2.52% to 5.81% (J(SC) = 11.12 mA cm(-2), V-OC = 0.91 V, and FF = 57.32%) and from 2.65% to 6.22% (J(SC) = 11.55 mA cm(-2), V-OC = 0.92 V, and FF = 58.72%), respectively, after exposure to chloroform vapor. The best efficiency of 6.22% is one of the highest PCEs for NF all-SMSC-based PBI acceptors so far. The studies illustrate that highly efficient NF all-SMSCs can be achieved by using a PBI acceptor with a suitable SVA process.