A three-dimensional thiophene-annulated perylene bisimide as a fullerene-free acceptor for a high performance polymer solar cell with the highest PCE of 8.28% and a VOC over 1.0 VElectronic supplementary information (ESI) available: Synthesis, calculations, SCLC plots. See DOI: 10.1039/c7tc05261h

A new propeller-shaped small-molecule acceptor of BPT-S with S-annulated perylene bisimide (PBI) as peripheral groups was designed and synthesized. Compared to the unannulated counterpart ( BPT ), BPT-S exhibits a blue-shift absorption spectrum, stronger absorption in the region of 400-510 nm, higher LUMO energy level and twisted molecular geometry. The BPT-S -based device with PDBT-T1 as the donor achieved a power conversion efficiency (PCE) as high as 8.28% with an impressively high open-circuit voltage ( V OC ) of 1.02 V, a near 16% enhancement in PCE with respect to the BPT -based control device (7.16%). The high photovoltaic performance for the BPT-S -based device can be attributed to its relatively high-lying LUMO level, complementary absorption spectra with the donor material, favorable morphology and balanced carrier transport. To the best of our knowledge, a PCE of 8.28% is the highest value for the device based on S-annulated PBIs as acceptors reported so far. This work indicates the great potential of the 3D S-annulated PBI-based acceptors for tandem (or multi-junction) organic solar cells due to the proper absorption spectra and high photovoltaic performance. PSCs based on BPT-S achieved the PCE of 8.28%, which is the highest value based on S-annulated PBIs acceptors so far.