Cracking perylene diimide backbone for fullerene-free polymer solar cells

Through cracking perylene diimide by inserting a single bond, small pi-conjugation unit thiophene and large ir-conjugation unit indaceno[1,2-b:5,6-b']dithiophene, three molecules were synthesized and used as electron acceptors for solution-processed polymer solar cells. These three compounds showed excellent thermal stability with decomposition temperatures over 370 degrees C. As the size of inserted conjugation units increased, the extinction coefficient increased from 2.9 x 10(4) to 6.5 x 10(4) M-1 cm(-1), the absorption wavelength maximum in thin film red shifted from 360 to 488 nm, the optical band gap decreased from 2.98 to 2.25 eV, the highest occupied molecular orbital energy level was upshifted from -6.18 to -5.67 eV, the lowest unoccupied molecular orbital energy level was downshifted from -3.59 to -3.68 eV, power conversion efficiencies of solar cells based on blends of poly(3-hexylthiophene) donor and these acceptors increased from 0.28% to 2.36%. (C) 2016 Elsevier Ltd. All rights reserved.