Molecular engineering of push-pull chromophore for efficient bulk-heterojunction morphology in solution processed small molecule organic photovoltaics
The synthesis and characterization of new push-pull chromophores, bisDMFA-diTh-CA, bisDMFA-diTh-MMN, and bisDMFA-diTh-MIMN from 5′-(4-(bis(9,9-dimethyl-9H-fluoren-2-yl)aniline (bisDMFA) electron donating, dithiophene bridging, and various electron withdrawing moieties, cyanoacrylic acid (CA), methylene malononitrile (MMN), and methylene indenylidene malononitrile (MIMN), were demonstrated for efficient solution processed BHJ solar cells. The photophysical properties, the hole mobilities from the space charge limitation of current (SCLC) J-V characteristics, and surface morphologies of these materials/PCBM bulk-heterojunction films were also investigated. The best power conversion efficiency of 3.66% (±0.12) with Jsc = 11.82 mA/cm2, FF = 0.35, and Voc = 0.90 V was observed in the BHJ film fabricated with the bisDMFA-diTh-MMN/C71-PCBM composite with 3% 1-chloronaphthalene (CN), which is an efficiency ∼82% and ∼49% higher than before and after post-annealing without treatment of CN, respectively.