A novel carbazole–phenothiazine dyad small molecule as a non-fullerene electron acceptor for polymer bulk heterojunction solar cells

Abstract

A new organic small molecule, 2-((10-(6-(3,6-di-tert-butyl-9H-carbazole-9-yl)hexyl)-10H-phenothiazine-7-yl)methylene) malononitrile named CSORG5 has been synthesized and successfully applied for organic bulk heterojunction (BHJ) solar cells as a novel electron acceptor along with P3HT as a donor. The CSORG5 molecule possess facile synthesis, solution processability, visible light absorption, a properly matched lowest unoccupied molecular orbital (LUMO) energy level with conjugated polymers and moderate electron mobility, making the molecule an ideal acceptor for P3HT and other low band gap conjugated polymers. The BHJ organic solar cell constructed from a P3HT : CSORG5 (1 : 1) active layer processed from a DIO/THF solvent, exhibits a high open circuit voltage of up to 0.98 V resulting in an overall power conversion efficiency of 2.80%. Furthermore, the PCE is enhanced up to 4.16% when a thin layer of TiO₂ is inserted between the active layer and the Al electrode.