Underlying effects of diiodooctane as additive on the performance of bulk heterojunction organic solar cells based small organic molecule of isatin-core moiety

This paper reports the synthesis of D-A type π-conjugated organic chromophore, 1-hexyl-5-(5′-hexyl-[2,2′-bithiophen]-5-yl)indoline-2,3-dione (RBTh-NR) using isatin-core moiety as strong electron-acceptor and terminal alkyl bithiophene as electron-donor. The synthesized RBTh-NR chromophore was utilized as donor material for the fabrication of the solution processed bulk heterojunction organic solar cells (BHJ-SMOSCs) and the effects of 1,8-diiodooctane (DIO) as an additive was investigated. Due to the presence of isatin-core moiety, RBTh-NR displayed good optical properties with absorption at ∼526 nm. The obtained cyclicvoltametry (CV) results exhibited good HOMO and LUMO energy levels of −5.24 eV and −3.46 eV, respectively for RBTh-NR thin film. The use of DIO as an additive in an active layer considerably improved the morphology, and also tuned the optical and electrical properties. As compared to the pristine device, the performance of RBTh-NR-PC₆₁BM-DIO (1:3, w/w) active layer based optimized BHJ-SMOSC displayed the better performance with enhanced power conversion efficiency (PCE) of ∼4.10 %, short circuit current density (Jsc) of ∼12.21 mA/cm² and improved fill factor (FF) of ∼45%.