ABSTRACT
A series of self-assembled monolayer (SAM)-based benzoic acid derivatives such as 4-[5'-phenyl-2,2'-bitien-5-yl] benzoic acid (ZE-Ph), 4-[5'-(4-fluorophenyl)-2,2'-bitien-5-yl]benzoic acid (ZE-1F), and 4-[5'-(3,5-difluorophenyl)-2,2'-bitien-5-yl]benzoic acid (ZE-2F) were synthesized to use an interlayer between an ITO electrode and a MoO3 thin film layer in an organic solar cell (OSC) having poly-3 hexylthiophene (P3HT): [6,6]-phenyl C61 butyric acid methyl ester (PC61BM) blend. The work function and surface wetting properties of the ITO were tuned by SAM molecules. The power conversion efficiency of fabricated OSC devices was improved compared to that of the control device from 1.93 to 2.20% and 2.22% with ZE-Ph and ZE-1F-modified ITO electrodes, respectively. The short-circuit current density (Jsc) was increased from 6.16 to 7.10 mA/cm2 and 6.94 mA/cm2 with control, ZE-Ph, and ZE-1F-modified solar cells, respectively. The increase in short-circuit current density (Jsc) shows that the hole-transporting properties between ITO and MoO3 were improved by the use of ZE-Ph and ZE-1F compared with that of the ITO/MoO3 electrode configuration. The open-circuit voltage (Voc) of the SAM-modified ITO-based devices was also improved compared with the Voc of unmodified ITO-based devices. These results show that using a monolayer as an interlayer in OSCs is an important strategy to improve the performance of OSCs. All the device parameters were characterized by Kelvin probe force microscopy, cyclic voltammetry, contact angle, and I-V measurements.
