Effect of ZnO ETL and MoO3 HTL with PCDTBT:PC70BM-based BHJ organic solar cells

Abstract

In this work, the authors fabricated and characterized efficient inverted organic solar cells by modifying them with a highly transparent sol–gel-derived zinc oxide (ZnO) film as an electron transport layer and optimized molybdenum trioxide (MoO3) as a hole transport layer with a very low-bandgap polymer, poly[N-900-hepta-decanyl-2,7-carbazole-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)] (PCDTBT), in bulk heterojunction (BHJ) composites with the fullerene derivative [6,6]-phenyl-C70-butyric acid methyl ester (PC70BM) BHJ in various solvents. Variations in the sol concentration, thickness, surface and optical characteristics of inverted organic solar cell glass/indium tin oxide/zinc oxide/PCDTBT:PC70BM/molybdenum trioxide/silver (Ag) structures were investigated and analyzed. The thickness of zinc oxide increased as the sol concentration increased from 10 to 100 nm. With the modification of the PCDTBT:PC70BM solvent, the device efficiency improved from 4.22 to 7.43%, which was accompanied by an improvement in the open-circuit voltage (V oc) from 0.87 to 1.03 V and enhancement of the short-circuit current density (J sc) from 9.1 to 13.5 mA/cm2.