Effect of Organic Solar Cell Using Double Cathode Buffer Layers

The effect of small molecule organic solar cell based on Boron Subphthalocyanine Chloride (SubPc) and fullerene (C₆₀) by using the double cathode buffer layers was studied. The structure of device is indium tin oxide (ITO)/SubPc (9 nm)/C₆₀ (30 nm)/ 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (10 nm)/3,4,910-perylenetetracarboxylic bis-benzimidazole (PTCBI) (0~3 nm)/aluminum (Al). The thickness of PTCBI in device is varied from 1 nm to 3 nm to get the optimal thickness for the better performance. The power conversion efficiency of device was improved from 2.317% to 2.558% by inserting PTCBI of 1 nm between BCP and Al. The enhancement of efficiency is attributed to the shunt resistant of device increasing from 634 Ω-cm² to 784 Ω-cm², resulting in an iprovement of the short current density and the fill factor. From the measurement of external quantum efficiency, it can be found that the percentage of light converted into electrons is increased in whole absorption wavelength of device, showing that the function of PTCBI is not as the optical spacer layer. As a result, the PTCBI is served as an electron transport layer which can export the carrier easily and reduce the carrier recombination.