Investigation into the Thermal Annealing Effect on the Photovoltaic Properties of Organic Solar Cells based on CuPc/C60 Heterojunctions

Abstract

We studied the effect of post-annealing treatment on the photovoltaic (PV) properties of or- ganic solar cells based on copper phthalocyanine (CuPc)/fullerene (C60) heterojunctions. In the device structure of ITO/CuPc (30 nm)/C60(40 nm)/BCP(10 nm)/LiF(0.5 nm)/Al, where BCP is 2,9-dimethyl-4,7-diphenyl-phenanthroline acting as an exciton blocking layer, a maximum power conversion effciency (np) of about 1 % under an AM 1.5 solar illumination intensity of 100 mW/cm2 was obtained at room temperature. By measuring the PV characteristics for the devices annealed at various temperatures for 30 minutes, we found that the short-circuit current and e ciency increased with increasing annealing temperature up to 100 C (np 1:3 %) and then decreased at higher temperatures. We analyzed the effect of thermal annealing on the improved device performance by measuring the optical absorption spectra and the X-ray diffraction patterns of the CuPc/C60 films.