Efficiency enhancement of inverted organic photovoltaic cells due to an embedded Ce-doped ZnO electron transport layer synthesized by using a sol-gel process

Abstract

Ce-doped ZnO layers were synthesized by using a sol-gel method for applications as electron transport layers (ETLs) in inverted organic photovoltaic (OPV) cells. X-ray photoelectron spectroscopy spectra, energy-dispersive X-ray analysis spectra, and atomic force microscopy and scanning electron microscopy images showed that the formed samples were Ce-doped ZnO layers with smooth surfaces. The inverted OPV cell based on a poly (3-hexylthiophene):[6,6]-phenyl C-61 butyric acid methyl ester bulk heterojunction containing a Ce-doped ZnO ETL was fabricated for enhanced efficiency. Current density-voltage results showed that the power conversion efficiency of the fabricated inverted OPV cell with a Ce-doped ZnO ETL was 0.87 times larger than that with a ZnO ETL due to the enhanced absorption of the Ce-doped ZnO ETL at a near-ultraviolet/blue light region between 300 and 500 nm. Device structure and current density-voltage (J-V) characteristic curves for inverted organic photovoltaic (OPV) cells with a ZnO or a Ce-doped ZnO electron transport layer (ETL) under AM 1.5 stimulated illumination at an intensity of 100 mW/cm(2). The enhancement of the power conversion efficiency (PCE) values of the inverted OPV cells with a Ce-doped ZnO ETL is attributed to increases in the short-circuit current density, open-circuit voltage, and fill factor. The results indicate that the PCEs of the ZnO-based OPV cells can be improved by doping Ce into the ZnO layer.