Realizing the Potential of ZnO with Alternative Non-Metallic Co-Dopants as Electrode Materials for Small Molecule Optoelectronic Devices

Abstract

High performance indium tin oxide (ITO)-free small molecule organic solar cells and organic light-emitting diodes (OLEDs) are demonstrated using optimized ZnO electrodes with alternative non-metallic co-dopants. The co-doping of hydrogen and fl uorine reduces the metal content of ZnO thin fi lms, resulting in a low absorption coeffi cient, a high transmittance, and a low refractive index as well as the high conductivity, which are needed for the application in organic solar cells and OLEDs. While the established metal-doped ZnO fi lms have good electrical and optical properties, their application in organic devices is not as effi cient as other alternative electrode approaches. The optimized ZnO electrodes presented here are employed in organic solar cells as well as OLEDs and allow not only the replacement of ITO, but also signifi cantly improve the effi ciency compared to lab-standard ITO. The enhanced performance is attributed to outstanding optical properties and spontaneously nanostructured surfaces of the ZnO fi lms with non-metallic co-dopants and their straightforward integration with molecular doping technology, which avoids several common drawbacks of ZnO electrodes. The observations show that optimized ZnO fi lms with non-metallic co-dopants are a promising and competitive electrode for low-cost and high performance organic solar cells and OLEDs.