Enhanced Performance of Polymer Photodetectors Using a Metal-Doped Zinc Oxide Interfacial Layer

Organic photodetectors (OPDs) are cheaper and more flexible than conventional photodetectors based on inorganic precursors, but their wider commercial application is limited by their low electron extraction efficiency under reverse bias conditions (when operating under photoconductive mode). Zinc oxide (ZnO) has shown promise as an electron transport layer for OPDs owing to its wide band gap, but its electron extraction efficiency has been limited by issues such as photoinstability and the formation of surface detects. This study investigated the effects of doping ZnO nanoparticles with indium gallium (i.e., Indium gallium zinc oxide (IGZO)) and ytterbium gallium (i.e., Ytterbium gallium zinc oxide (YGZO)) on the electron extraction efficiency, conductivity, and dark current suppression of the resulting OPD. Both dopants blended uniformly into the sol-gel ZnO framework, which reduced the roughness and improved the surface properties. Compared with ZnO, both IGZO and YGZO slightly shifted the absorption spectra and reduced the dark current density while improving the specific detectivity under reverse bias conditions. We introduce a metric called the Jones factor (JF) as the ratio of the specific detectivity under zero bias conditions to the specific detectivity under reverse bias conditions. Both IGZO and YGZO had much lower JF values than ZnO, which indicates that their specific detectivity drops much less than that of ZnO when the OPD shifts from photovoltaic mode (i.e., zero bias) to photoconductive mode (i.e., reverse bias). Thus, they are potentially better materials for the electron transport layer of the OPDs with a higher electron extraction efficiency.