Single-Layer Carbon Nitride as an Efficient Metal-Free Organic Electron-Transport Material with a Tunable Work Function

Abstract

Single-layer carbon nitride (SLCN) is introduced as a metal-free organic electron transport material (ETL) for organic solar cells, delivering a performance comparable to that of the benchmark nanocrystalline ZnO. SLCN is produced in the form of stable aqueous inks and can serve as an efficient electron transport layer for three different types of active layers, showing high stability to photodegradation. A lower conductivity of SLCN films as compared to ZnO is counter-balanced by their higher transparency and lower light scattering losses. The SLCN ETL provides a unique opportunity to tune the work function from ca. −4.1 to −4.6 eV by varying the annealing temperature due to partial thermal oxidation of the SLCN film. The PL band position follows the oxidation-induced changes of the work function allowing PL properties of SLCN to be used to predict the PV efficiency. The 2D structure of SLCN coupled with unique structural and compositional variability, and tunability of the work function show a high promise for emerging organic PV devices.