Environmentally-Stable High Work Function Titanium Carbide MXene for Large-Area Organic Light-Emitting Diodes

This paper presents a transparent conducting electrode (TCE), which is an environmentally-stable two-dimensional titanium carbide (Ti₃C₂T_x, MXene) that has a high work function WF. High-temperature annealing reduced the d-spacing of Ti₃C₂T_x from 1.33 to 1.06 nm; the result was a highly-compacted thin film that can resist inward diffusion of moisture intercalants. The MXene had high WF = 5.84 eV, which is the highest yet; it was achieved by p-type molecular doping using perfluorosulfonic acid. With benefits from the highly compacted structure of Ti₃C₂T_x and superior chemical stability of overcoated PFSA, the p-doped Ti₃C₂T_x exhibited only a 4.8% increase in sheet resistance with WF maintained > 5.60 eV even after 22-day exposure to ambient air. Lastly, the Ti₃C₂T_x TCE was successfully applied as the anode for both large-area and ten-by-ten passive matrix flexible organic light-emitting diodes on 6 cm × 6 cm substrates. The significant increases in environmental stability and WF provides a new method to develop practical applications of MXene as TCEs for optoelectronics and photovoltaics.