Stable n-type organic small-molecule conductor enabled by chemically doped ternary components†

Chemical doping is a versatile method for tuning the optoelectronic properties of organic semiconductors (OSCs). Compared to p-type doping, achieving stable and efficient n-type doping in OSCs, especially in small molecules, remains a significant challenge. The lack of a universal doping strategy, along with OSCs having deep lowest unoccupied molecular orbital (LUMO) energy levels and high electron mobility, limits the development of n-type doped OSCs. In this work, a ternary system containing the small-molecule OSC 2DQTT-o, with a deep LUMO level and high electron mobility, the n-type dopant N-DMBI, and the polar insulating polymer PEO was developed. With the introduction of PEO, the miscibility, doping level and doping stability were significantly improved. Notably, the ternary doped components showed excellent air stability, retaining 82% of the initial electrical conductivity after exposure to air for 240 h, representing a 32% improvement compared to the system without PEO. Furthermore, the ternary doped films exhibited good thermal stability, retaining 55% of the initial electrical conductivity after heating at 200 °C. In contrast, the two-component doped films decomposed and became insulating.