Temperature-insensitive properties are attractive for most of the electronics. However, charges in orderless polymer film are transported following thermally activated hopping mode and influenced by defects. Temperature dependence is unavoidable in polymeric field-effect transistors (PFET) and how to overcoming this shortcoming seems impossible to accomplish.
In a study published in Chem, the research group led by Prof. LIU Yunqi and GUO Yunlong from Institute of Chemistry, Chinese Academy of Sciences (ICCAS) developed a stable electron-transporting PFET, which can work from 200 K (-73 ℃) to 460 K (187 ℃) with a mobility of higher than 3.5 cm²V^-1s^-1.
The researchers use polyacrylonitrile (PAN, Tg ～85 ℃) as additive to control the pre-aggregation of N2200 polymer (P(NDI2OD-T2)) in solution state. The bar-coating process forced N2200 polymers to form thermodynamically stable molecular packing and orientation of linear gains in polymeric films. It improved the mobility of N2200 from 0.30 cm²V^-1s^-1 to 5-6 cm²V^-1s^-1 at room temperature.
The electron mobilities of their FETs are kept 5-6 cm²V^-1s^-1 from 300 K (25 ℃) to 460 K (187 ℃). The researchers believe that great crystallinity of the polymer film, ordered thermodynamics-stable molecular packing mode and less defects should be the key points for getting stable electron-transporting PFET.
Even in the PFET killer region at 200 K (-73℃), the mobility of their device was still higher than 3.5 cm²V^-1s^-1, not as the directly mixed N2200/PAN showed more than 1 order of magnitude decreasing of mobility. It means that their PFETs own working ability at extremely cold or hot zone (such as work in the South Pole about 191-290 K and the Lut desert about 253-344 K).
This study might break people's traditional understanding towards organic devices, which suffers from low performance and insufficient stability.
This work entitled "lignment of linear polymeric grains for highly stable N-type thin-film transistors" was published in Chem (2021, DOI: 10.1016/j.chempr.2021.01.016). 

The schematic diagram of bar coating (Left), OFET device structure and the relationship between mobility and temperature (Right). (Image by Prof. GUO Yunlong)

Contact:
Prof. LIU yunqi or GUO yunlong
Institute of Chemistry, Chinese Academy of Sciences
Email: liuyq@iccas.ac.cn or guoyunlong@iccas.ac.cn