Electrical Properties of Pyrolyzed and Electrochemically Lithium-Doped Poly(hydrazocarbonyl-1,4-phenylenecarbonyl) Film

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Abstract
The carrier transport and detailed carbonization processes of pristine (poly (hydrazocarbonyl-1,4-phenylenecarbonyl):PHP) film have been investigated as a function of heat-treatment temperature (HTT). Formation of (poly(1,3,4-oxadiazole-2,5-diyl-1,4-phenylene):POP) at HTT=400°C is confirmed and explained by the dehydration reaction of PHP molecular structure. Conductivity (σ) increases by 20 orders of magnitude from 10-18 S/cm with HTT of 1000°C. The enhancement of σ with HTT up to 600°C has been interpreted by the increase of localized charge carrier and the most prominent effect of the enhancement of σ by HTT above 800°C has been explained by not only the increase of carrier density but also the increase of mobility. Even in the sample of low HTT ( <500°C), σ is enhanced and its activation energy decreases upon electrochemical Li doping. On the other hand, in the sample of high HTT ( 800–1000°C) σ decreases slightly and its activation energy increases. Electrical conduction in the sample of low HTT ( <600°C) is explained by three-dimensional variable range hopping (3D-VRH). On the other hand, in the nondoped and Li-doped sample of high HTT ( ≥600°C), the conduction process is explained by taking both 3D-VRH and metallic conduction processes into consideration.