Elucidating the Role of Side-Chain Polarity of Conjugated Polyelectrolytes by Doping Through Organic Electrochemical Transistor

Conjugated polyelectrolytes (CPEs) exhibit a novel structure composed of electron or hole conducting π-conjugated backbone and ion conducting pendant ionic functionalities. Anionic narrow-band-gap CPE named poly[2,6-(4,4-bis-potassium butanylsulfonate-4H-cyclopenta-[2,1-b;3,4-b0]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBTSO3K, or CPE-K) is well known for self-doped property which is fabricated as a channel material for organic electrochemical transistor (OECT).<br/>In this work, electronic and ionic transport is studied by OECT system. Different types of polarity of side chain attached to the same backbone that contains an alternating D-A units of cyclopentadithiophene (CPDT) and benzothiadiazole (BT) were synthesized. The affect of different polarity was examined as a channel material by using gel-type ionic liquid electrolyte (1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or [EMIM]⁺[TFSI]^-) which allows wider range of gate voltage and constant measurement conditions etc. All three channel materials each showed ON and OFF state both in accumulation and depletion mode only by changing the polarity of gate and drain voltage. Ion transport mechanism was compared through OECT system by measuring transfer/output curve, μC^* value and response time etc. Our work allows for maximizing doping effect through ion penetration and utilize as a dual mode switching system.