Organic field-effect transistors based on vapor deposited 2,9-dialkylpentacene films

Organic field-effect transistors based on vapor deposited films of 2,9-diethylpentacene (C-2-PEN), 2,9-dibutylpentacene (C-4-PEN) and 2,9-dioctylpentacene (C-8-PEN) were successfully fabricated. All the alkylpentacene based OFETs showed typical p-channel FET characteristics, and the best field-effect mobility of 4.8 x 10(-2) cm(2)V(-1)s(-1) with on/off current ratio of similar to 10(4) was obtained for the C-2-PEN based OFET. Interestingly, the filed-effect mobility decreased as alkyl-chain length becomes longer. According to the molecular orbital calculations, the 2,9-dialkylpentacenes form doubly bent molecular structures in which the all-anti alkyl groups are not lie on the same plane as that of the pentacene core. The alkyl-chains may hinder the intermolecular interactions and overlap, meaning the poor intermolecular charge transfer.