Effects of ladder structure on the electronic properties and field-effect transistor performance of Poly(benzobisimidazobenzophenanthroline)

A comparative study of the semi-ladder (BBB) and ladder (BBL) forms of poly(benzobisimidazobenzophenanthroline) and their binary blends shows that the ladder structure endows a smaller optical bandgap, greater electron delocalization and substantially enhanced electron transport. n-Channel organic field-effect transistors (OFETs) fabricated from the semi-ladder BBB were found to have an electron mobility of 1.5x10(-3) cm(2)/V whereas similar ladder BBL OFETs had an electron mobility of 2.2x10(-2) cm(2)/V, which is a 15-fold enhancement in electron transport in favor of the full ladder polymer analogue. The BBB and BBL OFETs had similar good stability in ambient air while their electrical characteristics were successfully simulated by using a SPICE model, revealing dramatically reduced source/drain contact resistance in the BBL devices. Compared to its ladder analogue BBL, semi-ladder BBB has been rarely studied in semiconductor devices, and hence the present observation of high electron mobility in BBB thin films with good stability in air suggest that it is also promising for developing various electronic and energy conversion/storage devices.