Correlations between Mechanical and Electrical Properties of Polythiophenes

The elastic moduli of polythiophenes, regioregular poly(3-hexylthiophene)(P3HT) and poly-(2,5-bis(3-alkylthiophene-2-yl)thieno[3,2-b]ithiophene) (pBTTT), are compared to their field effect mobility showing a proportional trend. The elastic moduli of the films are measured using a buckling-based metrology, and the mobility is determined from the electrical characteristics of bottom contact thin film transistors. Moreover, the crack onset strain of pBTTT films is shown to be less than 2.5%, whereas that of P3HT is greater than 150%. These results show that increased long-range order in polythiophene semiconductors, which is generally thought to be essential for improved charge mobility, can also stiffen and enbrittle the film. This work highlights the critical role of quantitative mechanical property measurements in guiding the development of flexible organic semiconductors.