Kinetics of Bias stress and Bipolaron Formation in Poly(thiophene)

TL;DR

This study investigates the kinetics of bias-stress effects and bipolaron formation in poly(thiophene) thin film transistors, revealing temperature-dependent behaviors and different bipolaron populations affecting device stability.

Contribution

It provides new insights into bipolaron formation rates, their temperature dependence, and the mechanisms of bias-stress effects in poly(thiophene) transistors.

Findings

Bipolaron formation rate is proportional to the square of hole concentration.

Maximum bipolaron formation occurs near 220 K.

A separate long-term bias-stress effect suggests different bipolaron populations.

Abstract

Studies of the kinetics of the bias-stress effect are reported for PQT-12 polymer thin film transistors. We associate the bias-stress effect with bipolaron formation, based on the observation that the stressing rate is proportional to the square of the hole concentration. The bipolaron formation rate is measured as a function of temperature, and the thermal dissociation rate is also deduced from the data. We discuss the hole capture process and suggest that tunneling through the Coulomb barrier dominates. The temperature dependence of bipolaron formation and recovery kinetics leads to a maximum in their formation at about 220 K, and we also find other changes in the electrical properties near this temperature. A separate bias-stress effect is observed to operate at much longer time scales, and might be associated with a different population of bipolarons.