The effect of the dielectric end groups on the positive bias stress stability of N2200 organic field effect transistors

TL;DR

This study investigates how dielectric end groups affect bias stress stability in N2200 organic transistors, finding that end groups have minimal impact, but long annealing significantly improves device stability and mobility independence from gate voltage.

Contribution

It is the first to examine the influence of dielectric end groups on bias stress stability in high-performing N2200 transistors, revealing minimal effect of end groups and highlighting annealing as a key factor.

Findings

Dielectric end groups do not affect bias stress stability.

Long annealing enhances stability and reduces gate dependence of mobility.

Most stable devices show weak or no dependence of mobility on gate voltage.

Abstract

Bias stress degradation in conjugated polymer field-effect transistors is a fundamental problem in these disordered materials and can be traced back to interactions of the material with environmental species,1,2,3 as well as fabrication-induced defects.4,5 However, the effect of the end groups of the polymer gate dielectric and the associated dipole-induced disorder on bias stress stability has not been studied so far in high-performing n-type materials, such as N2200.6,7 In this work, the performance metrics of N2200 transistors are examined with respect to dielectrics with different end groups (Cytop-M and Cytop-S8). We hypothesize that the polar end groups would lead to increased dipole-induced disorder, and worse performance.1,9,10 The long-time annealing scheme at lower temperatures used in the paper is assumed to lead to better crystallization by allowing the crystalline domains to reorganize in the presence of the solvent.11 It is hypothesized that the higher crystallinity could narrow down the range at which energy carriers are induced and thus decrease the gate dependence of the mobility. The results show that the dielectric end groups do not influence the bias stress stability of N2200 transistors. However, long annealing times result in a dramatic improvement in bias stress stability, with the most stable devices having a mobility that is only weakly dependent on or independent of gate voltage.