A High-Performance p-Doped Conducting Polymer Blend Based on Sulfonated Polyalkoxythiophene and Poly(4-hydroxystyrene)

Understanding the fundamental mechanisms of electrical degradation or instability in organic semiconductor devices is a key step toward their rational design for higher performance and more demanding applications. Here we report the successful suppression of the conductivity fade phenomenon that occurs in doped conducting polymers when they are stress-biased with a large electric field or current density. While poly(3,4-ethylenedioxythiophene) :poly(styrenesulfonic acid) (PEDT:PSSH) shows a relatively low threshold to conductivity fading, the recently developed sulfonated poly{thiophene-3-[2-(2-methoxyethoxy)ethoxy]-2,5-diyl}:poly(4-hydroxystyrene) (S-P3MEET:PHOST), which is an intimate blend of S-P3MEET and PHOST, is far more resilient. In situ UV-vis, Raman, and Fourier-transform infrared spectroscopies reveal that the doping level across S-P3MEET:PHOST films remains remarkably stable when they are driven at high dc biases. Spectroelectrochemical Raman measurements suggest that both S-P3MEET and S-P3MEET:PHOST are also less susceptible to electrochemical dedoping than PEDT:PSSH. Comparison of the conductivity fading characteristics of S-P3MEET in the presence or absence of PHOST, however, reveals a large matrix effect. We obtained evidence that the enhanced electrical stability of S-P3MEET:PHOST results from its inherent ultralow ionic conductivity, further suppressed by a serendipitous scavenging of excess sulfonic acid protons on S-P3MEET through a solid-state esterification reaction with PHOST during annealing. The shutdown of the ionic conductivity cuts off the coupled ion transfer processes needed to cause a doping level shift in the film. This affords a practical means of suppressing the electrically induced doping level instability in doped conducting polymer systems.