In-Situ Monitoring of the Solid-State Microstructure Evolution of Polymer:Fullerene Blend Films Using Field-Effect Transistors

Abstract

Organic fi eld-effect transistors (OFETs) are used to investigate the evolution of the solid-state microstructure of blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C 61 -butyric acid methyl ester (PC 61 BM) upon annealing. Changes in the measured fi eld-effect mobility of holes and electrons are shown to reveal relevant information about the phase-segregation in this system, which are in agreement with a eutectic phase behavior. Using dualgate OFETs and in-situ measurements, it is demonstrated that the spatialand time-dependence of microstructural changes in such polymer:fullerene blend fi lms can also be probed. A percolation-theory-based simulation is carried out to illustrate how phase-segregation in this system is expected to lead to a substantial decrease in the electron conductivity in an OFET channel, in qualitative agreement with experimental results.

Impact of Fullerene Molecular Weight on P3HT:PCBM Microstructure Studied Using Organic Thin‐Film Transistors

“…[ 31 ] We hence consider our observation of a reduction in electron mobility as a useful indicator that phase-segregation is taking place, rather than suggest that phase-segregation leads to a reduction of electron mobility in OPV structures. [ 31 ] By studying the conditions under which the electron mobility falls in such OFET devices, it is hoped that information relevant to OPV fabrication and optimization can be elucidated. Upon annealing at 220 ° C the hole mobility starts to fall and the electron mobility begins to recover.…”

“…[ 31 ] The p-and n-channel transfer characteristics of an un-annealed P3HT:PC 71 BM (1:1 wt%) BCBG ambipolar OFET are shown in Figure 1 (b). With gold source and drain electrodes, such polymer:fullerene OFETs are known to be capable of injecting and transporting holes in the polymer network and electrons in the fullerene network, but not nice-versa.…”

“…This aggregation is understood to lead to a reduction in the concentration of the methanofullerene in the regions between clusters [ 34 ] and hence a reduction in percolation pathways for electrons, leading to a fall in electron mobility. [ 31 ] Whilst detrimental to ambipolar OFET performance, it is understood that this phase-segregation will conversely lead to an improvement in carrier transport for both holes and electrons in OPV devices. [ 18 ] This apparent inconsistency is easily explainable by considering the signifi cant differences in device/ architecture geometry, and hence how phase-segregation will affect the fullerene-percolation pathways in these systems.…”

“…[28][29][30][31] It has similarly been shown that by using bilayer P3HT:PC 61 BM structures, the diffusion of PC 61 BM in P3HT can also be studied via OFET mobility measurements. [ 27 ] Despite differences in the device architecture and interfaces of OPVs and OFETs, such measurements can provide a unique and innovative way to investigate the properties of polymer:fullerene systems.…”

Techniques for characterization of charge carrier mobility in organic semiconductors

“…13). 124 They used FET measurements on P3HT/PCBM blends annealed at different temperatures and reported that the hole and electron mobilities remain constant till the annealing temperature of 140 C. However, upon annealing above this temperature, the hole mobility increases while the electron mobility drastically decreases. The observed effect was attributed to the increased crystallization in the P3HT domains and the increased clustering of PCBM.…”