Large Modulation of Charge Carrier Mobility in Doped Nanoporous Organic Transistors

Abstract

Molecular doping of organic electronics has shown promise to sensitively modulate important device metrics. One critical challenge is the disruption of structure order upon doping of highly crystalline organic semiconductors, which significantly reduces the charge carrier mobility. This paper demonstrates a new method to achieve large modulation of charge carrier mobility via channel doping without disrupting the molecular ordering. Central to the method is the introduction of nanopores into the organic semiconductor thin films via a simple and robust templated meniscus-guided coating method. Using this method, the charge carrier mobility of C -benzothieno[3,2-b]benzothiophene transistors is boosted by almost sevenfold. This paper further demonstrates enhanced electron transport by close to an order of magnitude in a diketopyrrolopyrrole-based donor-acceptor polymer. Combining spectroscopic measurements, density functional theory calculations, and electrical characterizations, the doping mechanism is identified as partial-charge-transfer induced trap filling. The nanopores serve to enhance the dopant/organic semiconductor charge transfer reaction by exposing the π-electrons to the pore wall.

High‐Mobility, Solution‐Processed Organic Field‐Effect Transistors from C8‐BTBT:Polystyrene Blends

“…[5,14,21,26,27] Though some recent works report values as high as 16 cm 2 V −1 s −1 [14] and 18 cm 2 V −1 s −1 [27] for solution-processed C8-BTBT, these values are peak values (µ peak ), as indicated in the schematic in Figure S10E (Supporting Information). This resulted in the best performing devices if compared to other technologies with similar material systems.…”

“…[24] Moreover, peak values of 9.1 cm 2 V −1 s −1 were reported for the same blend after recrystallization via solvent-vapor-annealing (SVA). [5,14,23,27,28] This behavior is considered to be caused by gate-voltage-dependent contact resistance, and makes a consistent extraction of mobility values very difficult, rendering a direct comparison of reported mobilities challenging and of limited usefulness. In particular, a mobility of 9.2 cm 2 V −1 s −1 has been extracted from blade-cast devices, prepared by a similar technology as utilized in our work.…”

“…[25] Besides promising results obtained from spin-cast blends of various polymers and C8-BTBT, scalable processing technologies, such as blade coating or zone casting have been utilized for the deposition of C8-BTBT. [9] Specifically, a meaningful comparison of device performance only appears possible for OFETs with identical contact materials, [14,21,26,27] or among the limited instances of reported "ideal" devices, i.e., the ones that seem not to be limited by contact effects. [26] However, due to poor substrate coverage, the value has been corrected for the presumed channel width that is covered with semiconductor.…”

“…In particular, a mobility of 9.2 cm 2 V −1 s −1 has been extracted from blade-cast devices, prepared by a similar technology as utilized in our work. [4,25,29,30] Nonetheless, the current state-of-the-art solution deposition methods that report device performances for C8-BTBT often use silver (Ag) contacts [5,14,21,26,27] and do show gatevoltage-dependent mobilities. Without this correction, the actual effective mobility is between 6 and 7.4 cm 2 V −1 s −1 .…”

“…[26] However, due to poor substrate coverage, the value has been corrected for the presumed channel width that is covered with semiconductor. Therefore, in order to compare our results to previous works that apply shear coating [26,27] and to properly evaluate our progress in optimizing the film coating conditions and film morphologies relative to the existing literature and the coating methods they describe, we also optimized our coating conditions using a bottom-gate, top-contact device architecture with Ag source and drain electrodes ( Figure 1A). In a more recent example that reports uncorrected effective saturation mobility, values around 10.2 cm 2 V −1 s −1 are obtained, after typical defects of zone-cast films have been repaired by lateral homoepitaxy that was templated by a solution-processed single crystalline film.…”