Doping of Conjugated Polythiophenes with Alkyl Silanes

Abstract

A strong modification of the electronic properties of solution‐processable conjugated polythiophenes by self‐assembled silane molecules is reported. Upon bulk doping with hydrolized fluoroalkyl trichlorosilane, the electrical conductivity of ultrathin polythiophene films increases by up to six orders of magnitude, reaching record values for polythiophenes: (1.1 ± 0.1) × 103 S cm−1 for poly(2,5‐bis(3‐tetradecylthiophen ‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) and 50 ± 20 S cm−1 for poly(3‐hexyl)thiophene (P3HT). Interband optical absorption of the polymers in the doped state is drastically reduced, making these highly conductive films transparent in the visible range. The dopants within the porous polymer matrix are partially crosslinked via a silane self‐polymerization mechanism that makes the samples very stable in vacuum and nonpolar environments. The mechanism of SAM‐induced conductivity is believed to be based on protonic doping by the free silanol groups available within the partially crosslinked SAM network incorporated in the polythiophene structure. The SAM‐doped polythiophenes exhibit an intrinsic sensing effect: a drastic and reversible change in conductivity in response to ambient polar molecules, which is believed to be due to the interaction of the silanol groups with polar analytes. The reported electronic effects point to a new attractive route for doping conjugated polymers with potential applications in transparent conductors and molecular sensors.

Formation of inversion layers in organic field-effect transistors

“…It has been reported that the doping level in P3HT can be varied deliberately by changing the exposure time. [17][18][19] The acceptor density ranges between 10 16 -10 17 cm −3 and n i is about 1.6 × 10 4 cm −3 , leading to a predicted maximum depletion depth between 40 and 200 nm. A semiconductor layer thickness of more than 200 nm was chosen, larger than the predicted maximum depletion depth.…”

High Conductivity in Molecularly p‐Doped Diketopyrrolopyrrole‐Based Polymer: The Impact of a High Dopant Strength and Good Structural Order

“…[22] A new doping approach of small conjugated molecules and polymers by fluorinated alkylsilanes was introduced, however the doping of DA copolymers by fluorinated alkylsilanes has not been reported. [23] PDPP(2-OD) 2 TT is one of the benchmark DA copolymers for transistor applications having a hole mobility in 1-10 cm 2 V −1 s −1 range and a HOMO level of about −5.35 eV. It comprises alternating DPP and thieno [3,2-b]thiophene (TT) moieties and C 20 H 41 -solubilizing alkyl chains (solubilizers) having a branching point on the second carbon atom.…”

Doping kinetics of organic semiconductors investigated by field-effect transistors

“…This molecule is reported to yield acid doping of conjugated molecules. 3 We found that the doping process of rr-P3HT with TCFOS is sufficiently slow to measure the doping kinetics. The dopant density is derived from the transfer curves as a function of temperature and exposure time.…”

“…A gas sensor could be envisaged by monitoring the increase in conductance upon exposure to the target analyte. 3 To fabricate a reliable gas sensor it is important to understand the kinetics of the doping process. However, the number of studies on the doping kinetics is limited.…”