On the Relation between Morphology and FET Mobility of Poly(3‐alkylthiophene)s at the Polymer/SiO₂ and Polymer/Air Interface

Abstract

The influence of the interface of the dielectric SiO2 on the performance of bottom‐contact, bottom‐gate poly(3‐alkylthiophene) (P3AT) field‐effect transistors (FETs) is investigated. In particular, the operation of transistors where the active polythiophene layer is directly spin‐coated from chlorobenzene (CB) onto the bare SiO2 dielectric is compared to those where the active layer is first spin‐coated then laminated via a wet transfer process such that the film/air interface of this film contacts the SiO2 surface. While an apparent alkyl side‐chain length dependent mobility is observed for films directly spin‐coated onto the SiO2 dielectric (with mobilities of ≈10−3 cm2 V−1 s−1 or less) for laminated films mobilities of 0.14 ± 0.03 cm2 V−1 s−1 independent of alkyl chain length are recorded. Surface‐sensitive near edge X‐ray absorption fine structure (NEXAFS) spectroscopy measurements indicate a strong out‐of‐plane orientation of the polymer backbone at the original air/film interface while much lower average tilt angles of the polymer backbone are observed at the SiO2/film interface. A comparison with NEXAFS on crystalline P3AT nanofibers, as well as molecular mechanics and electronic structure calculations on ideal P3AT crystals suggest a close to crystalline polymer organization at the P3AT/air interface of films from CB. These results emphasize the negative influence of wrongly oriented polymer on charge carrier mobility and highlight the potential of the polymer/air interface in achieving excellent “out‐of‐plane” orientation and high FET mobilities.

Precise Control of Lamellar Thickness in Highly Oriented Regioregular Poly(3‐Hexylthiophene) Thin Films Prepared by High‐Temperature Rubbing: Correlations with Optical Properties and Charge Transport

“…A possible reason for this result is that the structure of the films are different at both interfaces, especially in terms of crystallinity. For spin coated films, it is well known that the structure of the P3HT film at the buried interface with the substrate can be significantly different from that in the bulk . It can be anticipated that the P3HT chains located at the SiO 2 interface may have more difficulties to align and crystallize than those chains located at the film interface directly in contact with the rubbing cloth.…”

The Effect of Dopant‐Free Hole‐Transport Polymers on Charge Generation and Recombination in Cesium–Bismuth–Iodide Solar Cells

“…P3TI [38] 100 1.721 .8 10 À3 5.69 3.97 5.29 TQ1 [39,40] 93 1.781 .6 10 À3 5.70 3.92 5.24 P3HT [41][42][43] 75 1.891 0 À4 -10 À1 5.10 3.21 4.63…”

The study of polythiophene/water interfaces by sum-frequency generation spectroscopy and molecular dynamics simulations

“…[89][90][91][92][93] It is worth emphasizing that in most of these studies a 'vertical' configuration was a priori ruled out, assuming the backbone axis c parallel to the surface. Many different studies 66,87-96 have investigated preferential molecular orientation of rr-P3HT thin films in contact with air, highlighting the important role of several processing parameters, including spin coating solvent and speed, annealing time and temperature, regio-regularity and molecular weight.…”