Beyond the 2D Field‐Effect Charge Transport Paradigm in Molecular Thin‐Film Transistors. (15th August 2022)

• Record Type: Journal Article
• Authors: Benvenuti, Emilia; Portale, Giuseppe; Brucale, Marco; Quiroga, Santiago D.; Baldoni, Matteo; MacKenzie, Roderick C. I.; Mercuri, Francesco; Canola, Sofia; Negri, Fabrizia; Lago, Nicolò; Buonomo, Marco; Pollesel, Andrea; Cester, Andrea; Zambianchi, Massimo; Melucci, Manuela; Muccini, Michele; Toffanin, Stefano
• Is Part Of: Advanced Electronic Materials. Volume 9:Number 1(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-15
• Subjects: charge transport -- crystallite orientation -- oligothiophenes -- organic field‐effect transistors -- out‐of‐plane crystalline domains; Materials -- Electric properties -- Periodicals; Materials science -- Periodicals; Magnetic materials -- Periodicals; Electronic apparatus and appliances -- Periodicals; 537
• DOI: 10.1002/aelm.202200547
• Languages: English
• ISSNs: 2199-160X

Abstract

Abstract: Organic field‐effect transistors (OFETs) are considered almost purely interfacial devices with charge current mainly confined in the first two semiconducting layers in contact with the dielectric with no active role of the film thickness exceeding six to eight monolayers (MLs). By a combined electronic, morphological, structural, and theoretical investigation, it is demonstrated that the charge mobility and source–drain current in 2, 20‐(2, 20‐bithiophene‐5, 50‐diyl)bis(5‐butyl‐5 H ‐thieno[2, 3‐ c ]pyrrole‐4, 6)‐dione (NT4N) organic transistors directly correlate with the out‐of‐plane domain size and crystallite orientation in the vertical direction, well beyond the dielectric interfacial layers. Polycrystalline films with thickness as high as 75 nm (≈30 MLs) and 3D molecular architecture provide the best electrical and optoelectronic OFET characteristics, highlighting that the molecular orientational order in the bulk of the film is the key‐enabling factor for optimum device performance. X‐ray scattering analysis and multiscale simulations reveal the functional correlation between the thickness‐dependent molecular packing, electron mobility, and vertical charge distribution. These results call for a broader view of the fundamental mechanisms that govern field‐effect charge transport in OFETs beyond the interfacial 2D paradigm and demonstrate the unexpected role of the out‐of‐plane domain size and crystallite orientation in polycrystalline films to achieve optimum electronic and optoelectronic properties in organic transistors. Abstract : Evidence is reported that the interfacial 2D paradigm used to describe the field‐effect charge transport in organic field‐effect transistors must be overcome. The out‐of‐plane molecular packing and orientational order in the bulk of polycrystalline films must be taken into account to design organic transistors with optimized electronic and optoelectronic properties.