Ultrathin P(NDI2OD‐T2) Films with High Electron Mobility in Both Bottom‐Gate and Top‐Gate Transistors

Abstract

Ultrathin organic films (typically < 10 nm) attracted great attention due to their (semi)transparency and unique optoelectronic properties that benefit applications such as sensors and flexible electronics. At the core of that, achieving high mobility in an ultrathin film is essential for the efficient operation of relevant electronic devices. While the state‐of‐the‐art material systems, e.g., P(NDI2OD‐T2) also known as N2200 can achieve high mobility in a thin film (typically > 20 nm), multitudinous challenges remain in processing an ultrathin film exhibiting desired charge transport morphology within a preferred thickness limit. Here, high electron mobility (a tenfold increase compared to annealed spin‐coated films) is reported in both the top and bottom‐gate configuration organic field‐effect transistors comprising ultrathin N2200 films produced with a water‐floating film transfer method. A range of characterization techniques are used to investigate these ultrathin films and their microstructure, and conclude that favorable edge‐on polymer orientation at the top as well as throughout the ultrathin film thickness and the quality of π–π ordering as captured by the largest coherences length resulted in this high mobility in N2200 ultrathin films, in stark contrast to the commonly observed microstructural gradient in spin‐coated thin films. The results provide new insight into the electronic and microstructural properties of thin films of organic semiconductors.

Contributions of Polymer Chain Length, Aggregation and Crystallinity Degrees in a Model of Charge Carrier Transport in Ultrathin Polymer Films

“…All of the films revealed thickness ranging from 5.7 to 8.0 nm, whether cast from fresh or aged solution. Such thickness justifies considering the films as ultrathin. , Casting the films out of fresh solutions of P3HT, P3HTT10, or P3HTT20 resulted in formation of films with rather granular morphology (Figure ). Similarly, as previously reported for P3HT and other conjugated polymers, , the solution aging caused formation of remarkable fibrillar morphologies (Figure ).…”

“…14,15 One of the relatively recent issues in organic electronics is the fabrication of devices with ultrathin (i.e., thinner than 10 nm) active films. 3,27,28 The optical transparency and mechanical properties of the ultrathin films make them good candidates for intrinsically flexible, transparent devices. 28−31 The geometry of the ultrathin films may impart quasi-twodimensional (quasi-2D) charge carrier transport and can minimize charge carrier trapping because of the absence of the electronically inert bulk.…”

“…One of the relatively recent issues in organic electronics is the fabrication of devices with ultrathin (i.e., thinner than 10 nm) active films. ,, The optical transparency and mechanical properties of the ultrathin films make them good candidates for intrinsically flexible, transparent devices. − The geometry of the ultrathin films may impart quasi-two-dimensional (quasi-2D) charge carrier transport and can minimize charge carrier trapping because of the absence of the electronically inert bulk. ,, Hence, replacing conventional thin films with ultrathin films can be a strategy to maximize the performance and reduce the costs of materials for fabrication of organic electronic devices. However, successful formation of high-performance ultrathin film-based devices was relatively rarely reported so far .…”

Unidirectionally Aligned Donor–Acceptor Semiconducting Polymers in Floating Films for High‐Performance Unipolar n‐Channel Organic Transistors

“…In this case, films are often prepared using a high‐boiling‐point solvent, such as CB or xylene, on a Petri dish and have no preferential alignment (Figure S1, Supporting Information). [ 8,19,27,34 ]…”

“…The average value of µ e ∥ films was fabricated in a BGTC structure with Au electrodes because Au is often preferred as a contact for S/D electrodes for P(NDI2OD‐T2). [ 19,25,26,38,39,51–53 ] The average µ e ∥ and µ e ⊥ values of the P(NDI2OD‐T2) films prepared with CF were 0.19 ± 0.08 and 0.066 ± 0.009 cm 2 V –1 s –1 , respectively. In contrast, the average µ e ∥ and µ e ⊥ in devices prepared with CF:CB solvent blend were 0.44 ± 012 and 0.15 ± 0.08 cm 2 V –1 s –1 , respectively.…”