High‐Mobility Naphthalene Diimide and Selenophene‐Vinylene‐Selenophene‐Based Conjugated Polymer: n‐Channel Organic Field‐Effect Transistors and Structure–Property Relationship

Abstract

Interdependence of chemical structure, thin-film morphology, and transport properties is a key, yet often elusive aspect characterizing the design and development of high-mobility, solution-processed polymers for large-area and flexible electronics applications. There is a specific need to achieve >1 cm 2 V −1 s −1 field-effect mobilities (μ) at low processing temperatures in combination with environmental stability, especially in the case of electron-transporting polymers, which are still lagging behind hole transporting materials. Here, the synthesis of a naphthalene-diimide based donor-acceptor copolymer characterized by a selenophene vinylene selenophene donor moiety is reported. Optimized field-effect transistors show maximum μ of 2.4 cm 2 V −1 s −1 and promising ambient stability. A very marked film structural evolution is revealed with increasing annealing temperature, with evidence of a remarkable 3D crystallinity above 180 °C. Conversely, transport properties are found to be substantially optimized at 150 °C, with limited gain at higher temperature. This discrepancy is rationalized by the presence of a surface-segregated prevalently edge-on packed polymer phase, dominating the device accumulated channel. This study therefore serves the purpose of presenting a promising, high-electron-mobility copolymer that is processable at relatively low temperatures, and of clearly highlighting the necessity of specifically investigating channel morphology in assessing the structure-property nexus in semiconducting polymer thin films.

Effect of Backbone Sequence of a Naphthalene Diimide-Based Copolymer on Performance in n-Type Organic Thin-Film Transistors

“…The ICT bands from the solution to the film state were slightly blue-shifted, and the absorption spectrum of the film annealing was widened as the annealing temperature increases. These results were contrary to the previous results of PNDI-TVT and PNDI-SVS. , Furthermore, the maximum absorption of PNDI-TVT and PNDI-SVS in the film state showed at 403 and 400 nm for the π–π* transition and 716 and 748 nm for the intramolecular charge transfer band, respectively. The PNDI-VTV (PNDI-VSV) was slightly blue-shifted compared with PNDI-TVT (PNDI-SVS).…”

Resonant X‐Ray Diffraction of Conjugated Polymers at the Selenium K‐Edge

“…The presence of ( h 00) peaks in these transmission WAXS images suggests a “face‐on” orientation of crystallites, which is confirmed by GIWAXS images provided in the Supporting Information. These 2D GIWAXS images also evidence that both polymers exhibit a relatively high degree of crystalline order and similar microstructure to previous reports [27, 28]. Figure 2c,d presents radially‐averaged 1D line profiles extracted from the 2D WAXS patterns in Figure 2a,b.…”

Diffractive X-ray Waveguiding Reveals Orthogonal Crystalline Stratification in Conjugated Polymer Thin Films

“…The current measurement is sensitive to much longer range variations, measuring 2 ± 2 nm of thickness variations over the illuminated sample. The AFM additionally revealed a fibrillar morphology and well-defined step heights (previously published and discussed), consistent with a high degree of surface order and high level of edge-on orientation at the surface. This relatively low level of roughness together with the extremely low divergence of the X-ray beam is important in resolving the details in Figure .…”