One‐step Fabrication of π‐Conjugated Polymer Thin Films from Naphthalenes via Plasma Polymerization for Efficient Optoelectronic Devices: White Polymer Light‐emitting Diodes

Abstract

We describe a facile one‐step fabrication process of thin film conjugated polymers for efficient optoelectronic devices from naphthalenes by plasma polymerization through a new monomer feeding method. The resulting 3‐D aromatic chain networks of the polymerized films were in good agreement with the predictions based on monomer bond rupture routes analysis. The photoluminescence (PL) spectra of plasma‐polymerized films featured short‐lived inter‐molecular emissions arising from self‐assembly of the naphthalene units in the crosslinked architectures. When functioning between the electrodes for light emitting, the plasma films manifested electroluminescence (EL) spectra that showed a steep rise at the threshold wavelength red‐shifted relative to the PL spectra, indicating prevailing charge tunneling to lower excited states by the accumulated interfacial charges. The wide distribution of conjugation lengths in the plasma films provided the subsequent energy transfer routes and gave rise to the broad EL emission band that produced stable pure white light of CIE coordinates of (0.34, 0.33) with excellent efficiencies. This dry deposition process allows the use of multiple monomers for property tailoring and may be used for large‐area depositions.

Electroluminescence and Photoluminescence of Conjugated Polymer Films Prepared by Plasma Enhanced Chemical Vapor Deposition of Naphthalene

“…These defects have destructive effects on the efficiency of optoelectronic devices. [8,9] On the other hand, chemical vapor deposition (CVD) and Plasma Enhanced CVD (PECVD) are solventfree processes to form polymer directly from starting monomers. [8] Among these, PECVD is a unique technique for fabrication of high quality and chemically stable thin films.…”

“…[12,14,15] In the past, some few works have been done about plasma polymerization of naphthalene using RF frequency. One more recent work is C.Chang et.al [9] study on RF plasma polymerization of 1-ethylnaphthalene.…”

“…Therefore, polymer chains started to be formed as the highly cross-linked polymer. [9] Optical emission spectroscopy (OES) was applied during the plasma polymerization for more understanding about the plasma environment. Figure 2 shows the OES spectra corresponding to different plasma powers.…”

“…Figure 4 illustrates FTIR spectra of the PPN films at different powers. All FTIR spectra showed bands at 780 and 3050 cm-1 that are related to out-of-plane aromatic C-H bending vibration and aromatic C-H stretching vibration, respectively [6,9,[21][22][23][24]. The peaks in 1500-1600 cm-1 region corresponds to C=C stretching bonds [9].…”

“…All FTIR spectra showed bands at 780 and 3050 cm-1 that are related to out-of-plane aromatic C-H bending vibration and aromatic C-H stretching vibration, respectively [6,9,[21][22][23][24]. The peaks in 1500-1600 cm-1 region corresponds to C=C stretching bonds [9]. Also, aliphatic C-H stretching peaks at 2924 cm-1 due to methylene and 2856 cm-1 due to methyl groups and aromatic C-H stretching vibration at 3050 cm-1 were detected in plasma polymerized films [21,24].…”