Assessing the Electrical Characteristics of p–n Heterojunction Prototype Diodes Realized with n-Type Polyimide Materials

Abstract

Three new aromatic polyimides with donor–acceptor topology consisting of electron-donating ortho-catenated triphenylamine (TPA) modified with two trifluoromethyl (CF3) groups and electron-accepting naphthyl­(di)­imide- or perylenediimide-based moieties were synthesized and thoroughly investigated. Their main physicochemical properties were assessed according to the structural variation of the dianhydride segment. The polymers exhibited advantageous solubility in polar solvents, which allowed their processing into homogeneous thin films under friendly conditions, as well as good thermal stability. The photo-optical activity investigated in detail by UV–vis and fluorescence spectroscopy was finely modulated by the electron-accepting strength of the dianhydride segment, with light emission originating from both monomeric and intramolecular charge transfer transitions, which is otherwise dependent on the polarity of the surrounding solvent molecules. Due to the high electron-accepting characteristics promoted by both CF3 and naphthyl­(di)­imide or perylenediimide, these polymers behaved as n-type materials. The highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies evaluated according to the electrochemical activity suggested the polymers suitability for use in p–n heterojunctions. Thus, to prove the electron transporting capability, prototype diodes have been realized with these polyimides in an indium tin oxide (ITO)­(Al)/poly­(3,4-ethylenedioxythiophene):poly­(styrene sulfonate) (PEDOT:PSS)/polyimide/eGaIn configuration. Their current–voltage characteristics revealed a rectification ratio up to 63, moderate to high shunt resistance, moderate to low series resistance, and moderate current leakages. The charge transport evaluation disclosed the tunneling phenomenon as the main mechanism that drives the realized prototype diodes, with an ideality factor down to 5.48. The nice combined features encountered for these polyimides make them appealing candidates as n-type materials for advanced optoelectronic applications.

Non‐planar polyimides with monomer containing four triphenylamines for near‐infrared electrochromism and TNP detection

“…As shown in Table 1, these PIs have good solubility and can be soluble in many polar organic solvents, such as N ‐methyl‐2‐pyrrolidone (NMP) and N , N ‐dimethylformamide (DMF) at room temperature. The introduction of big bulk TPA block will increase the spacing of PIs 53,54 . At the same time, the methoxy group acts as a flexible aliphatic segment unit, which further improves the solubility 55,56 .…”

“…The introduction of big bulk TPA block will increase the spacing of PIs. 53,54 At the same time, the methoxy group acts as a flexible aliphatic segment unit, which further improves the solubility. 55,56 The introduction of both TPA and methoxy weakens the interaction between main chains of PIs, which increases the solubility and processability in organic solvents while maintaining thermal stability.…”

The Synergistic Effect of Triazine and Phosphaphenanthrene Units on the Physico-Chemical Behavior of Polyimides

“…Thus, researchers have customized the polyimide macromolecular chain in order to obtain materials with specific properties for targeted applications. The approaches that have been undertaken have mainly consisted of incorporating various moieties into the starting monomer’s structure (kink, spiro, cardo, cycloaliphatic, bulky, fluorinated, hetero, carbazole, perylene, chiral, nonlinear optical, or unsymmetrical units), copolymerization reactions, functionalization of the already obtained polyimides, or use of different fillers towards nanocomposite-based polyimide material development [ 5 , 7 , 9 , 10 , 11 , 12 , 13 , 14 ]. It has been proven that the incorporation of aromatic ether and isopropylidene units enables increased processability and lowered glass transition temperature of the corresponding polyimides, while maintaining increased thermal stability [ 15 , 16 , 17 , 18 ].…”