Electron-to Hole Transport Change Induced by Solvent Vapor Annealing of Naphthalene Diimide Doped with Poly(3-Hexylthiophene)

Abstract

Herein we report on fabrication and properties of organic field-effect transistors (OFETs) based on the spray-coated films of N,N′-dioctyl naphthalene diimide (NDIC8) doped with 2.4 wt% of poly (3-hexylthiophene) (P3HT). OFETs with the untreated NDIC8:P3HT films revealed electron conductivity [μe* = 5 × 10–4 cm2×(Vs)−1]. After the annealing in chloroform vapor the NDIC8:P3HT films revealed the hole transport only [μh* = 0.9 × 10–4 cm2×(Vs)−1]. Due to the chemical nature and energy levels, the hole transport was not expected for NDIC8-based system. Polarized optical- and scanning electron microscopies indicated that the solvent vapor annealing of the NDIC8:P3HT films caused a transition of their fine-grained morphology to the network of branched, dendritic crystallites. Grazing incidence wide-angle X-ray scattering studies indicated that the above transition was accompanied by a change in the crystal structure of NDIC8. The isotropic crystal structure of NDIC8 in the untreated film was identical to the known crystal structure of the bulk NDIC8. After the solvent annealing the crystal structure of NDIC8 changed to a not-yet-reported polymorph, that, unlike in the untreated film, was partially oriented with respect to the OFET substrate.

Synthesis, Solution, and Solid State Properties of Homological Dialkylated Naphthalene Diimides—A Systematic Review of Molecules for Next-Generation Organic Electronics

“…Obviously, because of unequilibrated crystal morphology and a mismatch between gold work function (−5.1 eV) and HOMO/LUMO levels of NDIs (approx. −7.2 eV/−3.6 eV, respectively), our methodology did not allow reaching the highest possible μ e or the lowest possible threshold voltage (V th ) numbers [ 20 , 70 , 71 , 73 ]. On the other hand, however, our approach enabled a direct comparison between all NDIs in the studied range.…”

“…The OFET based on the N,N′ -dicyclohexyl-2,6-naphthalene NDI revealed electron mobility reaching as high as 6 cm 2 × V −1 × s −1 [ 7 , 16 , 17 , 18 ]. NDIs have been successfully used to enhance the electronic performance of polymer-based OFETs [ 19 , 20 , 21 ]. Lithium-ion batteries with NDI-based electrodes revealed discharge potentials ranging from 2.3 to 2.9 V [ 22 ].…”

In Situ Monitoring the Face-on to Bimodal Texture Transition of P(NDI2OD-T2) during Side-Chain Selective Solvent Vapor Annealing

“…It has been reported that the intrinsic chemical structure of the polymers, involving side-chain steric hindrance − and backbone coplanarity, ,, and processing factors, such as solvents, , coating methods, film drying speed, , and substrate modifications, , both are capable of bringing about profound alterations in molecular orientation. Melt-annealing (thermal annealing above the melting point with subsequent slow cooling) has been found to be a useful post-treatment to achieve dramatic orientation change, resulting in edge-on dominated films. − In comparison, another routine post-treatment, solvent vapor annealing (SVA), has been commonly utilized to improve molecular ordering, but few considerations for its application in controlling molecular orientation. − SVA offers remarkable advantages: simplicity, low cost, free of the possibility of thermal decomposition of semiconductor materials, and less restrictions in the choice of substrate . Moreover, the interactions between the annealing solvent and polymers, including solvent–side chain and solvent–backbone interactions, could be expected to serve as an effective driving force for molecular reorientation. − Thus, SVA is a promising candidate to achieve an orientation transition.…”