Observation of Negative Charge Trapping and Investigation of Its Physicochemical Origin in Newly Synthesized Poly(tetraphenyl)silole Siloxane Thin Films

Abstract

A new kind of organic-inorganic hybrid polymer, poly(tetraphenyl)silole siloxane, was invented and synthesized for realization of its unique charge trap properties. The organic portions consisting of (tetraphenyl)silole rings were responsible for negative charge trapping, while the Si-O-Si inorganic linkages provided the intrachain energy barrier for controlling electron transport. The polysilole siloxane dielectric thin films were fabricated by spin-coating and curing of the polymers, followed by characterization with spectroscopic ellipsometry (SE), near edge X-ray absorption fine structure spectroscopy (NEXAFS), and photoemission spectroscopy (PES). The abrupt increase in density and decrease in thickness of the thin film at a curing temperature of 100 °C was attributed to a thermodynamically preferred state in the nanoscopic arrangement of the polymer chains; this was due to cofacial π-π interactions in a skewed manner between peripheral phenyl groups of the (tetraphenyl)silole rings of the adjacent polymer chains. Using the NEXAFS spectrum to assess high electron affinity, the LUMO energy level of the dielectric thin film cured at 150 °C was positioned 1 eV above the Fermi energy level (E(F)). The electron trapping of the dielectric thin films was confirmed from the positive flat band shift (ΔV(FB)) in the capacitance-voltage (C-V) measurements performed within the metal-insulator-semiconductor (MIS) device structure, which strongly verified the polymer design concept. From the simple kinetics model of the electron transport, it was proposed that the flat band shift (ΔV(FB)) or trap density of the negative charges (|ρ|) was logarithmically proportional to the decay constant (β) for the electron-tunneling process. When a phenyl group of a silole ring in a polymer chain was inserted into the two available phenyl groups of another silole ring in another polymer chain, the electron transfer between the groups was enhanced, decreasing the trap density of the negative charges (|ρ|). For the thermodynamically preferred state generating the high refractive index, the distance between the two phenyl groups of the adjacent polymer chains was estimated to be in the range of 0.27-0.36 nm.

Synthesis of Alternating Copolysiloxane with Terthiophene and Perylenediimide Derivative Pendants for Involatile WORM Memory Device

“…According to the operating mechanism of the PTSi‐alt‐PDISi based memory device, electrical field induced conformation change and the charge transfer interaction between pendent terthiophene donor and perylenediimide acceptor moieties could explain the electrical switching behavior of PTSi‐alt‐PDISi appropriately. Several literatures have reported the electrical bistability of some non‐conjugated polymers with pendant active groups . For example, memory effects of PVK derivatives with flexible spacers between the carbazole pendant group and the polymer backbone, in which regiorandom and regioregular alignments corresponds to the low and high conductivity states, only showed WORM or volatile features.…”

Polyphenylsilole multilayers – an insight from X-ray electron spectroscopy and density functional theory

“…3.1 XPS X-ray photoelectron spectroscopy was used to characterise the polyphenylsilole multilayers with elemental and chemical sensitivity. In particular, XPS is perfectly suited to study the number and type of chemical species present in the sample, thanks to the known relationship between the measured binding energies and the oxidation state of silicon atoms 28,29 in different compounds. Thus, the growth of HPS (Fig.…”

Oligosiloxane Functionalized with Pendant (1,3‐Bis(9‐carbazolyl)benzene) (mCP) for Solution‐Processed Organic Electronics

“…There are literature precedents for the electrical bistability of some non-conjugated polymers with pendant active groups. [49][50][51] For example, memory effects of PVK derivatives with flexible spacers between the carbazole pendant group and the polymer backbone, [16,17] in which regio-random and regio-regular alignments correspond to the low-and high-conductivity states, showed only WORM or volatile features. Similarly, different stable conformations of ODCzMSi with high or low conductivity states could be obtained under the action of electric field through the p-p stacking alignment of its pendent aromatic groups inducing the electrical switching performance.…”