A Comparative Study of the Semiconductor Behavior of Organic Thin Films: TCNQ-Doped Cobalt Phthalocyanine and Cobalt Octaethylporphyrin

Abstract

The structure formed by cobalt phthalocyanine (CoPc) and cobalt octaethylporphyrin (CoOEP) with electron-acceptor tetracyano-π-quinodimethane (TCNQ), was studied by Density Functional Theory (DFT) methods. According to theoretical calculations, both cobalt systems can establish dispersion forces related to TCNQ and also in both cases the link between them is built by means of hydrogen bonds. Based on the results of these DFT calculations, we developed experimental work: the organic semiconductors were doped, and the thermal evaporation technique was used to prepare semiconductor thin films of such compounds. The structure of the films was studied by FTIR and Raman spectroscopy. The optical properties of the CoPc-TCNQ and CoOEP-TCNQ films were investigated by means of UV-Vis measurements. The results obtained were used to estimate the type of transitions and the optical bandgap. The results were compared to the previously calculated theoretical bandgap. The CoOEP-TCNQ film presented the smallest theoretical and experimental bandgap. Finally, the electrical properties of the organic semiconductors were evaluated from a PET (polyethylene terephthalate)/indium tin oxide (ITO)/cobalt macrocycle-TCNQ/silver (Ag) device we prepared. The CoOEP-TCNQ-based device showed an ohmic behavior. The device manufactured from CoPc-TCNQ also showed an ohmic behavior at low voltages, but significantly changed to SCLC (space-charge limited conductivity) at high voltage values.

Fabricación y caracterización de semiconductores poliméricos basados en Ftalocianina Verde

“…En este sentido, las bandas B y Q se asocian directamente a las transiciones 𝜋−𝝅 * , mismas que surgen de la estructura de la CuPc. Por un lado, la banda-B se identifica como las transiciones electrónicas 𝜋−𝝅 * , dentro de los orbitales 𝒂 𝟐𝒖 y 𝒃 𝟐𝒖 , mismos que van al LUMO 𝒆 𝒈 (Farag, 2007), (Lee et al, 2010), (Sánchez-Vergara et al, 2020). Por otro lado; la banda-Q, que se divide en dos picos, se encuentra asignada a las mismas transiciones electrónicas 𝜋−𝝅 * del HOMO al LUMO, aunque correspondientes a los orbitales 𝒂 𝟏𝒖 al orbital 𝒆 𝒈 (Farag, 2007), (Sánchez-Vergara et al, 2020), (Socol et al, 2016).…”

“…𝟏 𝟐 de la energía del fotón (ℎ𝜈) (Mali et al, 2012), (Urbach, 1953). Para ello, los datos de absorción se acoplan al comportamiento del modelo de Tauc (Sánchez-Vergara et al, 2020):…”

“…El coeficiente de absorción (𝛼) y la frecuencia (𝑣), se obtienen a partir de la transmitancia, la absorbancia y la longitud de onda, obtenidos por el espectro de UV-Vis. Con respecto a la ecuación anterior, G es una constante que depende de la probabilidad de transición y ℎ la constante de Planck; del mismo modo, 𝐸 𝑔 𝑜𝑝𝑡 es la brecha de la banda prohibida óptica, mientras que r, es el número que caracteriza las transiciones, siendo r= ½ y r=2, para transiciones electrónicas directas e indirectas respectivamente (Mali et al, 2012), (Sánchez-Vergara et al, 2020), (Urbach, 1953). Con respecto al band gap de la película de PMMA-CuP green, se calculó a partir de 𝛼 y hν para transiciones indirectas, debido al carácter amorfo de la película PMMA-CuPc green.…”

Recent Developments in Stimuli Responsive Smart Materials and Applications: An Overview

“…Many green building solutions with heat dissipation, wastewater systems and energy efficiency are included in this study. Also included is a solar powered cooling system [43,44] technology ability to collect construction data. In order to help India accomplish its long-term sustainability goals, the study will make recommendations on the best procedures and materials to use in the country [45].…”