Charge transport and prototypical optical absorptions in functionalized zinc phthalocyanine compounds: A density functional study

Abstract

Metal phthalocyanines are considered to be prominent candidates for designing organic semiconductors. However, enhancing n‐type characteristics and air stability in these compounds have been the major challenges. Earlier studies on zinc phthalocyanines (ZnPc) reported enhancement in electron mobility due to fluorination. We present a theoretical study of the charge transfer and optical properties of functionalized zinc phthalocyanines (XZnPc, with X = F16, Cl16, Br16, I8, and (CN)8) within the framework of the density functional theory. Substitutions with electron‐withdrawing groups at the peripheral sites of ZnPc was found to lower both EHOMO and ELUMO in the compounds. Computed values of electron affinity (EA) > 3 eV in all XZnPcs indicated effective electron injection inferring enhanced n‐type characteristics and air stability in these compounds. However, cyanation ((CN)8), as compared to the other EWGs, is found to enhance the electron mobility more prominently in the compound. In addition, studied optical absorption spectra of all XZnPc compounds at different exchange‐correlation functionals such as B3LYP, PBE0, CAM‐B3LYP, wB97xD, M06, and M06‐2X exhibited Q‐band in visible region (∼600‐700 nm) and B‐band (Soret) in ultraviolet (∼300‐400 nm) region, and a few shows an N‐band below 300 nm. Upon functionalization, the B‐band and Q‐band maxima show bathochromic shift both in gas phase and dimethyl sulfoxide. All these optical absorptions were found to be prototypical in nature, and the spectra are assigned to π→π∗ character.

Controlling energy levels and Fermi level en route to fully tailored energetics in organic semiconductors

“…Tuning the energetic offset between host and dopant can be achieved by molecular modification, through means such as halogenation 14,15 . However, this method is limited to discrete changes in energy.…”

Designing Organic Electron Transport Materials for Stable and Efficient Performance of Perovskite Solar Cells: A Theoretical Study

“…In this context, metal phthalocyanines (MPcs) may be a suitable candidate for ETLs in PSCs due to their unique properties, such as kinetic and thermal stability, considerable charge mobility, suitable band gap, and hydrophobicity in nature. 7 MPcs had been given a considerable attention due to their applications in organic solar cells and thin film transistors. 7 Most of the MPcs show an ideality factor, greater barrier height, and large series resistance.…”

“… 7 MPcs had been given a considerable attention due to their applications in organic solar cells and thin film transistors. 7 Most of the MPcs show an ideality factor, greater barrier height, and large series resistance. In a study, 15 the authors carried out density functional theory (DFT) calculations to explore the electronic structure and bonding in MPcs (M = Fe, Co, Ni, Cu, Zn, and Mg).…”

Chlorosubstituted Copper Phthalocyanines: Spectral Study and Structure of Thin Films

“…Similarly to unsubstituted and fluoro-substituted derivatives, chloro-substituted metal phthalocyanines exhibit semiconductor properties. According to DFT calculations, the HOMO and LUMO energy levels of CuPcCl x decrease in comparison with unsubstituted CuPc derivatives [26,27]. Koshy et al [28] investigated the effect of annealing temperature on the optical band gap of FePcCl 16 films, and considered their possible applications as active layers of molecular electronic devices.…”