Computational and Experimental Approach to Understanding the Structural Interplay of Self-Assembled End-Terminated Alkanethiolates on Gold Surfaces

Applications of self-assembled monolayers (SAMs) on surfaces are prevalent in modern technologies and drives the need for a better understanding of the surface domain architecture of SAMs. To explore structural interaction at the interface between gold surfaces and a hydroxyl-terminated alkanethiol, 11-hydroxy-1-undecanethiol, (C11TH) we have employed a combined computational and experimental approach. Density functional theory (DFT) calculations were carried out on the thiol–gold interface using both the Perdew–Burke–Ernzerhof (PBE) and van der Waals (optB86b) density functionals. Our ab initio molecular dynamics (AIMD) simulations revealed that the interface consists of four different distinguished phases, each with different C11TH orientations. Experiments involved deposition of C11TH SAMs onto gold, with the resultant surfaces examined with X-ray photoelectron spectroscopy (XPS) and ellipsometry. Weighted average projected density of states (PDOS) of the different phases were photoionization cross section corrected and these were confirmed by experimental XPS data. Computed molecular parameters including tilt angles and the thickness of SAMs also agreed with the XPS and ellipsometry results. Hydrogen bonding arising from the terminal hydroxyl groups is the primary factor governing the stability of the four phases. Experimental results from XPS and ellipsometry along with DFT simulation results provide insights into the formation of the different orientations of SAM on Au(111) which will guide future efforts in the self-assembled SAMs architecture for other thiols or metal substrates

Optoelectronic Properties of C60 and C70 Fullerene Derivatives: Designing and Evaluating Novel Candidates for Efficient P3HT Polymer Solar Cells

Ten novel fullerene-derivatives (FDs) of C60 and C70 had been designed as acceptor for polymer solar cell (PSC) by employing the quantitative structure-property relationship (QSPR) model, which was developed strategically with a reasonably big pool of experimental power conversion efficiency (PCE) data. The QSPR model was checked and validated with stringent parameter and reliability of predicted PCE values of all designed FDs. They were assessed by the applicability domain (AD) and process randomization test. The predicted PCE of FDs range from 7.96 to 23.01. The obtained encouraging results led us to the additional theoretical analysis of the energetics and UV-Vis spectra of isolated dyes employing Density functional theory (DFT) and Time-dependent-DFT (TD-DFT) calculations using PBE/6-31G(d,p) and CAM-B3LYP/6-311G(d,p) level calculations, respectively. The FD4 is the best C60-derivatives candidates for PSCs as it has the lowest exciton binding energy, up-shifted lowest unoccupied molecular orbital (LUMO) energy level to increase open-circuit voltage (VOC) and strong absorption in the UV region. In case of C70-derivatives, FD7 is potential candidate for future PSCs due to its strong absorption in UV-Vis region and lower exciton binding energy with higher VOC. Our optoelectronic results strongly support the developed QSPR model equation. Analyzing QSPR model and optoelectronic parameters, we concluded that the FD1, FD2, FD4, and FD10 are the most potential candidates for acceptor fragment of fullerene-based PSC. The outcomes of tactical molecular design followed by the investigation of optoelectronic features are suggested to be employed as a significant resource for the synthesis of FDs as an acceptor of PSCs

Designing Thiadiazoloquinoxaline-Based Conjugated Polymers for Efficient Organic Photovoltaics: A DFT/TDDFT Study

Clean and renewable energy development is becoming frontier research for future energy resources, as renewable energy offers sustainable and environmentally friendly alternatives to non-renewable sources such as fossil fuels. Among various renewable energy sources, tremendous progress has been made in converting solar energy to electric energy by developing efficient organic photovoltaics. Organic photovoltaic materials comprising conjugated polymers (CP) with narrow optical energy gaps are promising candidates for developing sustainable sources due to their potentially lower manufacturing costs. Organic semiconductor materials with a high electron affinity are required for many optoelectronic applications. We have designed a series of organic semiconductors comprised of cyclopentadithiophene as a donor and thiadiazoloquinoxaline (TQ) as an acceptor, varying the π-conjugation and TQ-derivatives. We have employed density functional theory (DFT) and time-dependent DFT (TDDFT) to evaluate the designed CP’s optoelectronic properties, such as optical energy gap, dipole moment, and absorption spectra. Our DFT/TDDFT result shows that the energy gap of CPs is lowered and redshifted in the absorption spectra if there is no insertion of conjugation units such as thiophene and selenophene between donor and acceptor. In addition, selenophene shows relatively better redshift behavior compared to thiophene. Our work also provides rational insight into designing donor/acceptor-based CPs for organic solar cells