Designing Potential Donor Materials Based on DRCN5T with Halogen Substitutions: A DFT/TDDFT Study

Area of Science:

• Materials Science
• Organic Electronics
• Computational Chemistry

Background:

• Organic solar cells (OSCs) offer a promising alternative to traditional silicon-based photovoltaics.
• DRCN5T, an oligothiophene, has demonstrated high power conversion efficiency (PCE) in OSCs.
• The impact of halogenation on DRCN5T's photovoltaic properties remains largely unexplored.

Purpose of the Study:

• To theoretically investigate the effects of halogenation on DRCN5T.
• To design and evaluate novel halogenated DRCN5T derivatives for improved OSC performance.
• To understand the structure-property relationships governing photovoltaic characteristics.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Time-Dependent DFT (TD-DFT) for electronic structure and spectra.
• Analysis of molecular properties including dipole moments, orbital energies, absorption spectra, exciton binding energy (Eb), singlet-triplet energy gap (ΔEST), and electrostatic potential (ESP).
• Estimation of open circuit voltages (VOCs) in OSCs with PC71BM acceptor.

Main Results:

• Generally, halogen substitutions increase the open circuit voltage (VOC).
• Exciton binding energy (Eb) increases with fluorine substitution, while it shows a mixed trend with chlorine and bromine.
• Singlet-triplet energy gap (ΔEST) consistently increases with more halogen substitutions.
• Absorption spectra in the visible region are enhanced for DRCN5T2F, DRCN5T4F, DRCN5T6F, and DRCN5T2Cl.
• Averaged electrostatic potential (ESP) generally increases with halogenation, except for bromine substitutions.

Conclusions:

• Halogenation of DRCN5T can significantly tune its electronic and optical properties.
• DRCN5T2Cl, DRCN5T4F, and DRCN5T6F are identified as promising donor materials for OSCs.
• Theoretical insights guide the rational design of next-generation organic photovoltaic materials.