End-capped modification of dithienosilole based small donor molecules for high performance organic solar cells using DFT approach

Abstract

Considering the worth of molecular designing, A-D-A type four small donor (SM1-SM4) photoactive materials comprised of DTS core, substituted with push-pull acceptors at terminal sites linked through bithiophene units were investigated. In present project, detailed theoretical consideration under DFT and TD-DFT methods (CAM functional/basis set 6-31G) was given-to explore wavelength dependent (absorption maxima, first excitation energy, light harvesting efficiency), electronic (FMO, DOS, TDM), reactivity (IP, EA, MEP), and charge transfer parameters (Voc, FF) of selected molecules (SM1-SM4) in systematic way. All novel molecules revealed broadening of absorption maxima and lessening of band gaps comparative to absorption coefficient and energy difference between HOMO/LUMO of RM due to electron pulling nature of acceptor groups. Greater dipole moment of all designed chromophores in excited state suggests their good solubility in solvent medium (chloroform) as compared to gaseous medium. Furthermore, charge transfer dynamics in terms of internal hole and electron reorganization energies give lower values which indicate higher transfer abilities for SM2 and SM1 respectively. Excellent output results for modelled molecules interpreted through open circuit voltage (with PC61BM) and fill factor, predict rise in PCE value than already reported molecule. Out of class, SM4 molecule emerged as an ideal photovoltaic material on account of better optical properties, easy electronic transitions, enhanced chemical reactivity, fast charge conductivity, and high estimated PCE. Eventually, these encouraging results favors the structural modeling of small molecules achieved through effective combination of end-capped moieties. We look forward that this entire work may provide strong theoretical guidelines, aids in designing and amplifying the optoelectronic features of proposed frameworks on vast scale than reference.