Tuning optoelectronic properties of indandione-based D-A materials by malononitrile group acceptors: A DFT and TD-DFT approach

Context

Indandione-based materials are promising candidates for organic electronics, offering high electron mobility and tunable optoelectronic properties. In this study, we explore the optoelectronic and photovoltaic properties of indandione-based donor–acceptor (D-A) materials, specifically (R1) and (R2), by introducing malononitrile group acceptors into their molecular structure. These strong electron-withdrawing acceptors are designed to enhance charge transfer and overall material performance. The designed molecules (DM1–DM4) exhibit a low optical band gap of approximately 1.77 eV, significantly lower than the reference materials (R1 and R2) at around 2.24 eV in a solvent environment. Among the designed molecules, DM4 stands out with superior photovoltaic parameters, including a narrow optical band gap (1.77 eV), higher electron affinity (3.49 eV), an extended excited state lifetime (10.0 ns) owing to its low electron and hole reorganization energies (λ_e ~ 0.13 eV and λ_h ~ 0.24 eV), and improved short-circuit current density (J_sc) of ~ 15.73 mA/cm². Notably, DM4 achieves a power conversion efficiency (PCE) of ~ 18.5%, making it an excellent candidate for device applications.

Method

A comprehensive computational investigation was carried out on indandione-based D-A materials with malononitrile group acceptors (DM1–DM4) using density functional theory (DFT) and time-dependent DFT (TD-DFT) methods, as implemented in Gaussian 16 software. We examined the electronic and optical properties of the proposed molecules through frontier molecular orbital (FMO) analysis, UV–Vis absorption spectra, density of states (DOS), exciton binding energy (E_b), and transition density matrix (TDM) analysis, utilizing GaussView 6.0 and Multiwfn 3.8 software. The photovoltaic parameters and power conversion efficiency (PCE) were evaluated using the Scharber and Alharbi models.