Evaluating metal-free pyrene-centered donor dye via terminal group to enhance PCE of organic solar cells: A DFT approach

Abstract

In this work, we presented the end-capped group modification of the previously reported metal-free pyrene-based dye, focusing on the improved efficiency of OSCs. By using theoretical design, we created a series of donor molecules (PA1-PA8) with a pyrene core to enhance their photophysical and photovoltaic properties. Using DFT and time-dependent DF T with the ωB97XD functional and 6-311G(d,p) basis set, we evaluated various properties such as frontier molecular orbitals, partial density of states, optical properties (λmax), excitation energy, oscillator strength, charge mobility, dipole moment, light harvesting efficiency, fill factor, open-circuit voltage, transition density matrix, binding energies, excitation energies and molecular electrostatic potential. The computational analysis revealed that all newly fabricated compounds showed a bathochromic shift in the absorption spectrum, with λmax values ranging from 350 to 420 nm, in contrast to the reference compound (357 nm) in dichloromethane. The designed molecules demonstrated favorable characteristics, including lower reorganization energies (indicating improved charge transport capability), and a narrower band gap with reduced excitation and binding energies. Notably, PA4 with (Z)-2-(5-ethylidene-3-methyl-4-oxothiazolidin-2-ylidene)malononitrile group in its acceptor moiety, shows improved photovoltaic properties with band gap 5.722 eV, binding energy (2.374 eV), Voc (5.623 eV), fill factor (0.976), and LHE (0.996). Furthermore, we investigated the donor-acceptor blend of the most favorable designed molecule i.e., PA4 alongside the recognized acceptor PC71BM. The electron density in this blend demonstrated an effective electronic population transfer from donor (PA4) to acceptor (PC71BM). Moreover, PA1-PA8 exhibit the capacity to promote donor characteristics, making them promising candidates for the progression of more proficient PV devices.