Synergistic effects of fluorine, chlorine and bromine-substituted end-capped acceptor materials for highly efficient organic solar cells

Abstract

Non-fullerene small molecules are more attractive due to their adjustable energy levels, easier synthesis, and low cost of production. Novel non-fullerene acceptor designed materials retain the advantages of fullerene derivatives, as well as overcome the disadvantages of fullerene materials. Modification of novel molecules of end-capped groups was involved to improve the optoelectrical properties of acceptor molecules of OSCs. Herein, the optoelectronic properties of four small new acceptor molecules (PA1-PA4), configured according to the A-D-C-D-A scheme, were studied after the modification of the recently synthesized molecule R (IEICO-4F). The newly designed molecules (PA1-PA4) are comprised of 4,4,9,9-tetra-p-tolyl-4,9-dihydro-s-indaceno[1,2-b:5,6-b']dithiophene (as central core), 3-methoxy thiophene as a donor, which is directly attached with different end-capped acceptors. Some geometric parameters like density of states, binding energy, transition density matrix, absorption maxima, charge transfer analysis and frontier molecular orbitals are performed in order to examine the photovoltaic characteristics of newly designed molecules. Designed molecule (PA1) showed the lowest energy band gap (3.30 eV) with a red-shift in the absorption spectrum (λmax = 870.222 nm) in chloroform which revealed a perfect relationship between end-capped acceptor with large electron-withdrawing character through extended conjugation. PA4 exhibited the highest value of Voc (2.73) among all designed molecules to PTB7-Th donor material. Further, molecular electrostatic potential analysis confirmed the efficient designing of newly designed molecules. Results of all analysis suggested that designed molecules are efficient candidates for high performance organic solar cells.