Newly efficient designed benzothiadiazole (A-D-A-D-A topology) based materials for organic photovoltaics: DFT Study

Abstract

A series of fifteen small-donor molecules (R1- R15) based on acceptor-donor-acceptor-donor-acceptor (A-D-A-D-A) topology has been designed and investigated theoretically, by introducing three different cores (benzodithiophene, [1,2,5] thiadiazole and [3,4] quinoxaline) and π-spacers (cyclopentadithiophene, 2-(thiophene-2-yl)− 1 H-pyrrole and 2, 5-bithiazole) in the reference molecule (R). Computational analysis is based on the DFT and TD-DFT levels of theory. Herein, our findings confirmed that molecules having [3,4] quinoxaline core unit along with various π-spacers bithienyl (R3), cyclopentadithiophene (R7), 2-(thiophene-2-yl)− 1 H-pyrrole (R11) 2, 5-bithiazole (R15) exhibited narrow energy gap value 1.37, 1.23, 1.34 and 1.56 eV, respectively. Moreover, their absorption spectra are shifted towards UV-Visible and NIR regions at 885 nm, 972 nm, 885 nm, and 791 nm, respectively. Almost all donors display extraordinarily enhanced spectral responses and yield good hole (λh) and electron (λe) transporting values range from 0.132 to 0.231 and 0.162–0.275 eV, respectively. The predicted electron and hole mobility values for R7 are μe= 6.4 × 10-3 and μh= 1.18204 cm2/Vs, respectively. The Voc value ranges from 0.43 V to 1.62 V and the predicted power conversion efficiency PCE value of designed donors ranges from ∼2% - ∼13%. Interestingly, the R15 molecule shows an impressive PCE of over 13%. Thus, our computational studies provide a deep insight to confirm that among all R1, R2, R3, R5, R6, R7, R9, R10, R11, R13, R14, and R15 show extraordinary results than R. Hence, they would be a promising candidate on the base of orbital energy levels, λmax, PCEs values and photo physical properties which has been compared with the suggested PCBM acceptor for OSCs.