Designing of asymmetric non-fullerene based acceptor materials by re-modification of π-spacers with PCE > 20 % for organic solar cell

Abstract

In this study, four new organic molecules with different compounds called the π-linkers, embedded between dithieno[3,2-b:2′,3′-d]pyrrole donor core and dicyanoindanone end-capped acceptor molecules were theoretically designed and analyzed to be proposed as the new asymmetric small molecule acceptors (SMAs) with the highest power conversion efficiency (PCE) in non-fullerene organic solar cells (OSCs). The charge transportability, stability, electronic, and optical properties were calculated based on the molecular structure analysis with the density functional theory (DFT) approach and the results were compared with dithieno[3,2-b:2′,3′-d]pyrrole based asymmetric SMAs named TPIC with dicyanoindanone end-capped groups. As a result of efficient π-π stacking, the energy differences decreased by 17.71 % and the charge transport increased by 49 %. The molecules showed broad absorption spectra ranging from 400 nm to 1200 nm with significant redshifted wavelength towards the near IR region coupled with low excitation energies. The LUMO energy level of the external donor PM7 is aligned with HOMO energy levels of the architecture acceptor molecules via bandgap tuning and the open-circuit voltage (VOC) increased from 1.002 V to 2.44 V for the highest combination PM7:C4. The efficacious charge transport properties, high excitonic generation with low excitation energies, facile separation, and increased VOC via band-gap tunning; all four designed molecules achieved a champion PCE ranging from 20 % to 34 % at short circuit current density 9, 12, and 15 mA cm−2. The molecules exhibited the highest PCE value for any asymmetric non-fullerene small molecule acceptor-based organic solar cells.