Abstract:
Indigo-based structures were designed with the help of density-functional theory (DFT) and
proposed as potential hole-transporting materials (HTMs) for tin-based and mixed-metal perovskite
solar cells (PSCs). First, theoretical methodology was benchmarked to determine the most
appropriate functionals for optimization and calculation of the energies of indigo-based structures,
using reference structures with known energies. A linear mathematical model was built based on
calculations of reference structures, to estimate and predict actual energy levels of indigo-based
molecules. It was shown that GSOPv is a good estimation of actual HOMO energy for indigoid
structures. Next, the influence of position of attachment of new substituents on the final HOMO
energy was studied and used for design of new structures. Indigoids with alkoxy and alkylamine
groups attached at 5,5’- positions, as well as asymmetric structure with cyclic and alkylamine groups
attached, were demonstrated to have suitable energetics for application as HTMs for CsSnI3 and
MASn0.5Pb0.5I3 PSCs.