  As emphasized in a recent review article [Chem. Rev. 122, 14180 (2022)],
organic solar cell (OSC) photoconversion efficiency has been rapidly evolving
with results increasingly comparable to those of traditional inorganic solar
cells. Historically, OSC performance improvement focused first on the
morphology of P3HT:PC61BM solar cells then went through different stages to
shift lately interest towards nonfullerene acceptors (NFAs) as a replacement of
PC61BM acceptor (ACC) molecule. Here, we use density-functional theory (DFT)
and time-dependent (TD) DFT to investigate four novel NFAs of A-D-A
(acceptor-donor-acceptor) form derived from the recently synthesized IDIC-4Cl
[Dyes and Pigments 166, 196 (2019)]. Our level of theory is carefully evaluted
for IDIC-4Cl and then applied to the four novel NFAs in order to understand how
chemical modifications lead to physical changes in cyclic voltammetry (CV)
frontier molecular orbital (FMO) energies and absorption spectra in
solution.Finally we design and apply a new type of Scharber plot for NFAs based
upon some simple but we think reasonable assumptions. Unlike the original
Scharber plots where a larger DON band gap favors a larger PCE, our modified
Scharber plot reflects the fact that a smaller ACC band gap may favor PCE by
filling in gaps in the DON acceptor spectrum. We predict that only the
candidate molecule with the least good acceptor A, with the highest frontier
molecular orbital energies, and one of the larger CV lowest unoccupied
molecular orbital (LUMO) highest unoccupied molecular orbital (HOMO) gaps, will
yield a PM6:ACC PCE exceeding that of the parent IDIC-4Cl ACC. This candidate
also shows the largest oscillator strength for the primary 1 (HOMO,LUMO)
charge-transfer transition and the largest degree of delocalization of charge
transfer of any of the ACC molecules investigated here.
