Organic photovoltaics (OPVs) are
fast emerging as an attractive
alternative to resolve the future energy crisis by maximum harness
of solar energy. The optically active layer of OPVs consists of a
p-type polymer as the donor and an n-type molecule as the acceptor.
The efficiency of the polymeric donor material is decided by the type
of monomeric units and nature of side groups attached to the backbone
of the polymeric chain. This study focuses on the polymeric structures
of polythiophene and its analogues, polyfuran and polyselenophene,
to explore the relationship between structure and electronic/optical
properties via static and time-dependent density functional calculations.
Each polymer chain is substituted with a variety of electron releasing/accepting
side groups to understand their influence on the band gap and energy
shifting of frontier orbitals with respect to a well-known acceptor
(phenyl-C70-butyric acid methyl ester (PC70BM)).
All the underlying physical processes starting from excitation of
an electron from the HOMO of the donor material to its LUMO, breaking
of exciton into free charge carriers, and diffusion of a free electron
and hole to the donor–acceptor interface have been investigated
thoroughly. The photovoltaic efficiency has been interpreted in terms
of electronic (E
gap) and optical (E
exe) band gap, open circuit voltage (V
OC), and short circuit current density (J
SC). The reported derivatives have E
gap in the range 1.69–2.78 eV which enables exciton
generation by photon absorption in the visible region. It has been
concluded that while electron-donating groups result in maximum lowering
of E
gap, the CN-substituted derivatives
exhibit maximum efficiency with a V
OC of
about 1.63–1.75 eV.
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