posted on 2024-01-10, 15:03authored byRanjan Das, Diptikanta Swain, Arup Mahata, Deepak Prajapat, Sanjay Kumar Upadhyay, Sourav Saikia, V. Raghavendra Reddy, Filippo De Angelis, D. D. Sarma
Intense research activities have been exploring the possibility
of harnessing solar energy via photovoltaic and photocatalytic applications
of ferroelectric materials using the built-in electric field for an
efficient separation of photoexcited charge carriers. However, one
of the most important bottlenecks in these efforts is to find ferroelectricity
in suitably low-band-gap materials for harvesting a sizable part of
the solar spectrum, with most of the known ferroelectric materials
having band gaps larger than 2.5 eV. In the present work, we show
that the known chiral and polar compound, (R-/S-MBA)2CuCl4, with MBA = α-methyl
benzylamine, is also ferroelectric and its ligand-to-metal charge
transfer (LMCT) band gap (∼2.53 eV) can be systematically decreased
via substitution of Cl– with Br– forming the solid solution (R-/S-MBA)2CuCl4–xBrx. These compounds retain their chiral ferroelectric
state until x = 2 and reach a significantly low band
gap of ∼2.09 eV for (R-/S-MBA)2CuCl2Br2, which is the smallest
band gap reported so far among layered hybrid ferroelectric materials.
We elucidate the origin of the band gap reduction and other changes
in the electronic structure with the help of state-of-the-art electronic
structure calculations. Chiral ferroelectrics constitute an interesting
class of materials, with ferroelectricity being able to discriminate
between electron and hole charge transports, while chirality may have
the ability to discriminate between up- and down-spin transports.