  Here, we design a novel class of Janus structures PbXY(X,Y = F, Cl, Br, I)
and propose it for the solar mediated photocatalytic water splitting hydrogen
production as well as for the photovoltaic solarcell applications. Charge
analysis shows that covalent bonding for less electronegative atoms and ionic
bonding for more electronegative atoms. Strong dual bonding like ionic one side
and covalent other side is observed when heavy and lighter atoms are part of
the same Janus structures. The as designed Janus structures show good dynamical
stability through phonon calculations. Basic electronic structure using
Generalised Gradient Approximation(GGA) reveal both direct and indirect nature
of band gap with large tunability. Heyd-Scuseria-Ernzerhof (HSE) electronic
structure calculations are performed and wider band gaps are predicted for
these Janus structures. The calculated effective masses of charge carriers show
robust charge carrier dynamics. The orbital resolved electronic density of
states (DOS) shows that the conduction band edge is composed of pz orbital of
Pb atom. The partialcharge density calculated at conduction band minimum (CBM)
also support the result obtained from PDOS analysis. Breaking of
centrosymmetry, polarization in the out of plane direction, the z-oriented
orbitals of CBM all points that these materials are suitable for shift current
generation. The calculated optical absorption spectra show that the Janus
structures are suitable for visible light absorption. The calculated potential
difference between the top and bottom layer show significant variation and
maximum (1.02 eV) is observed for PbClF. Further, we show that combining both
potential difference and HSE bandgap, valence band maximum(VBM) and CBM
straddle the water redox potentials, thus making the Janus structures suitable
for water redox reactions.
