  The application of ultrathin two-dimensional (2D) perovskites in
near-infrared and visible-range optoelectronics has been limited owing to their
inherent wide bandgaps, large excitonic binding energies and low optical
absorption at higher wavelengths. Here, we show that by tailoring interfacial
band alignments via conjugation with low-dimensional materials like monolayer
transition metal dichalcogenides (TMD), the functionalities of 2D perovskites
can be extended to diverse, visible-range photophysical applications. Based on
the choice of individual constituents in the 2D perovskite/TMD
heterostructures, our first principles calculations demonstrate widely tunable
type-II band gaps, carrier effective masses and band offsets to enable an
effective separation of photogenerated excitons for enhanced photodetection and
photovoltaic applications. In addition, we show the possibilities of achieving
a type-I band alignment for recombination based light emitters as well as a
type-III configuration for tunnelling devices. Further, we evaluate the effect
of strain on the electronic properties of the heterostructures to show a
significant strain tolerance, making them prospective candidates in flexible
photosensors.
