  Hybrid two-dimensional perovskites hold considerable promise as
semiconductors for a wide range of optoelectronic applications. Many efforts
are addressed to exploit the potential of these materials by tailoring their
characteristics. In this work, the optical properties and electronic band
structure in three new Dion-Jacobson (DJ) perovskites (PVKs) are engineered by
modulating their structural distortion. Two different interlayer cations: 1-6,
Hexamethylendiammonium, HE, and 3-(Dimethylamino)-1-propylammonium, DMPA, have
been selected to investigate the role of the cation length and the ammonium
binding group on the crystalline structure. This study provides new insights
into the understanding of the structure-property relationship in DJ perovskites
and demonstrates that exciton characteristics can be easily modulated with the
judicious design of the organic cations. DJ PVKs developed in this work were
also grown as size-controlled single crystal microwires through a
microfluidic-assisted synthesis technique and integrated in a nanophotonic
device. The DJ PVK microwire acts as a waveguide exhibiting strong light-matter
coupling between the crystal optical modes and DJ PVK exciton. Through the
investigation of these polariton waveguides, the nature of the double peak
emission, which is often observed in these materials and whose nature is
largely debated in the literature, is demonstrated originating from the hybrid
polariton state.
