Alloy-based tuning of the bandgap and exciton binding energy in perovskites*

We have used the technique of electroabsorption (EA) to study the exciton binding energy and other properties of 2D metal-halide perovskites (MHPs). EA is a measurement of the difference in absorption between electric field on and off, and in particular can be used as a precise measurement of the bandgap (Eg), and hence also the exciton binding energy (Eb). In this presentation we will include a short introduction to EA and then focus on changes to Eg and Eb that result in PEA₂PbI₄ when alloying Sn with Pb and for using combinations of I, Br, and Cl as the halogen atom. We find evidence of a co-existence of elemental-rich domains within the Pb-Sn and Br-I alloys, and are able to use the Br:Cl ratio of the Br-Cl mixtures, PEA₂Pb(Br_xCl_1-x)₄, to tune the band gap energies continuously between 3.076 and 3.643 eV and the exciton binding energies from 349 meV to 487 meV.