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.