Mapping Spatial Variations of Wide Band Gap Perovskite Thin Films

Emily Miller, Kshitiz Dolia, Bailey Frye, Yanfa Yan, Zhaoning Song, Nikolas J. Podraza The University of Toledo, Toledo, OH, United States

Wide band gap FA0.8Cs0.2Pb(I0.65Br0.35)3 perovskites are examined by mapping spectroscopic ellipsometry to determine spatial variations of structural and optoelectronic properties. Complex dielectric function (ε = ε1 + iε2) spectra are highly sensitive to compositional variations, which may inadvertently cause nonuniformities in optical properties across the area of a device. Measurements of partial device-like structure consisting of glass substrate / indium tin oxide / NiOx / Me4-PACz monolayer / perovskite is sensitive to band gap and Urbach energy variations. Band gap values range from 1.77 to 1.80 eV from the sample edge to center. The Urbach energies range between 29 and 50 meV, from center to edge. This approach enables the detection of variations in perovskite material quality characteristics and layer thicknesses, both of are necessary during scale up for large area deposition.