Bandgap and exciton binding energies in lead-iodide-based natural quantum-well crystals

Abstract

We have performed optical absorption and electroabsorption studies on the lead-iodide-based natural quantum-well perovskite-type crystals with different well width (C 6 H 13 NH 3 ) 2 (CH 3 NH 3 ) m21 Pb m I 3mþ1 . With decreasing well thickness, m; the resonance energies of the lowest-energy excitons shift to higher energy due to the increase of the bandgap. The binding energies and oscillator strengths of the excitons drastically increase due to the spatial confinement and image charge effect with decreasing m: The bandgap of (C 6 H 13 NH 3 ) 2 (CH 3 NH 3 ) m21-Pb m I 3mþ1 ðm $ 2Þ can be reproduced by the effective-mass approximations, while the effective-mass approach is not valid for (C 6 H 13 NH 3 ) 2 PbI 4 ðm ¼ 1Þ: q

Scaling law for excitons in 2D perovskite quantum wells

“…3d, e). Close to the continuum onset and in our experimental energy range, the optical transitions in RPPs at energies above E G have been assigned 11,14,50 to transitions between the Pb(6 s )-I(5 p ) states in the valence band and Pb(6 p ) states in the conduction band 20,51 . The absorption features A, B and C can be understood as transitions between valence and conduction bands overlapping with the continuum of states from the band-edge exciton.…”

“…However, key fundamental questions remain unanswered in RPPs with n greater than 1, such as the nature of optical transitions, as well as the behavior of Coulomb interactions especially with increasing quantum well thickness. In fact there has been an intense ongoing debate 6–8,11–13 regarding the exact nature of the optical transitions (excitons versus free carriers) in RPPs with large n -values. RPPs with n equals to 1 (excitons at room temperature), 14,15 and 3D perovskites 16 (free carriers at room temperature) are representative of the two limiting regimes at room temperature, but the analysis of the crossover has not been performed.…”

Intriguing Optoelectronic Properties of Metal Halide Perovskites

“…In Figure 16A, the cryogenic absorption spectra of (C 6 H 13 NH 3 ) 2 PbI 4 (n = 1), (C 6 H 13 NH 3 ) 2 (CH 3 NH 3 )Pb 2 I 7 (n = 2), (C 6 H 13 NH 3 ) 2 -(CH 3 NH 3 ) 2 PbI 10 (n = 3), and CH 3 NH 3 PbI 3 (n = ∞) demonstrate the increased E g upon reduction in inorganic layer thickness (n) due to decreased band dispersion and confinement (section 2), as well as the monotonic enhancement of oscillator strength from n = ∞ → n = 1. 223 A relatively continuous modification of optical properties in mixeddimension MHPs was recently shown by Sichert et al for perovskite nanoplatelets prepared using various proportions of CH 3 NH 3 Br and octylammonium bromide (OABr) ( Figure 16B). 170 With increasing OABr content in the precursor solution, structures tended toward a single-layered QW, with n = 1 reached in the absence of CH 3 NH 3 Br.…”

Solid-State Physics Perspective on Hybrid Perovskite Semiconductors

“…1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 23 It is quite tempting to apply effective mass models based on an ultrathin quantum well with finite confinement barriers for carriers, in order to predict quantum confinement effects in layered HOP. 129 In fact, these empirical models predict superlattice (SL) effects that are not observed experimentally or in DFT simulations. 61,128 A first fundamental limitation of such approaches is that the computed energies of the confined charge carriers lie in a range where strong nonparabolicity occurs.…”