The quantum-confined Stark effect in layered hybrid perovskites mediated by orientational polarizability of confined dipoles

G Walters,S Hoogland,A Amassian,M Wei,O Voznyy,E Sargent,D.-M Smilgies,A Kiani,R Munir,R Quintero-Bermudez

doi:10.1038/s41467-018-06746-5

Abstract

The quantum-confined Stark effect (QCSE) is an established optical modulation mechanism, yet top-performing modulators harnessing it rely on costly fabrication processes. Here, we present large modulation amplitudes for solution-processed layered hybrid perovskites and a modulation mechanism related to the orientational polarizability of dipolar cations confined within these self-assembled quantum wells. We report an anomalous (blue-shifting) QCSE for layers that contain methylammonium cations, in contrast with cesium-containing layers that show normal (red-shifting) behavior. We attribute the blue-shifts to an extraordinary diminution in the exciton binding energy that arises from an augmented separation of the electron and hole wavefunctions caused by the orientational response of the dipolar cations. The absorption coefficient changes, realized by either the red- or blue-shifts, are the strongest among solution-processed materials at room temperature and are comparable to those exhibited in the highest-performing epitaxial compound semiconductor heterostructures.

Highlights

The quantum-confined Stark effect (QCSE) is an established optical modulation mechanism, yet top-performing modulators harnessing it rely on costly fabrication processes
We demonstrate that layered perovskites can be engineered to have QCSE shifts, either to the red or blue, that produce absorption coefficient changes up to 70 cm−1 for 56 kV cm−1 applied electric fields
The strength of the field-induced optical changes observed for our nanoplatelets, which reach absorption coefficient changes of 70 cm−1 for 56 kV cm−1 applied fields, are the largest reported for thin-film materials at room temperature (Supplementary Table 3)

Summary

Introduction

The quantum-confined Stark effect (QCSE) is an established optical modulation mechanism, yet top-performing modulators harnessing it rely on costly fabrication processes. For an exciton resonance with Gaussian broadening, the amplitudes of the absorption changes, Δα, related to a Stark shift induced by an electric field, F, are proportional to the factors that define the shape of the transition’s optical absorption, and the alignment of the quantum wells with the electric field. Á cos2φ Γ ð1Þ where the oscillator strength, f, and binding energy, EB, determine the amplitude of the optical transition; the linewidth, Γ, determines its breadth; and the orientational order parameter is defined by the angle, φ, between the direction of confinement and the applied field In light of these properties, we hypothesized that layered perovskites could be engineered to produce large modulation amplitudes through the QCSE

Methods

Results

Conclusion