Interconversion between Free Charges and Bound Excitons in 2D Hybrid Lead Halide Perovskites

Abstract

The optoelectronic properties of hybrid perovskites can be easily tailored by varying their components. Specifically, mixing the common short organic cation (methylammonium (MA)) with a larger one (e.g., butyl ammonium (BA)) results in 2-dimensional perovskites with varying thicknesses of inorganic layers separated by the large organic cation. In both of these applications, a detailed understanding of the dissociation and recombination of electron–hole pairs is of prime importance. In this work, we give a clear experimental demonstration of the interconversion between bound excitons and free charges as a function of temperature by combining microwave conductivity techniques with photoluminescence measurements. We demonstrate that the exciton binding energy varies strongly (between 80 and 370 meV) with the thickness of the inorganic layers. Additionally, we show that the mobility of charges increases with the layer thickness, in agreement with calculated effective masses from electronic structure calculations.

Organic–inorganic metal halide hybrids beyond perovskites

“…The value of n can range from 1 to infinity, where the two extremely case with n = ∞ and n = 1 refer to 3D metal halide perovskites and layered-2D perovskites, respectively. Reducing number of layers leads to an increase in band gap due to the stronger quantum confinement [82][83][84] and the increase of the exciton binding energy [85]. Recently, 2D and quasi-2D metal halide perovskites received great research attention for their higher stability than their 3D counterparts [86].…”

Scaling law for excitons in 2D perovskite quantum wells

“…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.…”

Quantifying Charge‐Carrier Mobilities and Recombination Rates in Metal Halide Perovskites from Time‐Resolved Microwave Photoconductivity Measurements

“…MHPs 1.3 < α < 1.7,[28,29,36,[53][54][55] scattering with acoustic phonons seems to be the dominant factor determining mobility instead of scattering with optical phonons.…”