Abstract
Ruddlesden–Popper halide perovskites are 2D solution-processed quantum wells with a general formula A2A’n-1MnX3n+1, where optoelectronic properties can be tuned by varying the perovskite layer thickness (n-value), and have recently emerged as efficient semiconductors with technologically relevant stability. However, fundamental questions concerning the nature of optical resonances (excitons or free carriers) and the exciton reduced mass, and their scaling with quantum well thickness, which are critical for designing efficient optoelectronic devices, remain unresolved. Here, using optical spectroscopy and 60-Tesla magneto-absorption supported by modeling, we unambiguously demonstrate that the optical resonances arise from tightly bound excitons with both exciton reduced masses and binding energies decreasing, respectively, from 0.221 m0 to 0.186 m0 and from 470 meV to 125 meV with increasing thickness from n equals 1 to 5. Based on this study we propose a general scaling law to determine the binding energy of excitons in perovskite quantum wells of any layer thickness.
Highlights
Ruddlesden–Popper halide perovskites are 2D solution-processed quantum wells with a general formula A2A’n-1MnX3n+1, where optoelectronic properties can be tuned by varying the perovskite layer thickness (n-value), and have recently emerged as efficient semiconductors with technologically relevant stability
Ruddlesden–Popper halide perovskites[1,2] (RPPs) are solution-processed quantum well structures formed by two-dimensional (2D) layers of halide perovskite semiconductors separated by bulky organic spacer layers, whose stoichiometric ratios are defined by the general formula[3] A2A’n-1MnX3n+1 where A, A’ are cations, M is a metal, X is a halide and the integer value n determines the perovskite layer thickness
We present the study on using low-temperature (4 K) magneto-optical spectroscopy to accurately determine the exciton reduced mass for (BA)2(MA)n-1PbnI3n+1 RPP crystals with perovskite layer thickness varying between 0.641 and 3.139 nm, corresponding to n varying between 1 and 5 (Fig. 1a, Supplementary Fig. 1, and Supplementary Table 1), where BA and MA stand for CH3(CH2)3NH3 and CH3NH3, respectively
Summary
Ruddlesden–Popper halide perovskites are 2D solution-processed quantum wells with a general formula A2A’n-1MnX3n+1, where optoelectronic properties can be tuned by varying the perovskite layer thickness (n-value), and have recently emerged as efficient semiconductors with technologically relevant stability. The reduced mass of the exciton ground state calculated by density functional theory (DFT) for each RPP (with n equals 1 to 4) yields a similar dependence on the n-value as the experimental ones provided the underestimation of the bandgap computation by DFT is taken into account (Supplementary Fig. 5).
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