Self-trapped excitons in two-dimensional perovskites
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REVIEW ARTICLE
Self-trapped excitons in two-dimensional perovskites Junze LI1, Haizhen WANG (✉)1, Dehui LI (✉)1,2 1 School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074, China 2 Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China
© Higher Education Press 2020
Abstract With strong electron–phonon coupling, the self-trapped excitons are usually formed in materials, which leads to the local lattice distortion and localized excitons. The self-trapping strongly depends on the dimensionality of the materials. In the three-dimensional case, there is a potential barrier for self-trapping, whereas no such barrier is present for quasi-one-dimensional systems. Two-dimensional (2D) systems are marginal cases with a much lower potential barrier or nonexistent potential barrier for the self-trapping, leading to the easier formation of self-trapped states. Self-trapped excitons emission exhibits a broadband emission with a large Stokes shift below the bandgap. 2D perovskites are a class of layered structure material with unique optical properties and would find potential promising optoelectronic. In particular, self-trapped excitons are present in 2D perovskites and can significantly influence the optical and electrical properties of 2D perovskites due to the soft characteristic and strong electron–phonon interaction. Here, we summarized the luminescence characteristics, origins, and characterizations of self-trapped excitons in 2D perovskites and finally gave an introduction to their applications in optoelectronics. Keywords self-trapped exciton (STE), two-dimensional (2D) perovskites, broadband emission, electron–phonon coupling, optoelectronic applications
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Introduction
Since the rapid development in the field of solar cells, organic–inorganic hybrid perovskite has attracted tremendous interest [1,2]. Recently, the power conversion efficiency of perovskite solar cells has overpassed to 25% [3]. Nevertheless, although great progress has been Received May 26, 2020; accepted July 8, 2020 E-mails: [email protected] (H. Wang), [email protected] (D. Li)
made in the perovskite-based solar cells, the stability of perovskites in ambient prevents perovskite solar cells from being commercialized [4]. One solution to address the stability issue is the insertion of organic chains between the inorganic octahedral sheets so that the inorganic layers are protected from being contacted by the moisture in the air. Under such a case, the so-called two-dimensional (2D) perovskites are formed with improved stability [5–7]. The 2D perovskites are one class of layered materials, and we can mechanically exfoliate thin flakes from their bulk crystals and further integrate with other layered materials to achieve the desired functionalities [7–10]. Furthermore, the bandgap and electronic band structure can be easily tuned by changing the organic cations or layer number, which provides great flexibility for the optoelectronic applications
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