title: Dominant factors limiting the optical gain in layered two-dimensional halide perovskite thin films.
abstract: Semiconductors are ubiquitous gain media for coherent light sources. Solution-processed three-dimensional (3D) halide perovskites (e.g., CH3NH3PbI3) with their outstanding room temperature optical gain properties are the latest members of this family. Their two-dimensional (2D) layered perovskite counterparts with natural multiple quantum well structures exhibit strong light-matter interactions and intense excitonic luminescence. However, despite such promising traits, there have been no reports on room temperature optical gain in 2D layered perovskites. Herein, we reveal the challenges towards achieving amplified spontaneous emission (ASE) in the archetypal (C6H5C2H4NH3)2PbI4 (or PEPI) system. Temperature-dependent transient spectroscopy uncovers the dominant free exciton trapping and bound biexciton formation pathways that compete effectively with biexcitonic gain. Phenomenological rate equation modeling predicts a large biexciton ASE threshold of ∼1.4 mJ cm(-2), which is beyond the damage threshold of these materials. Importantly, these findings would rationalize the difficulties in achieving optical gain in 2D perovskites and provide new insights and suggestions for overcoming these challenges.
authors.affiliation: Energy Research Institute@NTU, ERI@N, Interdisciplinary Graduate School, Nanyang Technological University, Singapore and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371. Tzechien@ntu.edu.sg.
authors.forename: Wee Kiang
authors.initials: WK
authors.lastname: Chong
authors.affiliation: Energy Research Institute@NTU (ERI@N), Research Techno Plaza, X-Frontier Block, Level 5, 50 Nanyang Drive, Singapore 637553. Subodh@ntu.edu.sg and Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371.
authors.forename: Krishnamoorthy
authors.initials: K
authors.lastname: Thirumal
authors.affiliation: Energy Research Institute@NTU, ERI@N, Interdisciplinary Graduate School, Nanyang Technological University, Singapore and Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371. Tzechien@ntu.edu.sg.
authors.forename: David
authors.initials: D
authors.lastname: Giovanni
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371. Tzechien@ntu.edu.sg.
authors.forename: Teck Wee
authors.initials: TW
authors.lastname: Goh
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371. Tzechien@ntu.edu.sg and CAS Key Laboratory of Standardization and Measurement for Nanotechnology, National Center for Nanoscience and Technology, Beijing 100190, China.
authors.forename: Xinfeng
authors.initials: X
authors.lastname: Liu
authors.affiliation: Energy Research Institute@NTU (ERI@N), Research Techno Plaza, X-Frontier Block, Level 5, 50 Nanyang Drive, Singapore 637553. Subodh@ntu.edu.sg and School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798.
authors.forename: Nripan
authors.initials: N
authors.lastname: Mathews
authors.affiliation: Energy Research Institute@NTU (ERI@N), Research Techno Plaza, X-Frontier Block, Level 5, 50 Nanyang Drive, Singapore 637553. Subodh@ntu.edu.sg and School of Materials Science and Engineering, Nanyang Technological University, Nanyang Avenue, Singapore 639798.
authors.forename: Subodh
authors.initials: S
authors.lastname: Mhaisalkar
authors.affiliation: Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371. Tzechien@ntu.edu.sg.
authors.forename: Tze Chien
authors.initials: TC
authors.lastname: Sum