Chen H.-Y.,TUM CREATE |
Chen H.-Y.,TU Munich |
Chen H.-Y.,Nanyang Technological University |
Chen H.-Y.,National Tsing Hua University |
And 19 more authors.
Physical Chemistry Chemical Physics | Year: 2017
Polyoxometalates (POMs) have been reported as promising electrode materials for energy storage applications due to their ability to undergo fast redox reactions with multiple transferred electrons per polyanion. Here we employ a polyoxovanadate salt, Na6[V10O28], as an electrode material in a lithium-ion containing electrolyte and investigate the electron transfer properties of Na6[V10O28] on long and short timescales. Looking at equilibrated systems, in situ V K-edge X-ray absorption near edge structure (XANES) studies show that all 10 V5+ ions in Na6[V10O28] can be reversibly reduced to V4+ in a potential range of 4-1.75 V vs. Li/Li+. Focusing on the dynamic response of the electrode to potential pulses, the kinetics of Na6[V10O28] electrodes and the dependence of the fundamental electron transfer rate k0 on temperature are investigated. From these measurements we calculate the reorganization energy and compare it with theoretical predictions. The experimentally determined reorganization energy of λ = 184 meV is in line with the theoretical estimate and confirms the hypothesis of small values of λ for POMs due to electrostatic shielding of the redox center from the solvent. © the Owner Societies 2017.
Chong W.K.,Nanyang Technological University |
Thirumal K.,Energy Research InstituteNTU ERIN |
Thirumal K.,Nanyang Technological University |
Giovanni D.,Nanyang Technological University |
And 8 more authors.
Physical Chemistry Chemical Physics | Year: 2016
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. © 2016 the Owner Societies.
Yantara N.,Energy Research Institute@NTU ERI@N |
Bhaumik S.,Energy Research Institute@NTU ERI@N |
Yan F.,Nanyang Technological University |
Sabba D.,Energy Research Institute@NTU ERI@N |
And 7 more authors.
Journal of Physical Chemistry Letters | Year: 2015
Lead-halide perovskites have transcended photovoltaics. Perovskite light-emitting diodes (PeLEDs) emerge as a new field to leverage on these fascinating semiconductors. Here, we report the first use of completely inorganic CsPbBr3 thin films for enhanced light emission through controlled modulation of the trap density by varying the CsBr-PbBr2 precursor concentration. Although pure CsPbBr3 films can be deposited from equimolar CsBr-PbBr2 and CsBr-rich solutions, strikingly narrow emission line (17 nm), accompanied by elongated radiative lifetimes (3.9 ns) and increased photoluminescence quantum yield (16%), was achieved with the latter. This is translated into the enhanced performance of the resulting PeLED devices, with lower turn-on voltage (3 V), narrow electroluminescence spectra (18 nm) and higher electroluminescence intensity (407 Cd/m2) achieved from the CsBr-rich solutions. © 2015 American Chemical Society.
Boxi X.,Nanyang Technological University |
Kumar M.H.,Nanyang Technological University |
Kumar M.H.,Energy Research InstituteNTU ERIN |
Prabhakar R.R.,Energy Research InstituteNTU ERIN |
And 4 more authors.
Nanoscience and Nanotechnology Letters | Year: 2012
Indium Sulfide (In2S3) thin film were deposited on glass substrate through successive ionic layer adsorption and reaction (SILAR) method. The samples were annealed at 250 °C, 350 °C and 450 °C respectively after deposition. The X-ray diffraction (XRD) analysis shows that the sample annealed at 450 °C has the most clear and obvious XRD pattern, which indicates that In2S3 annealed at 450 °C possess the highest crystallinity. Ultraviolet-visible spectroscopy analysis of the samples shows that the band gap of In2S3 is around 2 eV. This study shows that annealing does not induce any change in optical bandgap of In2S3 thin films on glass substrates as reported elsewhere. Copyright © 2012 American Scientific Publishers.