Overcoming the electroluminescence efficiency limitations of perovskite light-emitting diodes.

Organic-inorganic hybrid perovskites are emerging low-cost emitters with very high color purity, but their low luminescent efficiency is a critical drawback. We boosted the current efficiency (CE) of perovskite light-emitting diodes with a simple bilayer structure to 42.9 candela per ampere, similar to the CE of phosphorescent organic light-emitting diodes, with two modifications: We prevented the formation of metallic lead (Pb) atoms that cause strong exciton quenching through a small increase in methylammonium bromide (MABr) molar proportion, and we spatially confined the exciton in uniform MAPbBr3 nanograins (average diameter = 99.7 nanometers) formed by a nanocrystal pinning process and concomitant reduction of exciton diffusion length to 67 nanometers. These changes caused substantial increases in steady-state photoluminescence intensity and efficiency of MAPbBr3 nanograin layers.This work was partially supported by Samsung Research Funding Center of Samsung Electronics under Project Number SRFC-MA-1402-07. A.S. was partially supported by the Engineering and Physical Sciences Research Council (UK).This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by the American Association for the Advancement of Science

Effects of Virtual Reality-Based Graded Exposure Therapy on PTSD Symptoms: A Systematic Review and Meta-Analysis

Previous studies reported that virtual reality (VR)-based exposure therapy (VRET) was a clinically beneficial intervention for specific phobias. However, among VRET, VR-based graded exposure therapy (VR-GET) is little known about its efficacy on posttraumatic stress disorder (PTSD) symptoms. Therefore, this meta-analysis investigated the effects of VR-GET for PTSD symptoms. A literature search yielded seven randomized controlled trials. The differences between conditions regarding the primary outcome of PTSD symptoms in the effect size of the individual study were calculated using Hedges’ g. The findings showed VR-GET showed a significantly larger effect size for PTSD symptoms (g = 1.100, p = 0.001), compared to controls. However, no significant difference between conventional VRET and controls was found for PTSD symptoms (g = −0.279, p = 0.970). These findings indicated the superiority of VR-GET for PTSD symptoms compared to controls, supporting the importance of immersive PTSD treatments. Nevertheless, the results need to be interpreted with caution due to the substantial number of military service personnel studies. Future trials, considering individually tailored scenarios in virtual environments to cover a wider range of trauma types, are required to investigate its evidence on treating PTSD

Mixed Cations Enabled Combined Bulk and Interfacial Passivation for Efficient and Stable Perovskite Solar Cells

Highlights A mixed GAI and MAI (MGM) treatment modulating the bulk and interfacial defects simultaneously is reported. The devices’ performance is enhanced to ~24.5% in 0.12 cm2 and ~18.7% in 64 cm2 with improved stability. The MGM treatment can be applied to a wide range of perovskite compositions

Chemical Management for Colorful, Efficient, and Stable Inorganic-Organic Hybrid Nanostructured Solar Cells

Chemically tuned inorganic-organic hybrid materials, based on CH3NH3(=MA)Pb(I1-xBrx)(3) perovskites, have been studied using UV-vis absorption and X-ray diffraction patterns and applied to nanostructured solar cells. The band gap engineering brought about by the chemical management of MAPb(I1-xBrx)(3) perovskites can be controllably tuned to cover almost the entire visible spectrum, enabling the realization of colorful solar cells. We demonstrate highly efficient solar cells exhibiting 12.3% in a power conversion efficiency of under standard AM 1.5, for the most efficient device, as a result of tunable composition for the light harvester in conjunction with a mesoporous TiO2 film and a hole conducting polymer. We believe that the works highlighted in this paper represent one step toward the realization of low-cost, high-efficiency, and long-term stability with colorful solar cellsclose58

Improvement of nonlinear response for the power conversion efficiency with light intensities in cobalt complex electrolyte system

A vertically aligned TiO2 photoelectrode with sufficient space between TiO2 nanorods was synthesized by sacrificial templating of ZnO nanorods grown on a dense TiO2 layer/FTO film. The more expanded pore space in the TiO2 nanorod film than conventional mesoscopic TiO2 film greatly reduces the mass transport problem of cobalt electrolyte in the vicinity of the Sb2S3 sensitizer in Sb2S3-sensitized photoelectrochemical solar cells. Therefore, the nonlinearity of the power conversion efficiency (PCE) under illumination intensity was greatly relieved to 5.0% (0.1 sun), 4.7% (0.5 sun), and 3.7% (1 sun) in a TiO(2-)nanorod-based Sb2S3-sensitized solar cell, whereas the efficiency of a mesoscopic-TiO2-based solar cell was significantly degraded to 5.3% (0.1 sun), 3.8% (0.5 sun), and 2.3% (1 sun). (C) 2013 Elsevier B.V. All rights reservedclose

A discussion on the origin and solutions of hysteresis in perovskite hybrid solar cells

Although the record efficiencies of perovskite hybrid solar cells are gradually reaching the efficiency of crystalline Si solar cells, perovskite hybrid solar cells often exhibit significant current density-voltage (J-V) hysteresis with respect to the forward and reverse scan direction and scan rate. The origin of the J-V hysteresis of perovskite hybrid solar cells has not, to date, been clearly elucidated. Dielectric polarization by the ferroelectric properties of perovskite (i), the ionic motion/migration of perovskite materials (ii), and charge trapping and detrapping at trap sites by the unbalanced electron and hole flux (iii) are considered the possible origins of J-V hysteresis. Here, we reviewed the origin of the J-V hysteresis of perovskite solar cells from the above three points of view and we then suggest how one may reduce the J-V hysteresis with respect to the scan direction and scan rate.

Efficient hysteresis-less bilayer type CH3NH3PbI3 perovskite hybrid solar cells

Bilayer type CH3NH3PbI3 (MAPbI3) perovskite hybrid solar cells were fabricated via a one-step spin-coating process by using solubility controlled MAPbI3 solutions of MAPbI3-DMSO (dimethyl sulfoxide) and MAPbI3-DMF (N, N-dimethylformamide)-HI. The best DMSO-bilayer device showed 1.07 ±0.02 V V oc (open-circuit voltage), 20.2 ±0.1 mA cm-2 J sc (short-circuit current density), 68 ±2% FF (fill factor), and 15.2 ±0.3% η (overall power conversion efficiency) under the forward scan direction and 1.07 ±0.02 V V oc, 20.4 ±0.1 mA cm-2 J sc, 70 ±3% FF, and 15.9 ±0.4% η under the reverse scan direction. The best HI-bilayer device had 1.08 ±0.02 V V oc, 20.6 ±0.1 mA cm-2 J sc, 75 ±1% FF, and 17.2 ±0.2% η under the forward scan direction and 1.08 ±0.02 V V oc, 20.6 ±0.1 mA cm-2 J sc, 76 ±2% FF, and 17.4 ±0.3% η under the reverse scan direction. The deviation of average device efficiency ( of 20 DMSO samples and 20 HI samples was 14.2 ±0.95% and 16.2 ±0.85%, respectively. Therefore, the HI-bilayer devices exhibited better device efficiency and smaller J-V (current density-voltage) hysteresis with respect to the scan direction than the DMSO-bilayer devices due to the reduced recombination and traps by the formation of a purer and larger MAPbI3 perovskite crystalline film. © 2016 IOP Publishing Ltd.

Three-Dimensional Structures Based on the Fusion of Chrysene and Spirobifluorene Chromophores for the Development of Blue OLEDs

A new deep-blue chromophore containing a three-dimensionally (3D) shaped CS core composed of fused chrysene and spirofluorene units is synthesized. A pair of <i>m</i>-terphenyl (TP) units is also substituted onto the CS core at two different sets of positions to form two additional compounds: CS–TPTP and TP–CS–TP. The TP–CS–TP compound showed the highest efficiency with an external quantum efficiency (EQE) of 3.05% and Commission Internationale de L’Eclairage coordinates (CIE) of (0.148, 0.098) corresponding to the emission of blue light. This approach for forming a new chromophore is expected to lead to the development of functional organic materials with excellent characteristics

Three-Dimensional Structures Based on the Fusion of Chrysene and Spirobifluorene Chromophores for the Development of Blue OLEDs

A new deep-blue chromophore containing a three-dimensionally (3D) shaped CS core composed of fused chrysene and spirofluorene units is synthesized. A pair of <i>m</i>-terphenyl (TP) units is also substituted onto the CS core at two different sets of positions to form two additional compounds: CS–TPTP and TP–CS–TP. The TP–CS–TP compound showed the highest efficiency with an external quantum efficiency (EQE) of 3.05% and Commission Internationale de L’Eclairage coordinates (CIE) of (0.148, 0.098) corresponding to the emission of blue light. This approach for forming a new chromophore is expected to lead to the development of functional organic materials with excellent characteristics