Correlating the morphology of emitter layer in perovskite based LED to its opto-electronic properties

• Main Author: Anson
• Other Authors: Nripan Mathews
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering::Materials::Photonics and optoelectronics materials
• Online Access: http://hdl.handle.net/10356/66453
• Institution: Nanyang Technological University

The use of organic/inorganic perovskite as the emission layer in optoelectronic application has attracted enormous interest due to combination of superior properties in inorganic materials (such as carrier diffusion length [1-3], high photoluminescence quantum efficiency[4]) and organic materials (such as tunable bandgap[5] , low defect densities[6] and low temperature solution processability[7]). Particularly in light-emitting application, there have been rapid developments in the recent years following the breakthrough where bright electroluminescence (364 cd.m-2 ) was reported to be achieved at room temperature through methylammonium lead halide (CH3NH3PbX3, X = I, Cl, Br) emission layer based lightemitting diode (LED) [8]. Many efforts have since been done to improve the performance, such as improvement on hole injection efficiency[9, 10] and perovskite layer uniformity[11-13] . Most recently, a remarkable maximum luminance (10590 cd.m-2 ) and external quantum efficiency (EQE) (0.48%) was demonstrated through the optimization in film uniformity[12] . This suggested the close connection between perovskite morphology and the performance of device. In this project, the correlation between CH3NH3PbBr3 morphology (particle size, thickness, and film coverage) and its opto-electronic properties has been investigated. Five different morphologies which were produced through different deposition conditions (variation in P123 surfactant (triblock poly(ethylene glycol)[PEG] - poly(propylene glycol)[PPG]-poly(ethylene glycol)[PEG]), CH3NH3PbBr3 concentration, toluene proportion, and anti-solvent (toluene) wash) has been characterized for their optical properties and electrical (device) performance. Optically, the samples with higher film coverage have shown significant increase in their absorption and emission intensity. This is attributable to the increase in CH3NH3PbBr3 active volume which participated in the optical activity. The device test has also shown improvement in CH3NH3PbBr3 electroluminescence performance due to lower defect (trap) sites and less electrical shunting loss, which is associated with bigger particles, higher film coverage and sufficient thickness. On the whole, morphological control of CH3NH3PbBr3 has been shown to result in considerable improvement in its opto-electronic properties. This finding provides insights for further improvement in the performance of perovskite based LED devices.