Impact of Layer Materials, Their Thicknesses, and Their Reflectivities on Emission Color and NVIS Compatibility in...

Organic Light Emitting Diode (OLED) technology is preferred in modern display applications due to its superior efficiency, color quality, and flexibility. It also carries a high potential of applicability in military displays where emission color tuning is required for MIL-STD-3009 Night Vision Imaging Systems (NVISs), as compatibility is critical. Herein, we report the effects of different OLED device layer materials and thicknesses such as the hole injection layer (HIL), hole transport layer (HTL), and electron transport layer (ETL) on the color coordinates, luminance, and efficiency of OLED devices designed for night vision (NVIS) compatibility. In this study, simulation tools like SETFOS^® (Semi-conducting Emissive Thin Film Optics Simulator), MATLAB^®, and LightTools^® (Illumination Design Software) were used to verify and validate the luminance, luminance efficiency, and chromaticity coordinates of the proposed NVIS-OLED devices. We modeled the OLED device using SETFOS^®, then the selection of materials for each layer for an optimal electron-hole balance was performed in the same tool. The effective reflectivity of multiple OLED layers was determined in MATLAB^® in addition to an optimal device efficiency calculation in SETFOS^®. The optical validation of output luminance and luminous efficiency was performed in LightTools^®. Through a series of simulations for a green-emitting OLED device, we observed significant shifts in color coordinates, particularly towards the yellow spectrum, when the ETL materials and their thicknesses varied between 1 nm and 200 nm, whereas a change in the thickness of the HIL and HTL materials had a negligible impact on the color coordinates. While the critical role of ETL in color tuning and the emission characteristics of OLEDs is highlighted, our results also suggested a degree of flexibility in material selection for the HIL and HTL, as they minimally affected the color coordinates of emission. We validated via a combination of SETFOS^®, MATLAB^®, and LightTools^® that when the ETL (3TPYMB) material thickness is optimized to 51 nm, the cathode reflectivity via the ETL-EIL stack became the minimum enabling output luminance of 3470 cd/m2 through our emissive layer within the Glass/ITO/MoO₃/TAPC/(CBP:Ir(ppy)₃)/3TPYMB/LiF/Aluminum OLED stack architecture, also yielding 34.73 cd/A of current efficiency under 10 mA/cm² of current density. We infer that when stack layer thicknesses are optimized with respect to their reflectivity properties, better performances are achieved.