Among several components that affect the performance of display devices, i.e. LED, optical films, or liquid crystal (LC) cell; quantum dot (QD) based optical films are newly employed constituents of display technologies that... [ view full abstract ]
Among several components that affect the performance of display devices, i.e. LED, optical films, or liquid crystal (LC) cell; quantum dot (QD) based optical films are newly employed constituents of display technologies that aim to replace conventional solid state lighting techniques, e.g. blue-LED-chip-plus-yellow-phosphor combination. Despite their main advantages such as high efficiency, narrow emission band, and spectral tunability, quantum dots suffer from the optical losses due to reabsorption at different concentrations.
In this study, we focus on the computational modelling of green-emitting CdSe/ZnS- and red-emitting CdSe/CdS-based optical films as color convertors to reveal the effects of QD concentrations on the output spectrum. The evaluation of the numerical results is compared in terms of color gamut, luminance and chromaticity coordinates. A Monte Carlo ray-tracing algorithm in MATLAB is developed to simulate the QD based optical sheets (QDs) for smartphone usage at different green and red QD concentration levels, and the output that yields the highest luminous efficiency, the highest color gamut, and chromaticity coordinates best fit to display standards (Cx = 0.285, Cy = 0.293 in CIE 1931 color space) are presented. The results are also confirmed with that of the commercial optical-simulation software LightTools.
We use at least 100000 incident photons onto the QDs to obtain reproducible results. Before the incident photons reach the nanoparticles, they first interact with the boundary of the optical host material of PDMS. The algorithm mainly tracks the movement of every single photon from their first entry to the QD boundaries until their withdrawal. The simulations yield satisfactory results, i.e., 80% DCI Color Gamut in CIE 1976 standards, or chromaticity coordinates (0.288, 0.293), and the spectra of the corresponding QD concentration levels are plotted. It must be noted that these simulations contain only QDs among the optical components that constitutes the backlight unit of a smartphone. Considering the lack of additional films, i.e. diffuser sheet, prism sheet, and reflective polarizer, a Color Gamut value of 80% corresponds to a value close to 100% with the addition of the mentioned optical components.
