Full-color,multi-state Transmittance-tunable Films Based On Chalcogenide Phase Change Materials

Full-color,multi-level transmittance modulators(FMTM)represent functional films with full color and multi-level modulation of visible-infrared transmittance through thermal or electrical excitation.FMTM have important applications in many fields such as decorative smart windows,laser safety windows,translucent displays,energy conversion device,etc.For example,depositing FMTM on the inner surface of the glass curtain wall of decorative buildings can provide not only specific colors to meet architectural aesthetic requirements,but also multi-level adjustable solar radiation to save energy.So far,researchers have conducted a lot of research on it.However,there still exists following problems:(1)The color of the traditional transmittance-tunable film is monotonous without high saturation.Traditional transmittance-tunable films include tungsten trioxide(WO₃),vanadium dioxide(VO₂)and chalcogenide phase change materials(PCM),etc.These materials generally have the characteristics of multi-state tunable transmittance in the sunlight waveband(300-2500 nm),but not have ideal RGB colors.Therefore,to integrate transmittance modulation with arbitrary colors,it is necessary to use these transmittance-modulated materials to construct special optical cavities(2)The traditional asymmetric Fabry-Perot(F-P)cavity can achieve full-color,but difficult to achieve transmittance-tunable.The asymmetric F-P cavity structure has a selective reflection enhancement effect caused by interference,which is one of the effective methods to obtain structural colors.To have rich colors and arbitrarily modulated transmittance at the same time,the F-P cavity has not only selective reflection enhancement effects,but also the characteristic of multi-state absorption modulation.However,at present,the reflective layer of all asymmetric FP cavities is limited to pure metals such as Ag,Pt,Au,Al,etc.,and cannot achieve the integration of full-color and multi-state transmittance modulation.Herein,we design an asymmetric FP cavity with a pair of high-and low-activation energy chalcogenide phase change materials as the reflective layer(named as“PCM pair”FP cavity),achieving the combination of full color and multi-level transmittance modulation in a thin film.This is attributed to the“PCM pair”having the coupling effect of selective reflection enhancement and gradient absorption that traditional FP cavities do not have.The main research is divided into two aspects:(1)Research on the full-color and multi-state transmittance modulation properties of Sb₂Te₃/Ge Te/ITO(PCM pair=Sb₂Te₃/Ge Te,SGI)films.According to simulations and experiments of SGI films,we prove that the selective reflectivity enhancement is due to light interference effect between the“PCM pair”and bottom ITO with different thicknesses,which realizes full-color modulations.The gradient absorption results from the multi-stage phase change of“PCM pair”from disorder to order,leading to multi-level electron delocalization behavior.This increases carrier absorption and causes additional interface absorption,thus resulting in high-contrast transmittance modulation with four levels.(2)The“PCM pair”microstructure design principles and material map.The screening criteria for high optical contrast are low hybridization and low ionicity,and the criteria for high-activation energy are low vacancy concentration and small average atomic number.Therefore,this research provides the design principles and candidate materials for the“PCM pair”F-P cavity to solve the problem of the difficulty of integrating full-color and transmittance modulation.