Technical Awardscoating. Therefore, when mounted in the entire area of a car windshield, there was an issue of blocking the driverʼs view in the screen state.Optical switching of liquid crystals (LCs) doped with chiral azobenzene compounds were proposed as an alternative to electrical switching [7, 8]. It was considered to possess high transparency, flexibility, and screen area control. A compensated and transparent nematic phase LC was formed by mixing a chiral azobenzene with a non-photochromic chiral compound having opposite chirality in the host nematic LC by balancing the helical twisting powers (HTPs) of both chiral compounds. The HTP of the chiral azobenzene compounds was decreased using ultraviolet (UV) irradiation to induce their trans-cis photoisomerization and consequently transform the compensated nematic LC into a cholesteric phase. Resultantly, the optically switching LC film changed from its transparent state to light scattering screen state. The transmittance was restored using visible light (Vis) irradiation. As the difference in HTP (ΔHTP) between the trans and cis states of the chiral azobenzene increased, the specular transmittance changed significantly. However, reflectance has not been investigated. In this paper, we describe the improvement of the optical performance of optically switchable reverse-mode PNLCs by increasing the ΔHTP of azobenzene and present a front-projection transparent LCD.Fig. 1 depicts the system layout of the optically switchable transparent LCD. It is composed of an optically switchable reverse-mode PNLC, a Vis projector, 2. Principle of optical switching in transparent LCD2.1 System set-up*Advanced Materials and Processing LaboratoryAbstract We demonstrated a new transparent display consisting of an optically switchable polymer network liquid crystal and light sources. Optical switching between transparent and screen states was achieved through trans-cis photoisomerization of azobenzene. Furthermore, we improved screen reflectance by increasing the helical twisting power difference between the trans and cis states.Recently, transparent displays have been actively developed for applications in signage windows of stores and automotive windows. Transparent displays are required to meet demands such as large sizes, good flexibility, high transparency, cost-effectiveness, and high contrast. Organic light-emitting diode (OLED) displays [1] are a type of transparent display. OLED displays can be large and offer advantages in terms of image quality, such as a large viewing angle, superior color gamut, and high resolution. However, OLED transmittance is low due to the several thin-film transistors (TFTs) and capacitors in each pixel. Transparent liquid crystal displays (LCDs) are another type of transparent display. Polymer-dispersed liquid crystal (PDLC) displays with TFTs [2, 3] can achieve a high transmittance of > 80% in the transparent state, on account of the high aperture ratio of each pixel. When flexible displays with TFTs, such as OLED displays and LCDs, are mounted on a curved surface, such as automotive windows, they are required to be flexible. Transparent polyimide (PI) films are typically used to fabricate TFTs on the substrate surfaces. To date, the demand for transparent PI films is limited only to high-end optoelectronic products, and they are not economical [4].However, transparent PDLC and polymer-network liquid (PNLC) displays using affordable polyethylene terephthalate (PET) films coated with indium tin oxide (ITO) are commercially available. A transparent display using the combination of a projector with PDLCs or PNLCs was proposed [5, 6]. However, the area to be controlled from transparent to screen state by applying voltage was limited, depending on the ITO crystal Technical Awards：The 28th International Display Workshops(IDW) Best Paper Award (2021）1. Introduction99Optically Switchable Transparent Liquid Crystal DisplayYoshimi Ohta* Shunta Nabetani* Maki Kamikubo*Tomoya Ohara* Ryota Maehashi* Fuminori Sato*
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