Bandgap-universal passivation enables stable perovskite solar cells with low photovoltage loss

The efficiency and longevity of metal-halide perovskite solar cells are typically dictated by nonradiative defect-mediated charge recombination. In this work, we demonstrate a vapor-based amino-silane passivation that reduces photovoltage deficits to around 100 millivolts (>90% of the thermodynamic limit) in perovskite solar cells of bandgaps between 1.6 and 1.8 electron volts, which is crucial for tandem applications. A primary-, secondary-, or tertiary-amino–silane alone negatively or barely affected perovskite crystallinity and charge transport, but amino-silanes that incorporate primary and secondary amines yield up to a 60-fold increase in photoluminescence quantum yield and preserve long-range conduction. Amino-silane–treated devices retained 95% power conversion efficiency for more than 1500 hours under full-spectrum sunlight at 85°C and open-circuit conditions in ambient air with a relative humidity of 50 to 60%

Bistable twisted nematic liquid crystal display using photoalignment technology

Bistable twisted nematic (BTN) liquid crystal displays (LCDs) traditionally have bistable twisted states that differ in twist angle by 2π. Unfortunately, these 2π-BTN displays have an intermediate twist state in π which is more stable than the two metastable states 0 and 2π. So, the 2π-BTN has not been useful. Recently, different researches on π-BTN have been conducted. In this thesis, truly bistable twisted nematic liquid crystal display has been fabricated using photoalignment technology. This display can be switched between the -22.5° and 157.5° twist state by breaking of the anchoring on one of the substrates. The application of a photoalignable polymer SDA-1 was able to achieve the weak anchoring condition necessary for switching. Both theoretical and experimental results show that this mode has excellent contrast ratio and wide viewing angles

Variable liquid crystal pretilt angles by nanostructured surfaces and their applications

Liquid crystal displays (LCDs) are conventionally aligned by rubbing of a polyimide (PI) layer. Pretilt angles of 0°–10° are usually obtained for homogeneous alignment polyimide. Vertical alignment polyimide can give a pretilt angle of 85°–90°. However, there is much demand for an alignment layer that can produce intermediate high pretilt angles in the range of 30°–60°. Many applications can be made possible if such large pretilt angles are available. Traditionally, the best method of obtaining large pretilt angles is by SiO2 evaporation. However, this technique is not amenable to mass production and for large display panels. There have been other proposed methods including photoalignment technology, special polymer blends and block copolymers as the alignment layer. But none of them has proven useful so far. We have recently described a nanostructured alignment surface based on a random distribution of vertical and horizontal polyimide domains. In this thesis, we report results on these nanostructured surfaces to prove their usefulness in making novel liquid crystal displays. In particular, as the alignment layer for LCD, we show that such surfaces can indeed provide any pretilt angles between 0° and 90°. The polar anchoring energy of such surfaces is also very strong, being comparable to ordinary rubbed polyimides. In fact, ordinary polyimides are employed as the main ingredient in making such nanostructured surfaces. With these alignment layers, no-bias voltage π cells and several bistable displays have been successfully fabricated

22.2 / F. S.-Y. Yeung 22.2: Photoaligned Transmissive Bistable TN-LCD

Transmissive bistable twisted nematic liquid crystal display has been fabricated using photoalignment. This display can be switched by breaking of the anchoring on one of the substrates. The application of a new photo-alignable polymer SDA-1 was able to achieve the weak polar anchoring condition necessary for switching. 1

Bistable twisted nematic liquid crystal display based on dual frequency operation

The invention provides a bistable twisted nematic liquid crystal display, comprising a first substrate having thereon a first conductive layer and a first alignment layer; a second substrate having thereon a second conductive layer and a second alignment layer; a liquid crystal layer in the first and second alignment layers; an alignment layer on each of the substrates, the alignment layer imparting a preferred direction for liquid crystal molecules near the alignment layer, and possessing different azimuthal and polar anchoring energies when used to align a liquid crystal layer: the alignment layers being rubbed in such a way to give a stable twist angle of the liquid crystal of Φ where Φ can be any value in between -45° to +45°; and wherein the d/p radio of the liquid crystal layer is between the values of 0.15+0.5Φ/Ï and 0.35+0.5Φ/Ï

62.2 / F. S.-Y. Yeung 62.2: Dual-Frequency Bistable Bend-Splay LCDs

A bistable liquid crystal display based on the bend and splay configurations has been demonstrated using dual frequency liquid crystal. Unlike the previous three-electrode version, only two regular electrodes are needed in the present case. We also propose and demonstrate a convenient multiplex driving scheme for a BBS matrix display. 1

Enhancing Pixel Charging Efficiency by Optimizing Thin-Film Transistor Dimensions in Gate Driver Circuits for Active-Matrix Liquid Crystal Displays

Flat panel displays are electronic displays that are thin and lightweight, making them ideal for use in a wide range of applications, from televisions and computer monitors to mobile devices and digital signage. The Thin-Film Transistor (TFT) layer is responsible for controlling the amount of light that passes through each pixel and is located behind the liquid crystal layer, enabling precise image control and high-quality display. As one of the important parameters to evaluate the display performance, the faster response time provides more frames in a second, which benefits many high-end applications, such as applications for playing games and watching movies. To further improve the response time, the single-pixel charging efficiency is investigated in this paper by optimizing the TFT dimensions in gate driver circuits in active-matrix liquid crystal displays. The accurate circuit simulation model is developed to minimize the signal’s fall time (Tf) by optimizing the TFT width-to-length ratio. Our results show that using a driving TFT width of 6790 μm and a reset TFT width of 640 μm resulted in a minimum Tf of 2.6572 μs, corresponding to a maximum pixel charging ratio of 90.61275%. These findings demonstrate the effectiveness of our optimization strategy in enhancing pixel charging efficiency and improving display performance

A liquid crystal alignment layer and methods of making thereof

The present invention relates to a liquid crystal alignment layer used in a liquid crystal cell, which is capable of providing high pretilt angles

P-11 / X. Li Abstract P-11: LC Display Cell Photo-alignment by a Super-thin Azo-dye Layer

We proposed a novel method of forming a super-thin azo-dye molecular alignment layer for LC display cell without spincoating and rubbing processes. The high electrooptical performance of photo-aligned LC cells was demonstrated in ECB and TN modes. Providing the advantages of conventional photoalignment methods, the use of super thin layer simplifies the alignment procedure, makes possible high contrast ratio and better adhesion on ITO rough surface. 1