ABX.SUB.3 .perovskite particles and their application in reverse mode controlling photo-flux

Abstract

A reverse mode light valve, the manufacture of a light control device and a method of controlling light transmittance by using of the reverse mode light valve, the reverse mode light valve containing ABX.sub.3 perovskite particles (200) suspended in a liquid suspension (300) can control light transmittance in a higher light transmittance when the power is turned off (OFF state) and lower light transmittance when the power is turned on (ON state). In the ABX.sub.3 perovskite particles (200), A is at least one of Cs.sup.+, CH.sub.3NH.sub.3.sup.+, and Rb.sup.+, B is at least one of Pb.sup.2+, Ge.sup.2+, and Sn.sup.2+, and X is at least one of Cl.sup.−, Br.sup.−, and I.sup.−.

Claims

1. A light valve, comprising a first layer of a transparent conductive substrate; an active layer containing ABX.sub.3 perovskite particles suspended in a liquid suspension; and a second layer of a transparent conductive substrate, wherein A is at least one of Cs.sup.+ and CH.sub.3NH.sub.3.sup.+, B is Pb.sup.2+, and X is at least one of Bf and I.sup.−; and the ABX.sub.3 perovskite particles have a morphology of nanosheets having a length of 200 nm-500 nm, a thickness of 10 nm 50 nm, a width of 200 nm 500 nm, and a ratio of width: thickness above 3:1, wherein the light valve has a higher light transmittance on OFF-state and a lower light transmittance on ON-state.

2. The light valve as recited in claim 1, wherein the perovskite particles are uniformly dispersed in the liquid suspension.

3. The light valve as recited in claim 2, wherein the liquid suspension is capable of maintaining the suspended ABX.sub.3 perovskite particles in gravitational equilibrium.

4. The light valve as recited in claim 2, wherein the liquid suspension comprises one or more of a mineral resistive material, a synthetic resistive material, a vegetable oil.

5. The light valve as recited in claim 2, wherein the liquid suspension is sandwiched between the first layer of a transparent conductive substrate and the second layer of a transparent conductive substrate as transparent electrodes.

6. A method of controlling light transmittance, comprising using the light valve according to claim 1 in a light control device.

7. A method of manufacturing a light control device, comprising using the light valve according to claim 1.

8. The method according to claim 7, wherein the light control device is selected from the group consisting of a smart window, a rear window of a car, a lens, a light shutter and a display.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 presents schematically the r-LV, wherein, a liquid suspension (300) is sandwiched between two transparent substrates (100) and (100). The ABX.sub.3 perovskite particles (200) are suspended in the liquid suspension (300).

(2) FIG. 2 presents light transmittance of a r-LV device made according to this invention Example 6 before and after applying an electric voltage of 220V.

(3) FIG. 3 presents SEM image of CsPbBr.sub.3 nanosheets according to this invention Example 3.

(4) FIG. 4 presents the cell structure of the ABX.sub.3 perovskite.

DETAILED DESCRIPTION

(5) The present invention provides a new use for ABX.sub.3 perovskite particles to control the flux of light in a light control device in a reverse mode, thus referred as a reverse light valve (r-LV).

(6) FIG. 1 schematically illustrates a typical r-LV device, wherein, a liquid suspension (300) is sandwiched between two transparent substrates (100) and (100). The ABX.sub.3 perovskite particles (200) are suspended in the liquid suspension (300). Without any theory limitation, it is assumed that, in the absence of an applied electrical field (OFF state), the ABX.sub.3 perovskite particles in the liquid suspension assume random positions due to Brownian movement. Hence, the beam of light passing into the light valve is partially absorbed/scattered, other part of light transmits through the light valve, so the light valve is thus relatively bright and transparent in the OFF state. When an electric field is applied thereto (ON state), the light control ABX.sub.3 perovskite particles are polarized, that the effective maximum surface of the ABX.sub.3 perovskite particles is perpendicular to the direction of the electric field. Hence, a major part of light going into the light valve is absorbed/scattered, and other smaller fraction of light is transmitted through, so the light valve is thus relatively darker and less transparent in the ON state.

(7) Therefore, being the first time, the present invention provides a novel use of the ABX.sub.3 perovskite particles in a reverse mode light control device (r-LV). According to the present invention, the invented r-LV comprises a liquid suspension having such a material of ABX.sub.3 perovskite particles, which can electronically control transmission of light in such way that it allows more light transmitted through when the power is turned off (OFF state) and less light transmitted through when the power is turned on (ON state). Still, ABX.sub.3 perovskite particles with a more specific chemical composition is disclosed, where A is at least one of Cs.sup.+, CH.sub.3NH.sub.3.sup.+, and Rb.sup.+, B is at least one of Pb.sup.2+, Ge.sup.2+, and Sn.sup.2+, and X is at least one of halide anions selected from Cl.sup.−, Br.sup.−, or I.sup.−. Accordingly, the specified ABX.sub.3 perovskite material is also referred to as halide ABX.sub.3 perovskite material. According to this invention, the ABX.sub.3 perovskite material is used in a form of particles, thus more specifically these particles used can also be referred to as halide ABX.sub.3 perovskite particles. Still according to the invention, these ABX.sub.3 perovskite particles are characterized in that have a non-spherical morphology. Still further, the ABX.sub.3 perovskite particles morphology is at least one of nanorods (one-dimensional); nanosheets (two-dimensional); cuboids, and irregular (three-dimensional). In particularly preferred embodiments, the ABX.sub.3 perovskite particles have a morphology of nanosheets.

(8) As illustrated in FIG. 1, the ABX.sub.3 perovskite particles (200) which are encapsulated inside the said liquid suspension (300) are preferably capable of re-orientating themselves in an electronic field. Therefore, the geometric dimension of the ABX.sub.3 perovskite particles are preferably scientifically optimized. According to the invention, the ABX.sub.3 perovskite particles are preferably in a form of flakes and also referred to as nanosheets herein. Still the nanosheets are preferably having a length of about 50 nm-2000 nm, more preferably 200 nm-500 nm, and a thickness of 5 nm-100 nm, more preferably 10 nm-50 nm.

(9) More preferably, for the nanosheets, it has a length of 50 nm-2000 nm, more preferable 200 nm-500 nm, and a thickness of 5 nm-100 nm, more preferable 10 nm-50 nm, and a width of 50 nm-2000 nm, more preferable 200 nm-500 nm. More preferably, for the nanosheets, it has a ratio of width:thickness of 1:1, more preferable a ratio of width:thickness above 3:1. Particularly preferably, for the nanosheets, it has a length of 200 nm-500 nm, a thickness of 10 nm-50 nm, a width of 200 nm-500 nm, and a ratio of width:thickness above 3:1.

(10) According to the invention, the ABX.sub.3 perovskite particles are preferably capable of being polarized under an electric field, and still the effective maximum surface of the polarized ABX.sub.3 perovskite particles is perpendicular to direction of the electric field. In one embedment, the ABX.sub.3 perovskite particles are nanosheets, after being polarized under an electric field, the surface of the large specific surface of the nanosheets is oriented to be perpendicular to the direction of the electric field.

(11) According to this invention, the liquid suspension (300), which is used as a liquid medium to suspend the ABX.sub.3 perovskite particles, comprises one or more non-aqueous, electrically resistive liquids or a liquid mixture. Such a liquid or a liquid mixture, referring as the suspension medium, can maintain the suspended ABX.sub.3 perovskite particles in gravitational equilibrium.

(12) The liquid suspension medium used in the reverse mode light valve of the present invention can be any proper liquid suspension medium known in the art and can be formulated according to techniques well known to those skilled in the art. Preferably, the liquid suspension (300) comprises one or more suspension medium selected from the group consisting of a mineral resistive material, a synthetic resistive material, and a vegetable oil. Mineral resistive materials, such as transformer oils; synthetic resistive materials, such as silicone oils, fluorocarbon organic compounds, plasticizers (such as Dioctyl phthalate, Dibutyl phthalate, Diisobutyl phthalate, Triisodecyl trimellitate (TDTM) etc.), dodecylbenzene, polybutene oil, etc.; vegetable oils, such as castor oil, soybean oil, rapeseed oil, etc., are good liquid suspension mediums.

(13) According to this invention as illustrated in FIG. 1, the transparent electrodes (100) at both sides can be made of the same material or different materials, where light can be transmitted through, preferably having a light transmittance equals to or greater than 80%, more preferably 90%. Either one or both the transparent electrodes (100) can be ITO conductive glass, ITO/PET conductive film, Ag nanowire/PET conductive film, or Cu nanowire/PET conductive film. The transparent electrodes (100) are preferred to be of the same material for the simplicity of processing and for the same physical properties (such as flexibility and thermal expansion), important for device durability under certain conditions, such as thermal stress.

(14) The liquid suspension containing the ABX.sub.3 perovskite particles sandwiched between the two transparent electrodes is preferably sealed with a resistive material, such as epoxy resin, etc. An alternating current is preferably applied through the transparent electrodes (110) to control the light transmittance through the assembled r-LV, and the voltage of such an alternating current is preferably in the range of 5-500 V, more preferably in a range of 30-220 V, which can be easily achieved by a common transformer.

(15) The invention will now be described in more detail with reference to the following examples. However, these examples are given for illustration only and are not intended to limit the scope of the present invention. All chemicals used in the examples are purchased from Sigma-Aldrich Company unless otherwise specified. In all these examples, all parts and percentages are by weight unless otherwise noted. The light transmittance and absorption spectrum of the r-LV device was measured by an Oceanview spectrometer.

Example 1 Preparation of Cs-Oleate

(16) Cesium carbonate (Cs.sub.2CO.sub.3, 4.07 g) was loaded into a 250 mL 3-neck flask along with octadecene (ODE, 50 mL) and oleic acid (11.088 g), and the mixture was dried for 1 h at 120° C. and then heated under Argon (Ar) to 150° C. until all Cs.sub.2CO.sub.3 reacted with oleic acid. The obtained Cs-Oleate may precipitate out of ODE at room temperature, and it can be preheated to make it soluble before further using.

Example 2 Synthesis of CsPbI.SUB.3 .Nanosheets

(17) N, N-dimethylformamide (DMF, 100 mL) and lead iodide (PbI.sub.2, 2.305 g) were charged into a 250 mL flask. Oleic acid (0.438 g) and octylamine (2.339 g) were added. After complete solubilization of PbI.sub.2, 5 mL Cs-Oleate solution was added (prepared as described in Example 1). Then, the resulted solution was added into a 5 L flask along with 4200 mL of toluene. Subsequently, the resulted solution was centrifuged at 5000 G for 1.5 hours and the supernatant was discarded to yield the light control CsPbI.sub.3 nanosheets. Finally, the CsPbI.sub.3 nanosheets were further dispersed with 500 mL of toluene, mixed well with shaking and sonication (referring to as LCP-Example-2).

Example 3 Synthesis of CsPbBr.SUB.3 .Nanosheets

(18) In the same manner as in Example 2, except that 1.835 g of PbBr.sub.2 was used instead of 2.305 g of PbI.sub.2. A toluene mixture containing CsPbBr.sub.3 nanosheets is obtained and referred to as LCP-Example-3. FIG. 3 presents SEM image of CsPbBr.sub.3 nanosheets.

Example 4 Preparation of r-LV Suspension Containing CsPbI.SUB.3 .Nanosheets

(19) Into a 250 mL round bottom glass flask was weighted 10 g of Triisodecyltrimellitate (TDTM), then the LCP-Example-2 prepared in the Example 2 was added in portions. After thoroughly mixing the resulted suspension by shaking, toluene was subsequently removed by a rotary evaporator for 3 hours at 80° C. to yield a r-LV suspension containing CsPbI.sub.3 nanosheets, which is referred to as r-LV Suspension Example-4.

Example 5 Preparation of r-LV Suspension Containing CsPbBr.SUB.3 .Nanosheets

(20) Into a 25 0 mL round bottom glass flask was weighted 10 g of silicone oil, then the LCP-Example-3 prepared in the Example 3 was added in portions. After thoroughly mixing the resulted suspension by shaking, toluene was subsequently removed by a rotary evaporator for 3 hours at 80° C. to yield a r-LV suspension containing CsPbBr.sub.3 nanosheets, which is referred to as r-LV Suspension Example-5.

Example 6 r-LV Devices Made from r-LV Suspension-Example-4

(21) In this example, a layer of the r-LV Suspension-Example 4 made in Example 4 at a thickness of 200 um was sealed between two transparent electrodes of ITO conductive glass using epoxy resin to produce a light valve referring as r-LV Device-6. When no electric voltage was applied (OFF State), r-LV Device-6 exhibited an orange tint and light transmission was measured to be 19.4%. When it was electrically activated using 220 Volts AC at 50 Hz (ON State), the r-LV Device-6 became darker and light transmission was measured to be 7.0% only. Table 1 summarizes these results. Further, FIG. 2 presents the absorption spectrum of r-LV Device-6 at OFF state and ON state respectively.

Example 7 r-LV Devices Made from r-LV Suspension-Example-5

(22) In this example, a layer of the r-LV Suspension-Example 5 made in Example 5 at a thickness of 180 μm was sealed between two transparent electrodes of ITO conductive glass using epoxy resin to produce a light valve referring to as r-LV Device-7. When no electric voltage was applied (OFF State), r-LV Device-7 exhibited an orange tint and light transmission was measured to be 25.1%. When it was electrically activated using 220 Volts AC at 50 Hz (ON State), the r-LV Device-7 became darker and light transmission was measured to be 12.5% only as listed in Table 1.

(23) TABLE-US-00001 TABLE 1 Typical performance of r-LV devices Transmittance % Example r-LV Device Off state On state Example 6 r-LV Device-6 19.4  7.0 Example 7 r-LV Device-7 25.1 12.5