All-solid-state spatial light modulator based on perovskite crystal

Abstract

The utility model discloses an all-solid-state spatial light modulator based on perovskite crystals. The all-solid-state spatial light modulator comprises a CMOS array circuit and a perovskite phase modulation layer. The CMOS array circuit is composed of a field effect transistor composed of a source electrode, a drain electrode, a gate electrode, a monocrystalline silicon channel and a dielectric layer, a storage capacitor composed of an upper electrode, a lower electrode and the dielectric layer, a metal connecting layer, a metal shading layer and the like. The perovskite phase modulation layer is composed of a reflection electrode, a perovskite single crystal layer and a transparent electrode. According to the utility model, the phase modulation of the perovskite single crystal layer is combined with the CMOS array circuit, and the spatial light wavefront is modulated through array pixels. The all-solid-state spatial light modulator based on the perovskite crystal provided by the utility model is fast in electro-optical response speed, can adapt to application requirements of high-speed light beam driving, optical communication and the like, is high in sensitivity and low in pi-phase modulation voltage, and can realize regulation and control of two-dimensional wavefront through an array project.

Description

Technical Field

[0001] The utility model relates to the field of light field regulation, in particular to electro-optical modulation technology. Background Art

[0002] A spatial light modulator is a device that can load modulation information into the input light field. It can change the parameters such as the amplitude, phase and polarization state of the spatial light field under the drive of time-varying electrical signals or other signals. There are many types of spatial light modulators, such as liquid crystal spatial light modulators, deformable mirror spatial light modulators, microchannel plate spatial light modulators, photorefractive spatial light modulators, etc. Among them, silicon-based liquid crystal spatial light modulators are the most widely used. They use the optical anisotropy of liquid crystal under the action of an electric field to regulate the incident light field. Through integration with CMOS silicon-based array circuits, they can realize functions such as beam driving, optical holography and beam shaping. The structure and working mechanism of silicon-based liquid crystal spatial light modulators are as follows: Figure 1a-1d As shown. Liquid crystal molecules are rod-shaped molecules. There is a large difference in refractive index along the long axis and short axis of the liquid crystal molecules, showing a very obvious birefringence effect. Liquid crystal material can be considered as a liquid crystal material. It has a certain periodic structure. Under the action of external fields (such as electric fields, light fields, and temperature fields, etc.), the orientation of liquid crystal molecules can rotate, twist, etc. Figure 1a and 1b The shown silicon-based liquid crystal spatial light modulator includes incident light 1, outgoing light 2, anti-reflection film 3, glass upper cover plate 4, ITO transparent electrode 5, upper orientation layer 6, frame sealant 7, spacer 8, liquid crystal layer 9, lower orientation layer 10, metal electrode 11, CMOS circuit board 12 and pixel electrode 13; the liquid crystal layer 9 is arranged between the ITO transparent electrode 5 and the metal electrode 11, and the initial orientation of the liquid crystal molecules is controlled by the upper orientation layer 6 and the lower orientation layer 10. When no bias voltage is applied, the electric field strength between the liquid crystal layers is zero, and the liquid crystal molecules are arranged in the initial orientation, for example Figure 1c The liquid crystal molecules are arranged horizontally in the horizontal orientation shown in 14. When we apply a bias voltage to the spatial modulator, the orientation of the liquid crystal molecules changes under the action of the electric field, as shown in Figure 1dThe liquid crystal molecules are arranged vertically as shown in 15. Due to the birefringence effect of the liquid crystal molecules, its refractive index changes greatly when it is horizontally oriented and vertically oriented (~0.4), so the phase of the incident light after passing through the liquid crystal layer can be changed by external field regulation. The independent modulation of each liquid crystal pixel is achieved through the CMOS circuit board 12 and the corresponding pixel electrode 13, and finally the digital regulation of the entire light field is obtained. Although the silicon-based liquid crystal spatial light modulator can realize the digital regulation of any light field by utilizing the large birefringence effect of the liquid crystal molecules and the CMOS array circuit, the electro-optical regulation response time of the liquid crystal molecules is relatively long (several milliseconds). Due to the limitations of the edge field and the driving voltage, the pixel size of the silicon-based liquid crystal spatial light modulator is still too large compared to the wavelength of the incident light (the pixel size of the existing commercial device is greater than 3μm). These problems lead to the slow response speed of the silicon-based liquid crystal spatial light modulator and the high-order diffraction is too strong when realizing optical holography.

[0003] In order to obtain high-speed optical modulation, people have proposed solid-state spatial light modulators. Currently, the lithium niobate electro-optic modulator is the most commonly used in optical communication networks. Lithium niobate is a nonlinear optical material with an o-light refractive index of about 2.27 and an e-light refractive index of about 2.17. Although the o-light and e-light refractive index changes of lithium niobate are much smaller than those of liquid crystal molecules, since lithium niobate is a solid crystal, its electro-optic modulation response speed is very fast (<1 microsecond). Since the electro-optic modulation voltage of lithium niobate crystals is relatively high and the preparation process of the crystals is incompatible with CMOS silicon-based circuits, lithium niobate crystals are mostly used in the preparation of one-dimensional electro-optic modulators.

[0004] In summary, due to the limitations of electro-optic modulation materials and device structures, existing technologies cannot achieve high-speed two-dimensional array light field phase modulation, so there is a need to develop high-speed, all-solid-state two-dimensional spatial light modulators. Utility Model Content

[0005] The purpose of the utility model is to propose a full-solid-state spatial light modulator based on perovskite crystals to address the problems of slow response speed of existing silicon-based liquid crystal spatial light modulators and difficulty in integrating lithium niobate electro-optical modulators with CMOS array circuits to realize two-dimensional spatial light array modulation. The spatial light modulator utilizes the characteristics of perovskite ion crystals, designs semiconductor junctions such as Schottky junctions or pin junctions, and uses an external electric field to regulate the carrier concentration of the perovskite crystal, thereby changing the effective conductivity of the crystal, and finally changing the phase of the incident light by adjusting the dispersion characteristics of the perovskite crystal. The full-solid-state spatial light modulator based on perovskite crystals proposed in the utility model has sensitive spatial light phase modulation capabilities and fast modulation response speed, which is suitable for the requirements of high-speed optical communications. In addition, the preparation process of the spatial light modulator is compatible with the CMOS circuit backplane, and combined with the CMOS array circuit, it can realize arrayed spatial light field digital control.

[0006] The technical solution adopted by the utility model is: a fully solid-state spatial light modulator based on perovskite crystal, including a perovskite phase modulation layer and a silicon-based CMOS array driving circuit providing digitalization thereto, the silicon-based CMOS array driving circuit including a single crystal silicon substrate, a source electrode, a drain electrode, a gate electrode, a capacitor bottom electrode, a capacitor top electrode, a connecting metal layer, a light-shielding metal layer and a reflective electrode, the perovskite phase modulation layer including a reflective electrode, a perovskite single crystal layer and a transparent electrode;

[0007] The source electrode, the drain electrode and the capacitor bottom electrode are arranged in the single crystal silicon substrate, and a dielectric layer is arranged on the single crystal silicon substrate;

[0008] A gate electrode and a capacitor top electrode are arranged in the dielectric layer, and the gate electrode and the capacitor top electrode are electrically isolated from the single crystal silicon substrate and other electrodes below by the dielectric thin layer;

[0009] A connection metal layer is also provided in the dielectric layer to lead various electrodes upward;

[0010] A light shielding metal layer is also provided in the dielectric layer to block the light irradiated from top to bottom from affecting the CMOS circuit;

[0011] A reflective electrode is arranged on the dielectric layer to provide a bias voltage for the perovskite phase modulation layer and reflect incident light irradiated downward from above;

[0012] The reflective electrode is provided with a perovskite single crystal layer which utilizes a plasma dispersion effect to modulate the phases of incident light and reflected light;

[0013] A transparent electrode is arranged on the perovskite single crystal layer, and the transparent electrode and the reflective electrode work together to form a required electric field distribution in the perovskite single crystal layer.

[0014] The utility model prepares a CMOS array driving circuit on a single crystal silicon substrate, which provides a digital driving voltage to the perovskite phase modulation layer; the perovskite phase modulation layer generates a corresponding bias electric field at different spatial pixel points according to the voltage provided by the CMOS array driving circuit. The plasma dispersion effect of perovskite is utilized to form different phase delays at these spatial pixel points, thereby changing the wavefront of the incident light. In order to obtain stronger plasma dispersion, the phase modulation layer needs to use an ion crystal to increase the concentration change of charged particles under the action of the bias electric field. A typical material is a perovskite crystal.

[0015] Furthermore, the dielectric layer may generally be made of silicon oxide or silicon nitride.

[0016] Furthermore, the work functions of the reflective electrode and the transparent electrode are designed by material selection, so that the reflective electrode, the perovskite single crystal layer and the transparent electrode form a Schottky semiconductor junction, and the Schottky junction is used to enhance the plasma dispersion of the perovskite layer. A typical band structure is that the reflective electrode has a higher work function, and the conduction band of the reflective electrode is lower than the Fermi level of the perovskite single crystal layer; the transparent electrode has a smaller work function, and the conduction band of the transparent electrode is higher than the Fermi level of the perovskite single crystal layer.

[0017] Furthermore, in addition to using a perovskite Schottky junction to obtain phase modulation of the transmitted light by the bias voltage, the utility model also proposes a structure for obtaining phase modulation by using a perovskite pin semiconductor junction, wherein a perovskite n-type layer is arranged on the reflective electrode, a perovskite single crystal layer is arranged on the perovskite n-type layer, a perovskite p-type layer is arranged on the perovskite single crystal layer, and a transparent electrode is arranged on the perovskite p-type layer, which together constitute a perovskite pin junction. Since a perovskite pin junction is used, an ohmic contact can be made between the reflective electrode and the perovskite n-type layer, and an ohmic contact can also be made between the transparent electrode and the perovskite p-type layer.

[0018] The above-mentioned method for preparing a perovskite crystal-based all-solid-state spatial light modulator comprises the following steps:

[0019] 1). A silicon-based CMOS array driving circuit is prepared on a single-crystal silicon substrate using conventional silicon-based microelectronics technology. Its circuit structure is basically the same as the CMOS backplane circuit structure of a silicon-based liquid crystal spatial light modulator. However, the work function of the reflective electrode needs to be selected according to the energy band structure of the perovskite so that it forms a Schottky junction with the perovskite single crystal layer.

[0020] 2). Using the space confinement method to grow a perovskite single crystal layer in a solution on a silicon-based CMOS array drive circuit, the thickness of the perovskite single crystal layer is controlled between 10 μm and 30 μm;

[0021] 3). A transparent electrode is prepared on the perovskite single crystal layer by vacuum evaporation, sputtering or spin coating, and the work function of the electrode is selected so that it forms a Schottky junction with the perovskite single crystal layer;

[0022] 4). Alternatively, the phase modulation of the transmitted light is obtained by using the perovskite pin junction: a first doped metal layer including Bi, Mn, Cu, Sb, and Mg is deposited on the silicon-based CMOS array driving circuit; the thickness of the metal layer is controlled to maintain the insulation between the array pixels;

[0023] 5). Growing a perovskite single crystal layer on the first doped metal layer by the method of step 2), and controlling its thickness within 2 μm; introducing metal ions into the perovskite single crystal layer by heating metal ion diffusion method, and changing its semiconductor properties to n-type;

[0024] 6). Grow a perovskite single crystal layer on the perovskite n-type layer using the method of step 2), and control its thickness to be between 10 μm and 30 μm;

[0025] 7). Depositing a second doped metal layer on the perovskite single crystal layer by the method of step 4), including Ag, Cs, Li, In, and Ba; introducing metal ions into the perovskite single crystal layer by heating metal ion diffusion to change its semiconductor properties to p-type;

[0026] 8). Depositing a transparent electrode on the perovskite p-type layer using the method of step 3);

[0027] The utility model changes the property of the doped metal layer, and a similar method can be used to prepare perovskite pip and nin junctions.

[0028] Beneficial effects of the utility model:

[0029] (1) Although silicon-based liquid crystal spatial light modulation has high pixel resolution and large phase modulation capability, the electro-optical response speed of liquid crystal molecules is slow and cannot fully meet the requirements of high-resolution display, high-speed beam driving and optical communication. The utility model proposes a fully solid-state spatial light modulator based on perovskite crystal, which not only has the advantage of high pixel resolution of silicon-based liquid crystal spatial light modulator, but also has an electro-optical response speed that can be improved to sub-microsecond level. At the same time, its phase delay of the transmitted light can exceed the π phase, so this fully solid-state spatial light modulator can better meet the needs of practical applications.

[0030] (2) Compared with existing solid-state phase modulators such as lithium niobate, the phase modulation of the all-solid-state spatial light modulator based on perovskite crystal proposed by the utility model is more sensitive, and the bias voltage required to obtain π phase modulation is lower. The all-solid-state spatial light modulator based on perovskite crystal proposed by the utility model can also be combined with CMOS array circuits to obtain programmable spatial light wavefront modulation, which is not available in solid-state phase modulators such as lithium niobate. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1a A side view of spatial light modulation of a liquid crystal on silicon spatial light modulator;

[0032] Figure 1b A top view of spatial light modulation of a liquid crystal on silicon spatial light modulator;

[0033] Figure 1c Aligning liquid crystal molecules without bias voltage for liquid crystal on silicon spatial light modulators;

[0034] Figure 1d Applying bias voltage to align liquid crystal molecules of a liquid crystal on silicon spatial light modulator;

[0035] Figure 2 It is an all-solid-state spatial light modulator structure based on perovskite Schottky junction;

[0036] Figure 3a The current-voltage curve of the perovskite phase modulation layer (ohmic contact of the electrodes at both ends);

[0037] Figure 3b The current-voltage curve of the perovskite phase modulation layer (Schottky contact of electrodes at both ends);

[0038] Figure 4 It is a spatial light modulator based on perovskite pin junction;

[0039] Figure 5a Phase modulation of transmitted light for different semiconductor pairs (conventional semiconductor Schottky junction);

[0040] Figure 5b Phase modulation of transmitted light by different semiconductor pairs (perovskite Schottky junction);

[0041] In the figure: 1. Incident light; 2. Outgoing light; 3. Anti-reflection film; 4. Glass upper cover; 5. ITO transparent electrode; 6. Upper orientation layer; 7. Frame sealant; 8. Insulator; 9. Liquid crystal layer; 10. Lower orientation layer; 11. Metal electrode; 12. CMOS circuit board; 13. Pixel electrode; 14. Horizontal arrangement of liquid crystal molecules; 15. Vertical arrangement of liquid crystal molecules; 16. Single crystal silicon substrate; 17. Source electrode; 18. Drain electrode; 19. Gate electrode; 20. Capacitor bottom electrode; 21. Capacitor top electrode; 22. Connecting metal layer; 23. Shading metal layer; 24. Reflective electrode; 25. Perovskite single crystal layer; 26. Transparent electrode; 27. Dielectric layer; 28. Reflective electrode; 29. ​​Perovskite n-type layer; 30. Perovskite p-type layer; 31. Transparent electrode. DETAILED DESCRIPTION

[0042] The utility model is described in detail below. This embodiment is implemented on the premise of the technical solution of the utility model, and a detailed implementation method and a specific operation process are given, but the protection scope of the utility model is not limited to the following embodiments.

[0043] like Figure 2 As shown, a fully solid-state spatial light modulator based on perovskite crystal includes a perovskite phase modulation layer and a silicon-based CMOS array driving circuit providing digitalization thereto, wherein the silicon-based CMOS array driving circuit includes a single crystal silicon substrate 16, a source electrode 17, a drain electrode 18, a gate electrode 19, a capacitor bottom electrode 20, a capacitor top electrode 21, a connecting metal layer 22, a light-shielding metal layer 23 and a reflective electrode 24, and the perovskite phase modulation layer includes a reflective electrode 24, a perovskite single crystal layer 25 and a transparent electrode 26;

[0044] A source electrode 17, a drain electrode 18 and a capacitor bottom electrode 20 are arranged in the single crystal silicon substrate 16, and a dielectric layer 27 is arranged on the single crystal silicon substrate 16, and the dielectric layer 27 can be made of silicon oxide or silicon nitride; a gate electrode 19 and a capacitor top electrode 21 are arranged in the dielectric layer 27, and the gate electrode 19 and the capacitor top electrode 21 are electrically isolated from the single crystal silicon substrate 16 and other electrodes below by a thin dielectric layer; a connecting metal layer 22 for leading various electrodes upward is also arranged in the dielectric layer 27; a light shielding metal layer 23 for blocking the light irradiated from top to bottom from affecting the CMOS circuit is also arranged in the dielectric layer 27; a reflective electrode 24 for providing a bias voltage to the perovskite phase modulation layer and reflecting the incident light irradiated from top to bottom is arranged on the dielectric layer 27; a perovskite single crystal layer 25 for modulating the phase of the incident light and the reflected light by using the plasma dispersion effect is arranged on the reflective electrode 24;

[0045] A transparent electrode 26 is disposed on the perovskite single crystal layer 25 . The transparent electrode 26 and the reflective electrode 24 work together to form a required electric field distribution in the perovskite single crystal layer 25 .

[0046] The utility model is a full solid-state spatial light modulator based on perovskite Schottky junction, wherein a single crystal silicon substrate 16, a source electrode 17, a drain electrode 18, a gate electrode 19, a capacitor bottom electrode 20, a capacitor top electrode 21, a connecting metal layer 22, a light shielding metal layer 23, a reflective electrode 24, and a dielectric layer 27 constitute a CMOS array circuit. The single crystal silicon substrate 16, the source electrode 17, the drain electrode 18, the gate electrode 19, and the dielectric layer 27 constitute a field effect transistor, which turns on or off each spatial light modulator pixel according to the scanning electrical signal of each row; the capacitor bottom electrode 20, the capacitor top electrode 21, and the dielectric layer 27 constitute a charging capacitor, which works together with the aforementioned pixel field effect transistor to enable the spatial light modulator to obtain a holding type working mode. The reflective electrode 24, the perovskite single crystal layer 25, and the transparent electrode 26 constitute a perovskite phase modulation layer. There is a potential barrier between the reflective electrode 24 and the perovskite single crystal layer 25, and there is also a potential barrier between the transparent electrode 26 and the perovskite single crystal layer 25. Due to the effect of these potential barriers, the current passing through the perovskite single crystal layer 25 is nonlinearly related to the bias voltage. Therefore, the plasma dispersion of the perovskite layer can be regulated by the bias voltage, thereby changing the phase of the transmitted light.

[0047] exist Figure 2In the structure of the perovskite spatial light modulator shown, the work functions of the reflective electrode 24 and the transparent electrode 26 need to be designed so that the reflective electrode 24, the perovskite single crystal layer 25 and the transparent electrode 26 form a Schottky semiconductor junction, thereby forming a plasma dispersion of the perovskite layer. A typical structure is that the reflective electrode 24 has a higher work function, and the conduction band of the reflective electrode 24 is lower than the Fermi level of the perovskite single crystal layer 25; the transparent electrode 26 has a smaller work function, and the conduction band of the transparent electrode 26 is higher than the Fermi level of the perovskite single crystal layer 25.

[0048] Figure 3a and 3b This is a typical current-voltage characteristic curve when the electrodes at both ends of the perovskite phase modulation layer are ohmic contacts and Schottky contacts, respectively. It can be seen from the curve that if the electrodes at both ends of the perovskite layer are ohmic contacts, the current and voltage are linearly related, so the conductivity is a constant, and it does not change with the bias voltage. Therefore, changing the bias voltage in this working mode will not cause changes in the plasma dispersion properties of the perovskite layer, and the phase of light transmission cannot be regulated. If the electrodes at both ends of the perovskite layer are Schottky contacts, the current-voltage curve shows obvious nonlinearity, and the conductivity changes significantly with the bias voltage. Therefore, the utility model uses the perovskite Schottky junction to achieve phase modulation of the transmitted light by the bias voltage.

[0049] In addition to using the perovskite Schottky junction to obtain the phase modulation of the transmitted light by the bias voltage, the utility model also proposes a structure that uses the perovskite pin semiconductor junction to obtain the phase modulation, such as Figure 4 shown.

[0050] exist Figure 4 In the structure shown, a perovskite n-type layer 29 is disposed on the reflective electrode 28, a perovskite single crystal layer 25 is disposed on the perovskite n-type layer 29, a perovskite p-type layer 30 is disposed on the perovskite single crystal layer 25, and a transparent electrode 31 is disposed on the perovskite p-type layer 30, which together form a perovskite pin junction. Due to the use of the perovskite pin junction, an ohmic contact can be formed between the reflective electrode 28 and the perovskite n-type layer 29, and an ohmic contact can also be formed between the transparent electrode 31 and the perovskite p-type layer 30. The functional layer composed of the reflective electrode 28, the perovskite n-type layer 29, the perovskite single crystal layer 25, the perovskite p-type layer 30, and the transparent electrode 31 can be obtained. Figure 3b The current-voltage curve is Figure 4 The structure shown can phase modulate the transmitted light. Figure 4 PIP or NIN semiconductor junctions may also be used in the structure shown.

[0051] exist Figure 2 and Figure 4In the spatial light modulator structure shown in the figure, a perovskite single crystal layer is used to control the phase of the transmitted light. If conventional semiconductor materials such as silicon and germanium are used, even if heavy doping technology is used, the carrier concentration is generally limited to 10 19 / cm 3 about. Figure 5a This is a typical change in the loss tangent and phase delay of this type of semiconductor under different bias voltages. It can be seen from the curve that under lower bias voltages, the loss tangent of this type of semiconductor material is very small, so the phase delay it produces through plasma dispersion is also very small. If you want to obtain a larger phase delay, you need to apply a very high bias voltage to the modulator, but this will bring many difficulties to practical applications. Perovskite is an ionic crystal. The binding energy of halogens in its molecular structure is relatively small, and halogen ions are prone to directional ion migration under the action of an electric field. Although this ion migration rate is much smaller than the drift rate of electrons and holes, the ion migration of perovskite has many negative effects on perovskite photovoltaic devices and light-emitting devices. And in Figure 2 and Figure 4 In the perovskite spatial modulator shown, this migration of halide ions produces additional plasmon dispersion. Figure 5b This is a typical loss tangent and phase delay modulation curve of a perovskite Schottky junction. It can be seen that by utilizing the characteristics of perovskite ion crystals, the loss tangent of the perovskite Schottky junction is greatly increased, so it obtains a π phase delay at a bias voltage of 3.5V.

[0052] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the claims attached to the utility model.

Claims

1. A fully solid-state spatial light modulator based on a perovskite crystal, characterized in that: It includes a perovskite phase modulation layer and a silicon-based CMOS array driving circuit providing digitalization thereto, wherein the silicon-based CMOS array driving circuit includes a single crystal silicon substrate, a source electrode, a drain electrode, a gate electrode, a capacitor bottom electrode, a capacitor top electrode, a connecting metal layer, a light-shielding metal layer and a reflective electrode, and the perovskite phase modulation layer includes a reflective electrode, a perovskite single crystal layer and a transparent electrode; The source electrode, the drain electrode and the capacitor bottom electrode are arranged in the single crystal silicon substrate, and a dielectric layer is arranged on the single crystal silicon substrate; A gate electrode and a capacitor top electrode are arranged in the dielectric layer, and the gate electrode and the capacitor top electrode are electrically isolated from the single crystal silicon substrate and other electrodes below by the dielectric thin layer; A connection metal layer is also provided in the dielectric layer to lead various electrodes upward; A light shielding metal layer is also provided in the dielectric layer to block the light irradiated from top to bottom from affecting the CMOS circuit; A reflective electrode is arranged on the dielectric layer to provide a bias voltage for the perovskite phase modulation layer and reflect incident light irradiated downward from above; The reflective electrode is provided with a perovskite single crystal layer which utilizes a plasma dispersion effect to modulate the phases of incident light and reflected light; A transparent electrode is arranged on the perovskite single crystal layer, and the transparent electrode and the reflective electrode work together to form a required electric field distribution in the perovskite single crystal layer.

2. The all-solid-state spatial light modulator based on perovskite crystal according to claim 1, characterized in that: The dielectric layer is made of silicon oxide or silicon nitride.

3. The all-solid-state spatial light modulator based on perovskite crystal according to claim 2, characterized in that: The reflective electrode, the perovskite single crystal layer and the transparent electrode form a Schottky semiconductor junction.

4. The all-solid-state spatial light modulator based on perovskite crystal according to claim 3, characterized in that: A perovskite n-type layer is arranged on the reflective electrode, a perovskite single crystal layer is arranged on the perovskite n-type layer, a perovskite p-type layer is arranged on the perovskite single crystal layer, and a transparent electrode is arranged on the perovskite p-type layer, which together form a perovskite pin junction; there is an ohmic contact between the reflective electrode and the perovskite n-type layer, and there is an ohmic contact between the transparent electrode and the perovskite p-type layer.

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