System and method for fabricating perovskite film for solar cell applications

Abstract

A system and method for fabricating perovskite films for solar cell applications are provided, the system including a housing for use as a vacuum chamber, a substrate stage coupled to the top section of the housing; a first evaporator unit coupled to the bottom section of the housing and configured to generate BX 2 (metal halide material) vapor; a second evaporator unit coupled to the housing and configured to generate AX (organic material) vapor; and a flow control unit coupled to the housing for controlling circulation of the AX vapor. The dimensions of the horizontal cross-sectional shape of the first evaporator unit, the dimensions of the horizontal cross-sectional shape of the substrate stage, and the relative position in the horizontal direction between the two horizontal cross-sectional shapes are configured to maximize the overlap between the two horizontal cross-sectional shapes.

1 : A system for fabricating a perovskite film for solar cell applications, by using source materials AX and BX 2 , wherein the AX is an organic halide material and the BX 2  is a metal halide material, wherein the halogen X in the AX and the halogen X in the BX 2  are the same element or different elements, the system comprising:
 a housing for use as a vacuum chamber, the housing having a side section along a vertical direction and top and bottom sections along a horizontal direction;   a substrate stage coupled to the top section of the housing and configured to have a stage surface facing vertically downward for a substrate to be placed on;   a first evaporator unit coupled to the bottom section of the housing and configured to generate BX 2  vapor;   a second evaporator unit coupled to the housing and configured to generate AX vapor; and   a flow control unit coupled to the housing for controlling circulation of the AX vapor in the housing,   wherein dimensions of a horizontal cross-sectional shape of the first evaporator unit, dimensions of a horizontal cross-sectional shape of the substrate stage, and a relative position in the horizontal direction between the two horizontal cross-sectional shapes are configured to maximize an overlap between the two horizontal cross-sectional shapes.   
     
     
         2 : The system of  claim 1 , wherein
 the stage surface of the substrate stage is configured to have an area for accommodating a substrate having a size of 5 cm×5 cm or larger, wherein the substrate is a one-piece substrate or a collection of a plurality of substrates.   
     
     
         3 : The system of  claim 1 , wherein
 the substrate stage, the first evaporator unit, the second evaporator unit and the flow control unit are configured to enable deposition of the BX 2  vapor to be substantially directional, following line-of-sight transfer from the first evaporator unit to the substrate, while enabling deposition of the AX to be substantially less directional based on the AX vapor circulating in the housing.   
     
     
         4 : The system of  claim 1 , wherein
 the flow control unit is configured to control the circulation of the AX vapor to generate a substantially uniform flow of the AX vapor over the substrate.   
     
     
         5 : The system of  claim 1 , wherein
 the flow control unit includes a fan system, a pump system or a combination thereof.   
     
     
         6 : The system of  claim 1 , further comprising:
 a first shutter provided below the substrate stage and configured to be moved to expose or cover the substrate stage to control deposition of the BX 2  vapor onto the substrate; and   a second shutter provided above the first evaporator unit and configured to be moved to expose or cover the first evaporator unit to control a flow of the BX 2  vapor.   
     
     
         7 : The system of  claim 1 , wherein
 temperature of the substrate stage is controlled to provide uniform cooling or heating to the substrate in a range between −190° C. to 200° C.   
     
     
         8 : The system of  claim 7 , wherein
 the temperature of the substrate stage is controlled to have the substrate at a room temperature in a range between 15° C. to 25° C.   
     
     
         9 : The system of  claim 1 , wherein
 a first evaporation temperature associated with the first evaporator unit is controlled to adjust a first evaporation rate for generating the BX 2  vapor.   
     
     
         10 : The system of  claim 9 , wherein
 the first evaporator unit includes a container for containing the BX 2  in powder form and a heating element configured to heat the container uniformly, wherein the heating element is controlled to provide the first evaporation temperature to adjust the first evaporation rate for generating the BX 2  vapor.   
     
     
         11 : The system of  claim 1 , wherein
 a second evaporation temperature associated with the second evaporator unit is controlled to adjust a second evaporation rate for generating the AX vapor.   
     
     
         12 : The system of  claim 11 , wherein
 the second evaporator unit includes a container for containing the AX in powder form and a heating element configured to heat the container uniformly, wherein the heating element is controlled to provide the second evaporation temperature to adjust the second evaporation rate for generating the AX vapor.   
     
     
         13 : The system of  claim 1 , wherein
 the second evaporator unit is coupled to the side section of the housing.   
     
     
         14 : The system of  claim 1 , wherein
 the second evaporator unit is coupled to the bottom section of the housing.   
     
     
         15 : The system of  claim 14 , further comprising:
 a shield between the first evaporator unit and the second evaporator unit to reduce thermal interference therebetween.   
     
     
         16 : The system of  claim 1 , wherein
 the second evaporator unit includes a valve or an evaporator shutter for controlling a flux of the AX vapor exiting from the second evaporator unit.   
     
     
         17 : The system of  claim 1 , further comprising:
 a gate valve coupled between the housing and a pump unit for controlling pressure inside the housing to a value optimal for a chemical reaction between the source materials and for efficient use of the source materials.   
     
     
         18 : The system of  claim 17 , wherein
 the gate valve is configured to assume at least first and second positions, wherein the first position is for use for controlling AX vapor pressure to stabilize the circulation of the AX vapor and the second position is for use for pumping out remaining vapor from the housing after deposition is completed.   
     
     
         19 : The system of  claim 1 , further comprising:
 a first monitor for monitoring the BX 2  vapor and thickness of the perovskite film growing on the substrate.   
     
     
         20 : The system of  claim 1 , further comprising:
 a second monitor for monitoring the AX vapor.   
     
     
         21 : The system of  claim 1 , wherein
 temperature of the housing is kept at about 70° C.   
     
     
         22 : The system of  claim 1 , further comprising:
 a second housing for use as a load-lock chamber;   a second gate valve coupled between a second pump unit and the second housing, the second gate valve and the second pump being configured for controlling pressure inside the second housing;   a third gate valve coupled between the housing and the second housing for controlling communication therebetween; and   a sample transfer system coupled to the housing for transferring the substrate between the housing and the second housing.   
     
     
         23 : The system of  claim 22 , wherein
 the sample transfer system includes:   a mechanical device for holding and releasing an object; and   a rod coupled to the mechanical device for controlling movement of the mechanical device.   
     
     
         24 : The system of  claim 23 , wherein
 the second housing is configured to store the substrate, and the second pump unit and the second gate valve are controlled to have a predetermined pressure level in the second housing while the third gate valve is closed;   after evaporation temperatures for the source materials are controlled and the flow control unit is controlled to circulate the AX vapor in the housing, the third gate valve is opened, and the mechanical device is moved to reach and hold the substrate in the second housing and moved back to the housing to release and place the substrate on the substrate stage; and thereafter the third gate valve is closed.   
     
     
         25 : The system of  claim 24 , wherein
 after a predetermined thickness of the perovskite film is attained, the third gate valve is opened, and the mechanical device is moved to reach and hold the substrate on which the perovskite film is grown in the housing, moved to the second housing to release and place the substrate on which the perovskite film is grown in the second housing, and moved back to the housing; and thereafter the third gate valve is closed.   
     
     
         26 : A method for fabricating a perovskite film for solar cell applications, by using source materials AX and BX 2 , wherein the AX is an organic halide material and the BX 2  is a metal halide material, wherein the halogen X in the AX and the halogen X in the BX 2  are the same element or different elements, and by using a system comprising:
 a housing for use as a vacuum chamber, the housing having a side section along a vertical direction and top and bottom sections along a horizontal direction;   a substrate stage coupled to the top section of the housing and configured to have a stage surface facing vertically downward for a substrate to be placed on;   a first evaporator unit coupled to the bottom section of the housing and configured to generate BX 2  vapor;   a second evaporator unit coupled to the housing and configured to generate AX vapor;   a flow control unit coupled to the housing for controlling circulation of the AX vapor in the housing;   a gate valve coupled between the housing and a pump unit for controlling pressure inside the housing;   a first shutter provided below the substrate stage and configured to be moved to expose or cover the substrate stage;   and a second shutter provided above the first evaporator unit and configured to be moved to expose or cover the first evaporator unit, the method comprising:
 controlling temperature of the substrate stage for providing uniform cooling or heating to the substrate; 
 moving the first shutter to cover the substrate; 
 moving the second shutter to expose the first evaporator unit; 
 opening the gate valve to a first position; 
 controlling a first evaporation temperature associated with the first evaporator unit to adjust a first evaporation rate for generating the BX 2  vapor; 
 controlling a second evaporation temperature associated with the second evaporator unit to adjust a second evaporation rate for generating the AX vapor; 
 controlling the flow control unit to control the circulation of the AX vapor; 
 moving the first shutter to expose the substrate; 
 monitoring thickness of the perovskite film growing on the substrate; 
 moving the first shutter to cover the substrate when the thickness of the perovskite film reaches a predetermined thickness; 
 terminating heating of the first and second evaporator units; and 
 opening the gate valve to a second position to pump out remaining vapor inside the housing, 
 wherein dimensions of a horizontal cross-sectional shape of the first evaporator unit, dimensions of a horizontal cross-sectional shape of the substrate stage, and a relative position in the horizontal direction between the two horizontal cross-sectional shapes are configured to maximize an overlap between the two horizontal cross-sectional shapes. 
   
     
     
         27 : The method of  claim 26 , wherein
 the substrate stage, the first evaporator unit, the second evaporator unit and the flow control unit are configured to enable deposition of the BX 2  vapor to be substantially directional, following line-of-sight transfer from the first evaporator unit to the substrate, while enabling deposition of the AX to be substantially less directional based on the AX vapor circulating in the housing.   
     
     
         28 : The method of  claim 26 , wherein
 the stage surface of the substrate stage is configured to have an area for accommodating a substrate having a size of 5 cm×5 cm or larger, wherein the substrate is a one-piece substrate or a collection of a plurality of substrates.   
     
     
         29 : The method of  claim 26 , wherein
 the controlling the temperature of the substrate stage comprises controlling the temperature of the substrate stage to have the substrate at a room temperature in a range between 15° C. to 25° C.   
     
     
         30 : The method of  claim 26 , further comprising
 placing the substrate on the substrate stage prior to the controlling the temperature of the substrate stage.   
     
     
         31 : The method of  claim 26 , wherein the system further comprises:
 a second housing for use as a load-lock chamber;   a second gate valve coupled between a second pump unit and the second housing, the second gate valve and the second pump being configured for controlling pressure inside the second housing;   a third gate valve coupled between the housing and the second housing for controlling communication therebetween;   and a sample transfer system coupled to the housing for transferring the substrate between the housing and the second housing, the method further comprising:
 storing the substrate in the second housing; 
 controlling the second pump unit and the second gate valve to have a predetermined pressure level in the second housing while the third gate valve is closed; 
 opening the third gate valve; 
 controlling the sample transfer system to reach and hold the substrate in the second housing and transfer the substrate from the second housing to the housing, and to release and place the substrate on the substrate stage; and 
 closing the third gate valve, 
 wherein the opening through the closing the third gate valve are carried out after the controlling the flow control unit to control the circulation of the AX vapor and prior to the moving the first shutter to expose the substrate. 
   
     
     
         32 : The method of  claim 31 , further comprising:
 opening the third gate valve;   
       controlling the sample transfer system to reach and hold the substrate on which the perovskite film is grown in the housing and transfer the substrate on which the perovskite film is grown from the housing to the second housing, and to release and place the substrate on which the perovskite film is grown in the second housing; and
 closing the third gate valve, 
 wherein the opening through the closing the third gate valve are carried out after the opening the gate valve to a second position to pump out remaining vapor inside the housing. 
 
     
     
         33 : A perovskite film that has a perovskite structure having ABX 3  structure as a unit cell, where A is MA, FA or 5-AVA, B is Pb or Sn, and X is Cl, I or Br,
 wherein an X-ray diffraction spectrum of the perovskite film has a (110) plane peak, a (220) plane peak and a (330) plane peak within a surface area of 5 cm×5 cm or larger.   
     
     
         34 : The perovskite film of  claim 33 , wherein the perovskite film is a CH 3 NH 3 PbI 3-X Cl X  film, and the X-ray diffraction spectrum of the perovskite film does not have a peak at 15.7° within the surface area of 5 cm×5 cm or larger.