Techniques for perovskite layer crystallization

1. A method of forming a perovskite material, comprising the steps of:

depositing a metal halide layer on a sample substrate;

vacuum annealing the metal halide layer and methylammonium halide under conditions sufficient to form a vapor of the methylammonium halide which reacts with the metal halide layer and forms a sample comprising the perovskite material on the sample substrate,

wherein, as reaction of the methylammonium halide and the metal halide layer progresses, a color of the sample changes indicating a transition from metal halide to the perovskite material, wherein changes in the color affect optical properties of the sample, the method further comprising the steps of:

monitoring, in real-time, the optical properties of the sample during the vacuum annealing step;

comparing the optical properties of the sample to an end-point standard for the perovskite material; and

stopping the reaction when the optical properties of the sample match the end-point standard.

2. The method of claim 1 , wherein the metal halide layer comprises PbI 2 .

3. The method of claim 1 , wherein the metal halide layer comprises SnI 2 .

4. The method of claim 1 , wherein the methylammonium halide is selected from the group consisting of: methylammonium iodide, methylammonium bromide, and methylammonium chloride.

5. The method of claim 1 , wherein the metal halide layer is formed from a metal halide having a formula MX 2 , wherein M is at least one of Pb and Sn, and X is at least one of F, Cl, Br, and I.

6. The method of claim 5 , wherein M is Pb and Sn, wherein the metal halide comprises Pb m Sn m-l X n Y 2-n , wherein X and Y are each at least one of F, Cl, Br, and I, and wherein 0 <m <1 and 0 ≤n ≤2.

7. The method of claim 1 , wherein the conditions comprise a temperature of from about 60° C. to about 150° C., and ranges therebetween.

8. The method of claim 1 , wherein the conditions comprise a duration of from about 1 minute to about 24 hours, and ranges therebetween.

9. The method of claim 1 , wherein the conditions comprise a pressure of from about 1 ×10 −6 millitor to about 50 Torr, and ranges therebetween.

10. The method of claim 1 , wherein the methylammonium halide is coated on a source substrate, and wherein the source substrate is placed facing the metal halide layer during the vacuum annealing step at a distance d of about 0.2 millimeters to about 20 millimeters, and ranges therebetween away from the metal halide layer.

11. The method of claim 10 , wherein the vacuum annealing step is carried out in a vessel comprising an enclosure sealed to a hot plate, wherein the sample substrate comprising the metal halide layer is placed directly on the hot plate with the metal halide layer facing up, and wherein the source substrate coated with the methylammonium halide is placed the distance d away from the metal halide layer during the vacuum annealing step.

12. The method of claim 11 , wherein the vessel further comprises a spectrometer, and wherein a monitoring module comprising a processor and a memory is connected to the spectrometer and the hot plate, the method further comprising the steps of:

using the spectrometer to monitor, in real-time, the optical properties of the sample during the vacuum annealing step; and

using the monitoring module to automatically stop the reaction when the optical properties of the sample match the end-point standard for the perovskite material by turning off the hot plate.

13. The method of claim 11 , wherein the vessel further comprises an evacuation tube, the method further comprising the steps of:

connecting the evacuation tube to a vacuum pump; and

drawing a vacuum in the vessel using the vacuum pump.

14. A method of forming a perovskite-based photovoltaic device, comprising the steps of:

depositing a first hole transporting or electron transporting material onto an electrically conductive substrate;

depositing a metal halide layer onto the first hole transporting or electron transporting material;

vacuum annealing the metal halide layer and methylammonium halide under conditions sufficient to form a vapor of the methylammonium halide which reacts with the metal halide layer and forms a sample comprising a perovskite material on the electrically conductive substrate, wherein, as reaction of the methylammonium halide and the metal halide layer progresses, a color of the sample changes indicating a transition from metal halide to the perovskite material, and wherein changes in the color affect optical properties of the sample;

monitoring, in real-time, the optical properties of the sample during the vacuum annealing step;

comparing the optical properties of the sample to an end-point standard for the perovskite material;

stopping the reaction when the optical properties of the sample match the end-point standard;

depositing a second hole transporting or electron transporting material onto the perovskite material which has an opposite polarity from the first hole transporting or electron transporting material; and

depositing an electrically conductive material onto the second hole transporting or electron transporting material.

15. The method of claim 14 , wherein the metal halide layer is formed from a metal halide having a formula MX 2 , wherein M is at least one of Pb and Sn, and X is at least one of F, Cl, Br, and I.

16. The method of claim 15 , wherein M is Pb and Sn, wherein the metal halide comprises Pb m Sn m-l X n Y 2-n , wherein X and Y are each at least one of F, Cl, Br, and I, and wherein 0 <m <1 and 0 ≤n ≤2.

17. The method of claim 14 , wherein the conditions comprise at least one of a temperature of from about 60° C. to about 150° C., and ranges therebetween, a duration of from about 1 minute to about 24 hours, and ranges therebetween, and a pressure of from about 1 ×10 −6 millitor to about 50 Torr, and ranges therebetween.

18. The method of claim 14 , wherein the methylammonium halide is selected from the group consisting of: methylammonium iodide, methylammonium bromide, and methylammonium chloride.

19. The method of claim 14 , wherein the vacuum annealing step is carried out in a vessel comprising an enclosure sealed to a hot plate with the sample substrate comprising the metal halide layer being placed directly on the hot plate with the metal halide layer facing up, wherein the source substrate coated with the methylammonium halide is placed the distance d away from the metal halide layer during the vacuum annealing step, wherein the vessel further comprises a spectrometer, and wherein a monitoring module comprising a processor and memory is connected to the spectrometer and the hot plate, the method further comprising the steps of:

using the spectrometer to monitor, in real-time, the optical properties of the sample during the vacuum annealing step; and

using the monitoring module to automatically stop the reaction when the optical properties of the sample match the end-point standard for the perovskite material by turning off the hot plate.