Methods of making bandgap-tunable perovskite materials

1. A method of making a mixed halide perovskite composition comprising:

depositing a first portion of a first precursor solution comprising Cs or Pb on a substrate; and

depositing a first portion of a second precursor solution comprising Pb or Cs on the substrate, either sequential to or simultaneous with the deposition of the first portion of the first precursor solution,

wherein (i) when the first portion of the first precursor solution comprises Cs, at least a portion of the second precursor solution comprises Pb, and (ii) when the first portion of the first precursor solution comprises Pb, at least a portion of the second precursor solution comprises Cs,

wherein the depositing of the first and second precursor solutions is carried out in a manner effective to produce a mixed halide composition in the form of a perovskite embedded in a non-perovskite matrix,

wherein the perovskite is in the form of nanocrystals having the formula: CsPb(A x B y ) 3 and the non-perovskite matrix has the formula: Cs 4 Pb(A x B y ) 6 ,

wherein A and B are each a halogen,

wherein x and y are non-zero and x+y=1,

wherein the mixed halide perovskite composition has a morphology which suppresses phase segregation of the mixed halide perovskite composition when subjected to optical or electrical stimuli to stabilize a tuned bandgap of the mixed halide perovskite composition.

2. The method of claim 1 , wherein the step of depositing a first portion of the first precursor solution on the substrate and the step of depositing a first portion of the second precursor solution on the substrate are performed simultaneously.

3. The method of claim 1 , wherein the step of depositing a first portion of the first precursor solution on the substrate and the step of depositing a first portion of the second precursor solution on the substrate are performed sequentially.

4. The method of claim 1 , wherein the first precursor solution comprises CsBr or CsI and wherein the second precursor solution comprises PbI 2 or PbBr 2 .

5. The method of claim 1 , wherein the substrate comprises glass.

6. The method of claim 1 , further comprising:

depositing a second portion of the first precursor solution on the substrate; and

depositing a second portion the second precursor solution on the substrate, either sequential to or simultaneous with the deposition of the second portion of the first precursor solution, wherein the second portions of the first and second precursor solutions are deposited on the first portions of the first and second precursor solutions.

7. The method of claim 1 , wherein the depositing of the first and second precursor solutions is performed by a physical vapor deposition process.

8. The methods of claim 7 , further comprising thermal annealing the first and second precursors following their deposition on the substrate.

9. The method of claim 1 , wherein A and B are selected from iodine and bromine.

10. The method of claim 1 , wherein x is ⅓ and y is ⅔, or x is ⅔ and y is ⅓.

11. The method of claim 1 , wherein the mixed halide composition comprises a Cs(I x ) 3 layer and a Pb(Br y ) 3 layer.

12. The method of claim 1 , wherein the mixed halide composition comprises a Cs(Br y ) 3 layer and a Pb(I x ) 3 layer.

13. The method of claim 1 , wherein the mixed halide composition comprises a CsPb(I x Br y ) 3 layer.

14. The method of claim 1 , wherein the mixed halide composition has (i) a normalized photoluminescence of from about 500 nm to about 650 nm, or (ii) a UV-vis absorption peak between from about 225 nm to about 600 nm.

15. The method of claim 1 , wherein:

the nanocrystals are in the form of photo-active crystallites of perovskite having the formula CsPb(I y Br x ) 3 , and

the non-perovskite matrix is in the form of photo-inactive insulating crystallites in which the photo-active crystallites are embedded.

16. The method of claim 15 , wherein the mixed halide composition is the form of a film formed by a physical deposition process.