Organic-inorganic perovskite materials and methods of making the same

1. A method comprising:

treating a liquid comprising a first precursor at a concentration C 1 , a second precursor at a concentration C 2 , a third precursor at a concentration C 3 , a fourth precursor, and an additive at a concentration C 4 , wherein:

the first precursor comprises cesium and a first halide comprising at least one of iodide or bromide,

the second precursor comprises formamidinium (FA) and a second halide comprising at least one of iodide or bromide,

the third precursor comprises PbBr 2 ,

the fourth precursor comprises PbI 2 ,

the additive comprises at least one of methylammonium bromide (MABr) or methylammonium iodide (MAI),

the treating results in a perovskite comprising FA x Cs 1-x Pb(I y Br 1-y ) 3 that is substantially free of MA,

0 <x<1,

0 <y<1,

each of C 1 , C 2 , and C 3 are between 0.001 M and 100 M, inclusively, and

at least one of C 4 /C 1 or C 4 /C 2 equals a ratio greater than or equal to zero.

2. The method of claim 1 , wherein the ratio is between greater than zero and less than 0.5.

3. The method of claim 1 , wherein the composition comprises approximately FA 0.83 Cs 0.17 Pb(I 0.6 Br 0.4 ) 3 .

4. The method of claim 1 , wherein the perovskite has a bandgap greater than or equal to 1.6 eV.

5. The method of claim 1 , wherein the liquid comprises a solvent.

6. The method of claim 5 , wherein the treating comprises heating the liquid resulting in removal of the solvent.

7. The method of claim 5 , wherein the treating comprises exposing the liquid to a gas stream resulting in removal of the solvent.

8. The method of claim 1 , wherein the first halide is different than the second halide.