Methods for making low bandgap perovskites
The present disclosure relates to a composition that includes a perovskite having a stoichiometry comprising A 1-x FA x Sn 1-y B y (I 1-z X z ) 3 , where A is a first cation, B is a second cation, X is a halide, and 0.5≤x≤0.9, 0.5≤y≤0.9, and 0≤z≤1. In some embodiments of the present disclosure, A may include at least one of cesium, guanidinium, and/or methylammonium. In some embodiments of the present disclosure, X may include at least one of bromide and/or chloride. In some embodiments of the present disclosure, z may be equal to zero.
1. A composition comprising:
a perovskite layer having a stoichiometry comprising Cs 1-x FA x Sn 1-y Pb y (I 1-z X z ) 3 , wherein:
the perovskite layer has an average grain size of 865 nm±360 nm,
X is a halide,
0.5≤x≤0.9, 0.5≤y≤0.9, and 0≤z≤1.
2. The composition of claim 1 , wherein X comprises at least one of bromide or chloride.
3. The composition of claim 1 , wherein z equals zero.
4. The composition of claim 1 , further comprising a bandgap between about 1.1 eV and about 1.5 eV.
5. The composition of claim 4 , wherein the bandgap is between about 1.3 eV and about 1.4 eV.
6. The composition of claim 1 , further comprising a biaxial residual stress level between about 0 MPa and about 100 MPa.
7. The composition of claim 6 , wherein the biaxial residual stress level is between about 0 MPa and about 40 MPa.
8. The composition of claim 1 , further comprising a dark carrier density between about 1×10 13 cm −3 and about 1×10 17 cm −3 .
9. The composition of claim 8 , wherein the dark carrier density is between about 5×10 14 cm −3 and about 5×10 16 cm −3 .
10. The composition of claim 1 , wherein the stoichiometry comprises Cs 1-x FA x Sn 1-y Pb y I 3 .
11. The composition of claim 10 , wherein 0.6≤x≤0.8 and 0.6≤y≤0.8.
12. A method of making a perovskite, the method comprising:
combining a stoichiometric amount of at least one perovskite precursor comprising cesium, formamidinium (FA), tin, and at least one of iodide or X resulting in a mixture;
adding an additive to the mixture; and
treating the mixture, wherein:
the treating results in forming a perovskite layer having a stoichiometry comprising Cs 1-x FA x Sn 1-y Pb y (I 1-z X z ) 3 ,
the perovskite layer has an average grain size of 865 nm±360 nm,
X is a halide other than iodide,
0.5≤x≤0.9, 0.5≤y≤1, 0.9, 0≤z≤1, and
the additive comprises FA and tin and at least one of fluoride or chloride.
13. The method of claim 12 , wherein the additive is added at a concentration between about 0.1 mol % and about 10 mol % relative to the stoichiometric amount.
14. The method of claim 13 , wherein the concentration is between about 0.1 mol % and about 5 mol %.
15. The method of claim 12 , wherein:
the additive comprises at least one of SnF 2 ·nFACl or SnCl 2 ·nFACl.
16. The method of claim 15 , wherein 2.5≤n≤3.5.
17. The composition of claim 1 , wherein the perovskite layer has a grain boundary width less than 45 nm.
18. The composition of claim 17 , wherein the perovskite layer has less than 3 grains/μm 2 .
19. The method of claim 12 , wherein the perovskite layer has a grain boundary width less than 45 nm.
20. The method of claim 19 , wherein the perovskite layer has less than 3 grains/μm 2 .