Eliminating emissive sub-bandgap states in nanocrystals
The size-dependent band-gap tunability and solution processability of nanocrystals (NCs) make them attractive candidates for optoelectronic applications. One factor that presently limits the device performance of NC thin films is sub-bandgap states, also referred to as trap states. Trap states can be controlled by surface treatment of the nanocrystals.
1. A method of modifying a surface of nanocrystal including contacting a surface of the nanocrystal with an oxidizing agent, wherein the nanocrystal is a Group II-VI compound, a Group II-V compound, a Group III-VI compound, a Group III-V compound, a Group IV-VI compound, a Group I-III-VI compound, a Group II-IV-VI compound, or a Group II-IV-V compound,
treating the surface with the oxidizing agent until a density of trap states for the nanocrystal having the oxidized surface compared to the nanocrystal having an untreated surface is reduced by at least 20-fold and
removing under-charged atoms on the surface.
2. The method of claim 1 , wherein the nanocrystal includes Pb.
3. The method of claim 1 , wherein the nanocrystal includes S.
4. The method of claim 1 , wherein the nanocrystal includes Se.
5. The method of claim 1 , wherein the oxidizing agent is selected from the group consisting of 1, 4-benzoquinone, dithiothreitol, 2,3-dichloro-5,6-dicyanobenzoquinone, 3,3′,5,5′-tetra-tert-butyldiphenoquinone, di-tert-butyl peroxide, I 2 , I 2 /I − (I 3 − ), chlorine gas, bromine, ozone, O 2 plasma treatment, and an acid, or combinations thereof.
6. The method of claim 1 , wherein the oxidizing agent is pyruvic acid and the method includes annealing.
7. The method of claim 1 , wherein contacting a surface of the nanocrystal with the oxidizing agent to oxidize metal atom of the nanocrystal atoms at the surface.
8. A method of treating a film that includes nanocrystal comprising contacting a surface of the nanocrystal with an oxidizing agent, wherein the nanocrystal is a Group II-VI compound, a Group II-V compound, a Group III-VI compound, a Group III-V compound, a Group IV-VI compound, a Group I-III-VI compound, a Group II-IV-VI compound, or a Group II-IV-V compound,
forming a modified surface in which a density of trap states for the nanocrystal having the oxidized surface compared to the nanocrystal having an untreated surface is reduced by at least 20-fold and
removing under-charged atoms on the film with the oxidizing agent.
9. The method of claim 8 , wherein the nanocrystal includes Pb.
10. The method of claim 8 , wherein the nanocrystal includes S.
11. The method of claim 8 , wherein the nanocrystal includes Se.
12. The method of claim 8 , wherein the oxidizing agent is selected from the group consisting of 1, 4-benzoquinone, dithiothreitol, 2,3-dichloro-5,6-dicyanobenzoquinone, 3,3′,5,5′-tetra-tert-butyldiphenoquinone, di-tert-butyl peroxide, I 2 , I 2 /I − (I 3 − ), chlorine gas, bromine, ozone, O 2 plasma treatment, and an acid, or combinations thereof.
13. The method of claim 8 , wherein the oxidizing agent is pyruvic acid and the method includes annealing.
14. The method of claim 8 , wherein contacting a surface of the nanocrystal with the oxidizing agent to oxidize metal atom of the nanocrystal atoms at the surface.
15. The method of claim 8 , wherein contacting the surface of the nanocrystal with the oxidizing agent is dispensing the oxidizing agent onto the film.
16. The method of claim 1 , wherein the oxidizing agent is selected from the group consisting of H 2 SO 4 , HNO 3 , 1, 4-benzoquinone, dithiothreitol, 2,3-dichloro-5,6-dicyanobenzoquinone, 3,3′,5,5′-tetra-tert-butyldiphenoquinone, di-tert-butyl peroxide, I 2 , I 2 /I − (I 3 − ), and pyruvic acid.
17. The method of claim 8 , wherein the oxidizing agent is selected from the group consisting of H 2 SO 4 , HNO 3 , 1, 4-benzoquinone, dithiothreitol, 2,3-dichloro-5,6-dicyanobenzoquinone, 3,3′,5,5′-tetra-tert-butyldiphenoquinone, di-tert-butyl peroxide, I 2 , I 2 /I − (I 3 − ), and pyruvic acid.
18. The method of claim 1 , wherein the oxidizing agent is selected from the group consisting of 1, 4-benzoquinone, dithiothreitol, 2,3-dichloro-5,6-dicyanobenzoquinone, 3,3′,5,5′-tetra-tert-butyldiphenoquinone, di-tert-butyl peroxide, I 2 , I 2 /I − (I 3 − ), bromine, ozone, and an acid, or combinations thereof.
19. The method of claim 8 , wherein the oxidizing agent is selected from the group consisting of 1, 4-benzoquinone, dithiothreitol, 2,3-dichloro-5,6-dicyanobenzoquinone, 3,3′,5,5′-tetra-tert-butyldiphenoquinone, di-tert-butyl peroxide, I 2 , I 2 /I − (I 3 − ), bromine, ozone, and an acid, or combinations thereof.