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A light emitting device including semiconductor nanocrystals can have a unipolar construction. The semiconductor nanocrystals emit light during device operation. The size and chemical composition of the semiconductor nanocrystals can be chosen to provide desired emission characteristics. Devices tha

A light emitting device including semiconductor nanocrystals can have a unipolar construction. The semiconductor nanocrystals emit light during device operation. The size and chemical composition of the semiconductor nanocrystals can be chosen to provide desired emission characteristics. Devices that share a substrate and emit more than one color may be conveniently made.

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1. A light emitting device comprising: a first electrode;a first semiconductor material adjacent to the first electrode;a second electrode;a second semiconductor material adjacent to the second electrode; andan emissive layer between the first semiconductor material and the second semiconductor mate

1. A light emitting device comprising: a first electrode;a first semiconductor material adjacent to the first electrode;a second electrode;a second semiconductor material adjacent to the second electrode; andan emissive layer between the first semiconductor material and the second semiconductor material, wherein the emissive layer includes a plurality of semiconductor nanocrystals, wherein the semiconductor nanocrystals are colloidally grown, and wherein the first semiconductor material and the second semiconductor material have the same polarity. 2. The light emitting device of claim 1, wherein the first semiconductor material and the second semiconductor material are each n-type semiconductor materials. 3. The light emitting device of claim 2, further comprising a first electron-blocking layer between the first n-type semiconductor material and the emissive layer. 4. The light emitting device of claim 2, wherein the first n-type semiconductor material includes a ZTO or the second n-type semiconductor material includes a ZTO. 5. The light emitting device of claim 4, further comprising a first electron-blocking layer between the first n-type semiconductor material and the emissive layer, and a first insulating layer between the first electron-blocking layer and the emissive layer. 6. The light emitting device of claim 5, further comprising a second electron-blocking layer between the second n-type semiconductor material and the emissive layer, and a second insulating layer between the second electron-blocking layer and the emissive layer. 7. The light emitting device of claim 5, further comprising a second electron-blocking layer between the second n-type semiconductor material and the emissive layer, and a second insulating layer between the second electron-blocking layer and the emissive layer. 8. The light emitting device of claim 7, wherein at least one of the first and second electron-blocking layers includes ZnS. 9. The light emitting device of claim 7, wherein at least one of the first and insulating layers includes ZnO. 10. The light emitting device of claim 3, further comprising a first insulating layer between the first electron-blocking layer and the emissive layer. 11. The light emitting device of claim 3, further comprising a second electron-blocking layer between the second n-type semiconductor material and the emissive layer. 12. The light emitting device of claim 10, further comprising a second insulating layer between the second electron-blocking layer and the emissive layer. 13. The light emitting device of claim 1, wherein the device is substantially transparent to at least a portion of visible wavelengths of light. 14. The light emitting device of claim 1, wherein the plurality of semiconductor nanocrystals includes a first population of semiconductor nanocrystals selected to emit a single color of light. 15. The light emitting device of claim 14, wherein the plurality of semiconductor nanocrystals includes more than one distinct populations of nanocrystals selected to emit more than one different color of light. 16. The light emitting device of claim 15, wherein the plurality of semiconductor nanocrystals are selected to produce a white light emission from the device. 17. The light emitting device of claim 14, wherein the first population of semiconductor nanocrystals is selected to emit visible light. 18. The light emitting device of claim 14, wherein the first population of semiconductor nanocrystals is selected to emit infrared light. 19. The light emitting device of claim 1, wherein the device is unpackaged. 20. The light emitting device of claim 1, wherein the first semiconductor material and the second semiconductor material are each p-type semiconductor materials. 21. The light emitting device of claim 1, wherein each of first semiconductor material and the second semiconductor material is an inorganic semiconductor material. 22. A method of forming a device, comprising: depositing a first n-type semiconductor material adjacent to the first electrode;depositing over the first n-type semiconductor material an emissive layer including a plurality of semiconductor nanocrystals, wherein the semiconductor nanocrystals are colloidally grown;depositing over the emissive layer a second n-type semiconductor material; andassembling a second electrode adjacent to the second n-type semiconductor material. 23. A method of generating light comprising: providing a device including a first electrode; a first n-type semiconductor material adjacent to the first electrode; a second electrode; a second n-type semiconductor material adjacent to the second electrode; and an emissive layer between the first n-type semiconductor material and second n-type semiconductor material, wherein the emissive layer includes a plurality of semiconductor nanocrystals, and wherein the semiconductor nanocrystals are colloidally grown; andapplying a light-generating potential across the first electrode and the second electrode. 24. The method of claim 23, wherein light is generated continuously for at least 20 hours with a substantially constant luminosity, and wherein the device is unpackaged. 25. A light emitting device, comprising: a first electrode;a first n-type semiconductor material including ZTO adjacent to the first electrode;a second electrode;a second n-type semiconductor material including ZTO adjacent to the second electrode; andan emissive layer between the first n-type semiconductor material and second n-type semiconductor material, wherein the emissive layer includes a plurality of semiconductor nanocrystals, and wherein the semiconductor nanocrystals are colloidally grown.