PHOTOVOLTAIC DEVICE WITH GRADED BUFFER LAYER

1 . A method of manufacturing a photovoltaic device, comprising:

forming a semiconductor absorber layer adjacent to a substrate, wherein the semiconductor absorber layer comprises copper, indium, gallium, selenium and/or sulfur; and

forming a buffer layer adjacent to the semiconductor absorber layer, wherein forming the buffer layer comprises forming a first metal chalcogenide layer having a first bandgap adjacent to the semiconductor absorber layer and forming a second metal chalcogenide layer having a second bandgap adjacent to the first metal chalcogenide layer, wherein forming the first metal chalcogenide layer comprises pulsing a first metal precursor and pulsing a first chalcogen precursor and forming the second metal chalcogenide layer comprises pulsing a second metal precursor and pulsing a second chalcogen precursor.

2 . The method of claim 1 , wherein forming the first metal chalcogenide layer comprises forming one or more first metal chalcogenide monolayers and forming the second metal chalcogenide layer comprises forming one or more second metal chalcogenide monolayers.

3 . The method of claim 2 , wherein each of the first metal chalcogenide monolayers comprises a same first metal chalcogenide.

4 . The method of claim 2 , wherein each of the second metal chalcogenide monolayers comprises a same second metal chalcogenide.

5 . The method of claim 1 , further comprising forming a conducting layer adjacent to the substrate before forming the semiconductor absorber layer adjacent to the substrate.

6 . The method of claim 1 , further comprising:

forming a transparent conductive oxide layer adjacent to the buffer layer; and

forming a semiconductor window layer adjacent to the buffer layer.

7 . The method of claim 1 , wherein each of the first and second metal precursors comprises a material selected from the group consisting of indium, zinc, trimethylindium, indium acetylacetonate, indium chloride, dimethylzinc and trimethylzinc.

8 . The method of claim 1 , wherein each of the first and second chalcogen precursors comprises a material selected from the group consisting of oxygen, sulfur, selenium, water, ozone, sulfur dioxide, hydrogen sulfide, hydrogen selenide, and diethylselenide.

9 . The method of claim 1 , wherein each of the first and second metal chalcogenide layers comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

10 . The method of claim 1 , further comprising forming a third metal chalcogenide layer adjacent to the first metal chalcogenide layer before forming the second metal chalcogenide layer, wherein the third metal chalcogenide layer has a bandgap different from the first bandgap and the second bandgap.

11 . The method of claim 10 , wherein forming the third metal chalcogenide layer comprises pulsing a third metal precursor and pulsing a third chalcogen precursor.

12 . The method of claim 10 , wherein the third metal chalcogenide layer comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

13 . The method of claim 10 , further comprising forming a fourth metal chalcogenide layer adjacent to the third metal chalcogenide layer before forming the second metal chalcogenide layer, wherein the fourth metal chalcogenide layer has a bandgap different from the third bandgap and the second bandgap.

14 . The method of claim 13 , wherein the fourth metal chalcogenide layer comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

15 . The method of claim 13 , further comprising forming a fifth metal chalcogenide layer adjacent to the fourth metal chalcogenide layer before forming the second metal chalcogenide layer, wherein the fifth metal chalcogenide layer has a bandgap different from the fourth bandgap and the second bandgap.

16 . The method of claim 15 , wherein the fifth metal chalcogenide layer comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

17 . The method of claim 15 , further comprising forming a sixth metal chalcogenide layer adjacent to the fifth metal chalcogenide layer before forming the second metal chalcogenide layer, wherein the sixth metal chalcogenide layer has a bandgap different from the fifth bandgap and the second bandgap.

18 . The method of claim 17 , wherein the sixth metal chalcogenide layer comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

19 . The method of claim 17 , further comprising forming at least one additional metal chalcogenide layer adjacent to the sixth metal chalcogenide layer before forming the second metal chalcogenide layer, wherein the at least one additional metal chalcogenide layer has a bandgap different from the sixth bandgap and the second bandgap.

20 . The method of claim 19 , wherein the at least one additional metal chalcogenide layer comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

21 . The method of claim 1 , further comprising displacing one of the precursors with inert gas after pulsing the precursor.

22 . The method of claim 1 , further comprising heating the substrate before pulsing a precursor.

23 . The method of claim 22 , further comprising controlling the temperature based on the metal chalcogenide layer being formed.

24 . A structure, comprising

a substrate;

a conducting layer adjacent to the substrate;

a semiconductor absorber layer adjacent to the conducting layer, wherein the semiconductor absorber layer comprises copper, indium, gallium, selenium and/or sulfur; and

a buffer layer adjacent to the semiconductor absorber layer, wherein the buffer layer comprises a first metal chalcogenide layer adjacent to the semiconductor absorber layer and having a first bandgap and a second metal chalcogenide layer adjacent to the first metal chalcogenide layer and having a second bandgap.

25 . The structure of claim 24 , further comprising:

a semiconductor window layer adjacent to the buffer layer; and

a transparent conductive oxide layer adjacent to the semiconductor window layer.

26 . The structure of claim 24 , wherein each of the first and second metal chalcogenide layers comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

27 . The structure of claim 24 , wherein each of the first and second metal chalcogenide layers comprises one or more metal chalcogenide monolayers formed by pulsing a metal precursor and pulsing a chalcogen precursor.

28 . The structure of claim 24 , further comprising a third metal chalcogenide layer between the first metal chalcogenide layer and the second metal chalcogenide layer, wherein the third metal chalcogenide layer has a bandgap different from the first bandgap and the second bandgap.

29 . The structure of claim 28 , wherein the third metal chalcogenide layer comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

30 . The structure of claim 28 , further comprising a fourth metal chalcogenide layer between the third metal chalcogenide layer and the second metal chalcogenide layer, wherein the fourth metal chalcogenide layer has a bandgap different from the third bandgap and the second bandgap.

31 . The structure of claim 30 , wherein the fourth metal chalcogenide layer comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

32 . The structure of claim 30 , further comprising a fifth metal chalcogenide layer between the fourth metal chalcogenide layer and the second metal chalcogenide layer, wherein the fifth metal chalcogenide layer has a bandgap different from the fourth bandgap and the second bandgap.

33 . The structure of claim 32 , wherein the fifth metal chalcogenide layer comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

34 . The structure of claim 32 , further comprising a sixth metal chalcogenide layer between the fifth metal chalcogenide layer and the second metal chalcogenide layer, wherein the sixth metal chalcogenide layer has a bandgap different from the fifth bandgap and the second bandgap.

35 . The structure of claim 34 , wherein the sixth metal chalcogenide layer comprises a material selected from the group consisting of indium sulfide, indium selenide, indium oxide, zinc sulfide, zinc selenide, and zinc oxide.

36 . The structure of claim 24 , wherein the first metal chalcogenide layer comprises indium and the second metal chalcogenide layer comprises zinc.

37 . The structure of claim 24 , wherein the first metal chalcogenide layer comprises zinc and the second metal chalcogenide layer comprises indium

38 . The structure of claim 24 , wherein the buffer layer comprises a plurality of metal chalcogenide layers between the first metal chalcogenide layer and the second metal chalcogenide layer.