Mixed ternary heterojunction solar cell
AssigneeThe Boeing Company
InventorsWen S. Chen, John M. Stewart
Life of this patent
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Abstract
A thin film heterojunction solar cell and a method of making it has a p-type layer of mixed ternary I-III-VI.sub.2 semiconductor material in contact with an n-type layer of mixed binary II-VI semiconductor material. The p-type semiconductor material includes a low resistivity copper-rich region adjacent the back metal contact of the cell and a composition gradient providing a minority carrier mirror that improves the photovoltaic performance of the cell. The p-type semiconductor material preferably is CuInGaSe.sub.2 or CuIn(SSe).sub.2.
Claims92
A thin film polycrystalline heterojunction solar cell, comprising:
- a back metal contact;
- a p-type layer on the contact comprising a mixed ternary, I-III-VI.sub.2 polycrystalline semiconductor material having a composition gradient in the direction of the thickness of the layer to form a minority carrier mirror within the layer, the layer having low resistivity region adjacent the back metal contact;
- an n-type layer of semiconductor material on the p-type layer to form a photovoltaically active heterojunction;
- and
- electrically conductive means on the n-type layer.
A thin film polycrystalline heterojunction solar cell comprising:
- a conductive metal layer
- a p-type layer of CuIn.sub.l-x Ga.sub.x Se.sub.2 semiconductor material on said conductive metal layer, wherein x is in the range of from 0 to 0.3, having a composition gradient of Cu and In in the direction of thickness and having a low resistivity Cu-rich region adjacent the conductive metal layer and a relatively Cu-poor region adjacent the junction;
- an n-type layer of CdZnS semiconductor material on said p-type material to form a photovoltaically active junction;
- an electrically conductive top contact on one surface of the n-type layer;
- and
- at least one anti-reflective coating over the top contact.
A method of making on a substrate a thin film polycrystalline heterojunction solar cell comprised of a conductive metal layer;
- a p-type layer of polycrystalline, mixed ternary I-III-VI.sub.2 material material having a low resistivity Cu-rich region adjacent said conductive metal layer, a higher bandgap region, within said Cu-rich region, and a lower bandgap region, the higher and lower bandgap regions defining a minority carrier mirror;
- a layer of polycrystalline n-type semiconductor material disposed on the p-type layer defining the heterojunction;
- and an electrically conductive means disposed on said n-type material, said method comprising the steps of:
- (a) introducing vapors of the elements from Groups I, III, and VI simultaneously into a vessel to form a vapor mixture comprising the components of the p-type layer;
- (b) independently controlling the vaporization rate of the elements;
- (c) depositing said vapor mixture on a substrate to form a p-type polycrystalline film of mixed ternary I-III-VI.sub.2 material having a copper-rich region and a minority carrier mirror;
- (d) depositing the n-type semiconductor material on said p-type material;
- and
- (e) depositing an electrically conductive means on the surface of the n-type semiconductor material.
A thin film polycrystalline heterojunction solar;
- cell, comprising:
- a conductive metal layer;
- a p-type layer of polycrystalline CuInS.sub.2x Se.sub.2(l-x) semiconductor material on the conductive metal layer, wherein x is in the range of from 0 to 1.0, the layer having a composition gradient of S in the direction of the thickness of the layer to form a minority carrier mirror and having low resistivity Cu-rich region adjacent the conductive material layer;
- an n-type layer of semiconductor material on the p-type layer to form a photoactive heterojunction;
- and
- electrically conductive means on the n-type layer.
A method of making a thin film polycrystalline heterojunction solar cell on a substrate comprised of a conductive metal layer;
- a p-type layer of polycrystalline CuIn.sub.l-x Ga.sub.x Se.sub.2, wherein x is in the range from about 0 to 1.0, the layer having a low resistivity Cu-rich region adjacent said conductive metal layer, a Ga-rich higher bandgap region within said Cu-rich region, and a lower bandgap region adjacent to said Ga-rich region;
- a layer of polycrystalline n-type semiconductor material disposed on the p-type layer to form the heterojunction;
- and an electrically conductive means disposed on the n-type material, said method comprising the steps of:
- (a) introducing a vapor of copper to a vessel containing said substrate while simultaneously introducing vapors of gallium, indium, and selenium to form a vapor mixture comprising the components of said p-type layer;
- (b) controlling the temperature of said substrate;
- (c) independently controlling the vaporization rates of copper, indium, gallium, and selenium;
- (d) maintaining the temperature of said substrate at a first temperature while depositing said vapor mixture on said substrate to form said Cu-rich region of said p-type material;
- (e) raising the temperature of said substrate to a second temperature and decreasing the Ga/In ratio by decreasing the vaporization rate of gallium;
- (f) decreasing the amount of copper in the vapor mixture by decreasing the vaporization rate of copper;
- (g) continuing depositing at the new vaporization rates to form a film having the above recited composition profile;
- (h) depositing the n-type layer on said p-type layer;
- and
- (i) depositing an electrically conductive means on the surface of said n-type layer.
A method for making a mixed ternary, I-III-VI thin film semiconductor, comprising the steps of:
- (a) heating a substrate having a back metal contact on an exposed surface to a temperature of about 450.degree. C. in a high vacuum chamber;
- (b) introducing simultaneously a mixed vapor of the preferred elements of Groups I, III, and VI into the vessel at predetermined fluxes for each element;
- (c) depositing a first region on the contact for a predetermined time to form a mixed ternary polycrystalline material;
- (d) altering at least one flux of the elements while increasing the substrate temperature to about 550.degree. C;
- and
- (e) depositing for a predetermined time a second region over the first region to complete the film, the second region being a mixed ternary polycrystalline material having a different chemical composition from the composition of the first region.
A mixed ternary, I-III-VI.sub.2 thin film semiconductor comprising:
- (a) a copper-rich region of CuInGaSe.sub.2 ;
- and
- (b) a copper-deficient region of CuInGaSe.sub.2 overlying the copper-rich region.
The semiconductor of cliam 55 wherein the gallium-rich region and gallium-deficient region define a minority carrier mirror in the I-III-VI.sub.2 semiconductor formed by the change in composition of the semiconductor from a higher bandgap material to a lower bandgap material.
A mixed ternary, copper indium gallium selenide material for use in a I-III-VI.sub.2 /II-VI heterojunction solar cell, comprising:
- (a) a low resistivity relatively high conductivity thin film region positionable adjacent a back metal contact in the cell and having a composition simultaneously rich in copper and gallium;
- and
- (b) a second thin film region overlying and forming an interface with the low resistivity thin film region and positionable adjacent the junction in the cell, the second thin film region having a composition simultaneously deficient in copper and gallium.
A solar cell including the material of cliam 77.
The material of cliam 72 wherein the II-VI thin film is a mixed binary semiconductor.
A mixed ternary copper indium gallium selenide material for use in a I-III-VI.sub.2 /II-VI heterojunction solar cell, comprising:
- a constant gallium concentration, polycrystalline material having a low resistivity, copper-rich region positionable adjacent a back metal contact in the cell and having a copper-deficient region overlying the copper-rich region and positionable adjacent the junction of the cell,
- wherein 0.25.ltoreq.the mole fraction of gallium.ltoreq.0.35.
A thin film polycrystalline heterojunction solar cell, comprising:
- (a) a substrate;
- (b) a base contact on one surface of the substrate;
- (c) a mixed ternary CuIn.sub.l-x Ga.sub.x Se.sub.2 l p-type semiconductor layer deposited on the base contact and including,
- (i) a first region adjacent the contact and being simultaneously rich in copper relative to the ratio of Ga and In and rich in Ga relative to In;
- (ii) a second region on the first region being simultaneously deficient in copper relative to the ratio of Ga and In and deficient in Ga relative to the first region, and having a bandgap lower than that of the first region;
- (d) a mixed ternary n-type semiconductor layer of Zn.sub.y Cd.sub.l-y S deposited on the second region of the p-type semiconductor to form a photoactive heterojunction the layer including,
- (i) an undoped region adjacent the heterojunction, and
- (ii) a low resistivity doped region overlying the undoped region and remote from the heterojunction;
- (e) a collector deposited on the n-type semiconductor layer remote from the heterojunction, comprising at least one layer of ZnO;
- and
- (f) an antireflection coating deposited over the collector,
- wherein 0<x<0.1 and 0<y<0.50.
Dependencies are inferred from the claim text.