Methods for forming thin-film heterojunction solar cells from I-III-VI.sub. 2

In a photovoltaic light-to-electrical energy transducer of the type including a thin-film A-B-type heterojunction where "A" and "B" are selected from the group of semiconductor materials consisting of:

• ______________________________________ A and B ______________________________________ (i) a p-type ternary material and an n-type material;
• (ii) an n-type ternary material and a p-type material;
• (iii) an n-type material and a p-type ternary material;
• (iv) a p-type material and an n-type ternary material;
• ______________________________________
• and wherein the transducer includes a substrate, a first contact deposited on said substrate, a first semiconductor layer formed of A-type material deposited on said first contact, a second semiconductor layer formed of B-type material deposited on said first semiconductor layer and defining therewith the thin-film A-B-type heterojunction, and a second contact deposited on said second semiconductor layer, the improvement comprising:
• (a) the one of said first and second semiconductor layers formed of a ternary semiconductor material comprising a semiconductor layer having been formed with two composition graded regions with one region superimposed on the other and with one region having a first preselected ratio of two of the elements in said ternary semiconductor material so as to form a low resistivity semiconductor region and the other of said regions having a different preselected ratio of the same two elements and having been formed as a high resistivity transient semiconductor region and with said two regions having been formed as a transient homojunction;
• and,
• (b) the other of said first and second semiconductor layers having been formed in face-to-face contact with said high resistivity transient semiconductor region of said transient homojunction so as to permit said high resistivity transient semiconductor region to evolve through elemental interdiffusion into a region of relatively high resistivity semiconductor material of the same type as said low resistivity region to thereby form a thin-film A-B-type heterojunction photovoltaic light-to-electrical energy transducer.

The method of forming a p-n-type heterojunction photovoltaic device comprising the steps of:

• (a) depositing a first region of relatively low resistivity p-type material on a metallized substrate;
• (b) depositing a second region of relatively high resistivity transient n-type material formed of the same elemental constituents as the relatively low resistivity p-type material deposited in step (a) with such transient n-type material being deposited on the first region of p-type material and defining therewith a transient p-n-type homojunction;
• and,
• (c) depositing a film of low resistivity n-type semiconductor material on the transient p-n-type homojunction formed in steps (a) and (b), whereupon interdiffusion of the constituent elements of the materials employed in steps (a), (b) and (c) between the p-type material and the transient n-type material, and between the transient n-type material and the n-type semiconductor material, causes the transient n-type material to evolve into relatively high resistivity p-type material so as to form a thin-film heterojunction essentially devoid of growth nodules and permitting a photovoltaic response characteristic of energy transducers capable of exhibiting relatively high conversion efficiencies at least approximating 10.0%.

In a method of forming a photovoltaic light-to-electrical energy transducer of the type comprising a thin-film p-n-type heterojunction including a metallized substrate, a first semiconductor layer formed of p-type semiconductor material and deposited on the metallized substrate, a second semiconductor layer formed of low resistivity n-type semiconductor material formed on the first semiconductor layer, and a grid-like upper contact formed on the second semiconductor layer, the improvement comprising a method wherein:

• (a) the first semiconductor layer of a ternary semiconductor material is formed by simultaneous elemental evaporation to form a first region of low resistivity p-type semiconductor material on the metallized substrate;
• and,
• (b) while the ternary material is undergoing simultaneous elemental evaporation the ratio of two of the elemental constituents being evaporated is adjusted so as to form a second region of relatively high resistivity transient n-type semiconductor material on the first region of low resistivity p-type material, thereby forming a transient p-n-type homojunction on the metallized substrate;
• and, wherein upon formation of the second semiconductor layer of n-type material on the transient p-n homojunction, the second region of relatively high resistivity transient n-type semiconductor material is sandwiched between the first region of low resistivity p-type material and the second semiconductor layer of low resistivity n-type material so as to permit the transient n-type region to evolve through elemental interdiffusion into a region of relatively high resistivity p-type material to thereby form a thin-film p-n-type heterojunction photovoltaic light-to-electrical energy transducer.

A p-n-type heterojunction photovoltaic device comprising, in combination:

• a metallized substrate;
• a first relatively thin-film region of relatively low resistivity p-type material adhered to said metallized substrate;
• a second relatively thin-film region formed of the same elemental constituents as said relatively low resistivity p-type material and having been formed as a relatively high resistivity transient n-type material region with said relatively low resistivity p-type material and said relatively high resistivity transient n-type material region having been formed as a composite transient p-n-type homojunction semiconductor layer;
• and, a relatively thin film of low resistivity n-type semiconductor material having been deposited on said transient p-n homojunction whereupon interdiffusion of the constituent elements of the materials defining said p-type region, said transient n-type region and said n-type semiconductor material between the p-type material and the transient n-type material, and between the transient n-type material and the n-type semiconductor material causes the transient n-type material to evolve into relatively high resistivity p-type material so as to form a thin-film heterojunction essentially devoid of growth nodules and permitting a photovoltaic response characteristic of energy transducers capable of exhibiting conversion efficiencies at least approximating 10.0%.

In a method of forming a photovoltaic light-to-electrical energy transducer of the type including a thin-film A-B-type heterojunction where "A" and "B" are selected from the group of semiconductor materials consisting of:

• ______________________________________ A and B ______________________________________ (i) a p-type ternary material and an n-type material;
• (ii) an n-type ternary material and a p-type material;
• (iii) an n-type material and a p-type ternary material;
• (iv) a p-type material and an n-type ternary material;
• ______________________________________
• and wherein the transducer includes a substrate, a first contact deposited on the substrate, a first semiconductor layer formed of A-type material deposited on the first contact, a second semiconductor layer formed of B-type material deposited on the first semiconductor layer and defining therewith the thin-film A-B-type heterojunction, and a second contact deposited on the second semiconductor layer, the improvement comprising a method wherein:
• (a) the one of the first and second semiconductor layers formed of a ternary semiconductor material is formed by simultaneous elemental evaporation of the ternary semiconductor material to form a semiconductor layer having two composition graded regions sequentially formed one upon the other with one region having a first preselected ratio of two of the elements in the ternary semiconductor material so as to form a low resistivity semiconductor region and the other of the regions having a different preselected ratio of the same two elements so as to form a high resistivity transient semiconductor region and with the two regions defining a transient homojunction;
• (b) the other of the first and second semiconductor layers is formed by deposition of a semiconductor material in face-to-face contact with respect to the high resistivity transient semiconductor region of the transient homojunction;
• and,
• (c) the energy transducer formed is heated subsequent to steps (a) and (b);
• to thereby form a transducer wherein the high resistivity transient semiconductor region formed in step (a) is permitted to evolve through elemental interdiffusion into a region of relatively high resistivity semiconductor material of the same type as the low resistivity region formed in step (a) so as to form a thin-film A-B-type heterojunction photovoltaic light-to-electrical energy transducer.

The method of forming a p-n-type heterojunction photovoltaic device comprising the steps of:

• (a) depositing a first region of relatively low resistivity p-type material on a metallized substrate;
• (b) depositing a second region of relatively high resistivity transient n-type material formed of the same elemental constituents as the relatively low resistivity p-type material deposited in step (a) with such transient n-type material being deposited on the first region of p-type material and defining therewith a transient p-n-type homojunction;
• (c) depositing a film of low resistivity n-type semiconductor material on the transient p-n-type homojunction formed in steps (a) and (b);
• and,
• (d) heating the p-n-type heterojunction photovoltaic device formed in steps (a), (b) and (c);
• whereupon interdiffusion of the constituent elements of the materials employed in steps (a), (b) and (c) between the p-type material and the transient n-type material, and between the transient n-type material and the n-type semiconductor material, causes the transient n-type material to evolve into relatively high resistivity p-type material so as to form a thin-film heterojunction essentially devoid of growth nodules and providing a photovoltaic response characteristic of energy transducers having relatively high conversion efficiencies.

The method of claim 127 wherein the II-VI material is selected from the group consisting of:

• CdS;
• Cd.sub.1-x Zn.sub.x S;
• and,
• CdS.sub.1-x Se.sub.x.

A thin-film A-B-type heterojunction photovoltaic device wherein "A" and "B" are selected from the group of semiconductor materials consisting of:

• ______________________________________ A AND B ______________________________________ (1) a p-type ternary material and an n-type material;
• (2) an n-type ternary material and a p-type material;
• (3) an n-type material and a p-type ternary material (4) a p-type material and an n-type ternary material;
• ______________________________________
• comprising a first semiconductor layer having been formed with a first region of A-type material and a second superimposed region of transient B-type material with said first and second regions initially defining a transient A-B-type homojunction, and a second semiconductor layer deposited on said first layer and formed of a second B-type material whereupon interdiffusion of the constituent elements defining:
• (i) said A-type material;
• (ii) said transient B-type material;
• and (iii), said second B-type material;
• causes the transient B-type material to evolve into A-type material so as to form a thin-film heterojunction permitting a photovoltaic response characteristic of an energy transducer capable of exhibiting a conversion efficiency approximating on the order of 10%.