Multiple band gapped cadmium telluride photovoltaic devices and process for making the same
View Patent ↗A heterojunction photovoltaic device for the production of electrical energy in response to the incident light includes an optically transparent substrate, a front contact formed of an transparent conductive oxide for collecting light generated charge carriers, an n-type window layer formed of cadmium sulfide or zinc sulfide, a p-type absorber structure disposed on the window layer, thereby forming a rectification junction therebetween, and a back contact comprising at least one metal layer. The p-type absorber structure has a plurality of p-type absorber layers in contiguous contact. Each absorber layer contains cadmium as a principal constituent and has a different composition and a different band gap energy. The first absorber layer is in contiguous contact with the n-type window layer. The band gap energy progressively decreases from the first absorber layer to the last absorber layer in the p-type absorber structure.
1. A heterojunction photovoltaic device comprising:
an optically transparent substrate for receiving incident light;
a front contact formed of a transparent conductive oxide disposed on the side of said optically transparent substrate opposite incident light;
an n-type window layer having a band gap energy of at least 2.2 eV disposed on said front contact;
a p-type absorber structure deposited contiguously onto said n-type window layer, wherein said p-type absorber structure comprises three absorber layers in sequential touching contact, a first absorber of said three absorber layers is selected from the group consisting of CdSe, Cd 1-y Mg y Te, Cd 1-y Mn y Te and Cd 1-y Zn y Te, where y ranges from about 0.05 to about 0.20, a second absorber layer of said three absorber layers is CdTe and a third absorber layer of said three absorber layers is Cd 1-z Hg z Te, where z ranges from about 0.15 to about 0.20, the first absorber layer is in contiguous contact with said n-type window layer, the band gap energy progressively decreases from the first absorber layer to the last absorber layer; and
a back contact formed on the last absorber layer of said p-type absorber structure.
2. The photovoltaic device of claim 1 wherein said n-type window layer is CdS or Cd 1-x Zn x S, where x ranges from more than zero to no more than one.
3. The photovoltaic device of claim 1 wherein said front contact is aluminum doped zinc oxide or fluorine doped tin oxide.
4. The photovoltaic device of claim 1 further comprising a secondary transparent conductive oxide layer interposed between said front contact and said n-type window layer, wherein said secondary transparent conductive oxide layer is selected from the group consisting of zinc stannate, zinc oxide and tin oxide.
5. The photovoltaic device of claim 1 wherein said back contact comprises a first layer of copper in contiguous contact with said third absorber layer of said p-type absorber structure and having a layer thickness of not more than 7 nm and a second layer of a conductive metal disposed thereon, said conductive metal is nickel or gold.
6. The photovoltaic device of claim 1 wherein said back contact comprises a first layer of copper doped zinc telluride in contiguous contact with the third absorber layer of said p-type absorber structure and a second layer of titanium deposited on said first layer of copper doped zinc telluride.