Hazy Zinc Oxide Film for Shaped CIGS/CIS Solar Cells
A method for fabricating a shaped thin film photovoltaic device includes providing a length of tubular glass substrate having an inner diameter, an outer diameter, a circumferential outer surface region covered by an absorber layer and a window buffer layer overlying the absorber layer. The substrate is placed in a vacuum of between about 0.1 Torr to about 0.02 Torr and a mixture of reactant species derived from diethylzinc species, water species, and a carrier gas are introduced, as well as a diborane species. The substrate is heated to form a zinc oxide film with a thickness of 0.75-3 μm, a haziness of at least 5%, and an electrical resistivity of less than about 2.5 milliohm-cm.
1 . A method for fabricating a shaped thin film photovoltaic device, the method comprising:
providing a length of tubular glass substrate having an inner diameter, an outer diameter, a circumferential outer surface region covered by an absorber layer and a window buffer layer overlying the absorber layer;
subjecting the tubular glass substrate in a vacuum environment of between about 0.1 Torr to about 0.02 Torr;
introducing a mixture of reactant species derived from diethylzinc species, water species, and a carrier gas to the vacuum environment;
introducing a diborane species into the mixture of reactant species;
heating tubular glass substrate; and
forming a zinc oxide film overlying the window buffer layer, the zinc oxide film having a thickness of 0.75-3 μm, a haziness of at least 5%, and an electrical resistivity of less than about 2.5 milliohm-cm.
2 . The method of claim 1 wherein the zinc oxide film further is characterized by an average grain size of about 3000 Angstroms to about 5000 Angstroms.
3 . The method of claim 1 wherein the diethylzinc species comprises dielethyl vapor.
4 . The method of claim 1 wherein the water species comprises water vapor.
5 . The method of claim 1 wherein the carrier gas comprises an inert gas.
6 . The method of claim 1 wherein the reactant species has a water-to-diethylzinc ratio between about 1 and about 4.
7 . The method of claim 1 wherein the diborane to diethylzinc ratio is from about zero to about five percent.
8 . The method of claim 1 wherein introducing the diborane species using a selected flow rate comprises controlling diborane to diethylzinc ratio to about one percent.
9 . The method of claim 1 wherein the tubular glass substrate is heated to a temperature range from about 130 degrees Celsius to about 190 degrees Celsius.
10 . The method of claim 1 wherein the tubular glass substrate is maintained at a temperature greater than about 200 degrees Celsius.
11 . The method of claim 1 wherein transferring an amount of thermal energy comprises resistive heating of the heating rod.
12 . The method of claim 1 wherein the heating rod comprises a spindle carrying running hot fluid and an inflatable surface configured to, after being inserted, make intimate contact with an inner surface of the tubular glass substrate.
13 . The method of claim 1 wherein the zinc oxide film with the haziness of about 5% and greater has a total optical transmission rate of 90 percent and greater.
14 . The method of claim 1 wherein the zinc oxide film with the haziness of about 5% and greater has a transmission rate of 80 percent and greater for electromagnetic radiation having a wavelength of about 800 nanometers to about 1200 nanometers.
15 . The method of claim 1 wherein introducing a mixture of reactant species increases a pressure of the chamber to about 0.5 to 1 Torr.
16 . The method of claim 1 wherein the absorber layer comprises a CIGS material or a CIG material.
17 . The method of claim 1 wherein the window buffer layer comprises a cadmium sulfide material.
18 . A method for forming a thin film photovoltaic device, the method comprising:
providing a shaped substrate member including a surface region;
forming a first electrode layer overlying the surface region;
forming an absorber material comprising a copper species, an indium species, and a selenide species overlying the first electrode layer;
forming a window buffer layer comprising a cadmium selenide species overlying the absorber material; and
forming a zinc oxide layer of about 0.75 to 3 microns in thickness overlying the window buffer layer using one or more precursor gases including a zinc species and an oxygen species and an inert carrier gas;
wherein the shaped substrate member is maintained at a temperature of greater than about 130 degrees Celsius substantially uniformly throughout the surface region during a chemical reaction of the one or more precursor gases thereon and extended annealing of the zinc oxide layer, thereby leading to a hazy surface optical characteristics and a bulk grain size of about 3000 Angstroms to about 5000 Angstroms within the zinc oxide layer.
19 . The method of claim 18 wherein the hazy surface optical characteristics comprises a ratio about 5% and greater of a scattered component of transmitted light to the total amount of light transmitted through the zinc oxide layer.
20 . The method of claim 18 wherein the chemical reaction of the one or more precursor gases occurs with at least a dopant gas comprising boron species being added at a preselected flow rate.
21 . The method of claim 20 wherein the added boron species causes the zinc oxide layer to have a sheet resistivity of about 2.5 milliohm-cm and less.
22 . The method of claim 20 wherein the chemical reaction is a deposition process based on Metal-Organic Chemical Vapor Deposition technique.
23 . A structure for thin-film photovoltaic device, the structure comprising:
a shaped substrate member including a surface region;
a first electrode film overlying the surface region;
an absorber material comprising a copper species, an indium species, and a selenide species overlying the first electrode film;
a window buffer layer comprising a cadmium selenide species overlying the absorber material; and
a zinc oxide film of about 0.75 to 3 microns in thickness overlying the window buffer layer, the zinc oxide film being characterized by a thickness from 0.75-3 μm, a haziness of 5% and greater, and an electrical resistivity of about 2.5 milliohm-cm and less;
wherein the zinc oxide film is formed via extended annealing of the shaped substrate member at a temperature greater than about 130 degrees Celsius substantially uniformly throughout the surface region within an ambient of precursor gases including a zinc species, an oxygen species, and an inert carrier gas.
24 . The structure of claim 23 wherein the zinc oxide film further is characterized by an average grain size of about 3000 Angstroms to about 5000 Angstroms.
25 . The structure of claim 23 wherein the shaped substrate member comprises a glass.
26 . The structure of claim 23 wherein the precursor gases comprise diethylzinc species, water species, and an inert gas.
27 . The structure of claim 23 wherein the zinc oxide film characterized by the haziness of about 5% and greater has a total optical transmission rate of at least 90 percent.