Formation of CIGS Absorber Layers on Foil Substrates
An absorber layer of a photovoltaic device may be formed on an aluminum or metallized polymer foil substrate. A nascent absorber layer containing one or more elements of group IB and one or more elements of group IIIA is formed on the substrate. The nascent absorber layer and/or substrate is then rapidly heated from an ambient temperature to an average plateau temperature range of between about 200° C. and about 600° C. and maintained in the average plateau temperature range 2 to 30 minutes after which the temperature is reduced.
1 . A method for forming an absorber layer of a photovoltaic device, comprising the steps of:
providing a substrate comprising at least one electrically conductive aluminum foil substrate ( 102 ), at least one interface layer ( 103 ) including at least one material selected from the group consisting of a carbide, an oxide, a nitride, tantalum nitride, tungsten nitride and silicon nitride, and at least one electrically conductive base electrode layer ( 104 ) comprising a layer of molybdenum, wherein the interface layer is positioned between the aluminum foil substrate and the base electrode layer and wherein the interface layer acts as a diffusion barrier to inhibit inter-diffusion of molybdenum in the electrode and aluminum in the substrate during heating, and
forming a nascent absorber layer ( 106 ) containing one or more elements of group IB, IIIA and VIA on the aluminum foil substrate characterized by:
depositing the nascent absorber layer from a solution of nanoparticulate precursor materials;
annealing the deposited nascent absorber layer and/or substrate by:
rapidly heating the nascent layer and/or substrate from an ambient temperature to a plateau temperature range of between 200° C. and 600° C. at a rate of between 5° C./sec and 150° C./sec;
maintaining the absorber layer and/or substrate in the plateau temperature range for between 2 minutes and 30 minutes; and
reducing the temperature of the absorber layer and/or substrate; and
incorporating one or more group VIA elements into the absorber layer in a second or later annealing stage.
2 . The method of claim 1 wherein the one or more group VIA elements include selenium.
3 . The method of claim 1 wherein the one or more group VIA elements include sulfur.
4 . The method of claim 1 wherein rapidly heating the nascent absorber layer and/or substrate is performed by radiant heating of the nascent absorber layer and/or substrate.
5 . The method of claim 4 wherein one or more infrared lamps apply the radiant heating.
6 . The method of claim 1 wherein the steps of forming and rapidly heating the nascent absorber layer take place as the substrate passes through roll-to-roll processing.
7 . The method of claim 1 wherein the aluminum foil substrate has a thickness of at least about 5 microns or more.
8 . The method of claim 1 wherein said annealing stages are either discrete or continuous.