Method for patterning Mo layer in a photovoltaic device comprising CIGS material using an etch process

#The present invention relates generally to photovoltaic devices, and more particularly to a method for etching a Mo layer in a photovoltaic device comprising CIGS material.

#Thin layers of material comprising Cu(In,Ga)Se, i.e. CIGS, are known to exhibit the highest photovoltaic conversion efficiency of any thin film material for a photovoltaic device (19.5%). See K. Ramanathan et al., “Properties of High-Efficiency CIGS Thin-Film Solar Cells,” 31st IEEE Photovoltaics Specialists Conference and Exhibition, Lake Buena Vista, Fla., Jan. 3-7, 2005; and D. E. Tarrant et al., “CIS thin film development and product status at Shell Solar, May 2003,” Proc. of 3rd WCPEC, Osaka, Japan, May 2003. Similar progress has been reported in the manufacturing area, where the efficiency of champion modules has exceeded 13% with yield above 80%. See M. Contreras et al., “High Efficiency Cu(In,Ga)Se2-Based Solar Cells: Processing of Novel Absorber Structures,” Proc. of 1st WCPEC, Hi., Dec. 5-9, 1994. Consequently, CIGS is considered by many in the art to be an attractive material for use in the manufacture of thin film photovoltaic panels.

#In a typical solar cell module, as shown in FIG. 1A, a CIGS layer 106 is grown to a thickness of about 2 μm on an underlying metal layer 104 comprised of molybdenum (Mo). Mo provides good ohmic contact and has a similar thermal coefficient of expansion as CIGS, which can be important for the elevated temperature of CIGS processing. The Mo is usually deposited on a substrate material 102 which may be, for example, glass, stainless steel, or plastic. A range of concentrations of Cu, In, Ga and Se can be used in the CIGS layer, and sometimes the Ga is absent or S may be added. Accordingly, CIGS is used herein in its broadest possible meaning in the context of similar or related films. Moreover, other materials may be used in thin film photovoltaic modules, either individually or in combination, and either alternatively or additionally. These include CdTe, amorphous silicon (a:Si) and micro- or nano-crystal silicon (μc:Si). See generally, Y. Hamakawa (ed.), “Thin-Film Solar Cells,” Chapter 10 (2004), the contents of which are incorporated herein by reference.

#These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures, wherein:

#FIGS. 1A and 1B illustrate certain aspects of the processing of thin-film structures including CIGS and an underlying conductor;

#FIGS. 2A and 2B illustrate an example process of etching a Mo/MoSe2 material in accordance with one embodiment of the invention; and

#The present invention will now be described in detail with reference to the drawings, which are provided as illustrative examples of the invention so as to enable those skilled in the art to practice the invention. Notably, the figures and examples below are not meant to limit the scope of the present invention to a single embodiment, but other embodiments are possible by way of interchange of some or all of the described or illustrated elements. Moreover, where certain elements of the present invention can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present invention will be described, and detailed descriptions of other portions of such known components will be omitted so as not to obscure the invention. In the present specification, an embodiment showing a singular component should not be considered limiting; rather, the invention is intended to encompass other embodiments including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present invention encompasses present and future known equivalents to the known components referred to herein by way of illustration.

#Generally, the present inventors have discovered several etch solutions that can effectively etch through Mo and/or MoSe2, and particularly when such materials are patterned during photolithographic processing with other materials such as CIGS in a thin film photovoltaic device.

#FIGS. 2A and 2B illustrate a first example embodiment for patterning Mo and/or MoSe2 in accordance with the invention. In this example, an etch system comprising a 1:1 combination of H2O2 and NH4(OH) is prepared for use. It should be noted that the below described drawings are not to scale, and relative dimensions of various layers and features will be specified in the descriptions where examples are appropriate. The drawings are intended for illumination rather than limitation.