TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Film: The film comprises substantially only a single chalcopyrite phase. Preferred Method: Preparation of the chalcopyrite film having the composition (I) for the photovoltaic device involves: (a) depositing onto a back contact of the substrate at least one film of elemental Ag, Tl, or Te, or their oxides, sulfides, selenides, or tellurides, and subsequently depositing at least one of Cu, In, Ga, Al, Se, or S, optionally at least one of Ag, Tl, or Te, and optionally further processing the film at a further elevated temperature in an inert or O-, S-, Se-, or Te-containing atmosphere to form the chalcopyrite film; (a1) sequentially co-evaporating Ag, Cu, In, Ga, and Se onto a heated substrate to form the chalcopyrite film; (a2) depositing at least one layer of Ag, Cu, In, Ga, and optionally Se, or their alloys or oxides, sulfides, or selenides, and subsequently processing the film at a further elevated temperature in an inert, O-, S-, or Se-containing atmosphere to form the chalcopyrite film; or (a3) depositing a particulate film comprising Ag, Cu, Tl, In, Ga, O, S, Se, and/or Te, or their alloys, oxides, sulfides, selenides, or tellurides, and subsequently processing the film at a further elevated temperature to form the chalcopyrite film. The step (a) involves depositing the at least one film of elemental Ag, Tl, or Te, or their oxide, sulfide, selenide, or tellurides via sputter deposition or via reactive sputter deposition in an oxygen-, sulfur-, selenium-, or tellurium-containing atmosphere; where either the sputtering targets used in forming the back contact and Ag-, Tl-, or Te- containing layers are in the same deposition chamber, and the substrate is first sputtered to form the back contact, and then coated by the Ag-, Tl-, or Te- containing layer; or involves sputtering an Ag film onto the back contact and subsequently forming the remainder of the chalcopyrite film by sequentially co-evaporating Cu, Ga, In, Se, and optionally additional Ag.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The substrate comprises a self-supporting polymer film (preferably self-supporting polyimide, liquid crystal polymer, or rigid-rod polymer film). GLASS AND CERAMICS -Preferred Components: The substrate comprises soda-lime glass. Preferred Definitions:    w=0.05-0.3;    x=0.15-0.5;    K'=Al;    Q'=S.    EXAMPLE - A chalcopyrite film for a photovoltaic device was formed as follows. A soda-lime glass substrate was sputtered with Mo to form a 700 nm Mo film to serve as the back contact. A 92 nm Ag film was deposited by evaporation directly onto the Mo back contact. Cu, In, Ga, and Se were then co-evaporated onto this structure at a substrate temperature of 525?OC to create a resultant homogenous Cu1-wAgwIn1-xGaxSe2 (where w=0.01-0.75; and x=0.1-0.8) film with thickness of 2 mu m, and atomic ratios of Ag/(Ag+Cu) of 0.3, Ga/(Ga+In) of 0.7, and (Ag+Cu)/(Ga+In) of 0.85. A control film was also produced, employing a stoichiometrically equivalent 64 nm Cu film in place of the 92 nm Ag film. The absorber layer film was then used in the fabrication of photovoltaic devices by chemical bath deposition of 50 nm CdS, followed by sputter deposition of a 200 nm ZnO:ITO (indium tin oxide) window layer, followed by e-beam deposition of a Ni-Al grid structure. Photovoltaic device performance of the photovoltaic devices formed with the test Ag-containing, and the control non-Ag-containing, was then evaluated. Comparison of photovoltaic device properties between Ag- and non-Ag- containing absorber films, by using 2 samples per absorber composition, 6 devices per sample, and 12 devices total per absorber composition for the test/control films were as follows: open-circuit voltage (Voc) (V) = 0.789 plus minus 0.005/0.79 plus minus 0.009; short-circuit current (Jsc) (mA/cm2) = 20.8 plus minus 1.3/16.8 plus minus 1.4; fill factor i.e. maximum power delivered by device) divide by (Jsc x Voc)) (FF) (%) = 64.4 plus minus 1.9/71.4 plus minus 1; and photovoltaic energy conversion efficiency (%) = 10.6 plus minus 0.8/9 plus minus 2. A further performance improvement achieved by an Ag-containing film versus the non-Ag-containing film was also evaluated, in which test Ag-containing device showed significantly improved current collection compared with that of the non-Ag-containing film, near the high-wavelength band edge. An improved spectral response of the Ag0.3Cu0.7Ga0.7In0.3Se2 absorber layer compared with CuGa0.7In0.3Se2 was also observed. The curve labeled (Ag-Cu)/Cu showed the fractional enhancement into current collection obtained by the incorporation of Ag, demonstrating significant improvement at the high-wavelength band edge. The device had a quantum efficiency at 860 nm that is ( greater than or equal to 20, preferably greater than or equal to 40, especially greater than or equal to 60, particularly 70)% greater than that of an equivalent device employing an equivalent film that contains no Ag.