NOVELTY - Preparing a selenium electroplating solution, comprises: forming the solution from a mixture comprising (a) selenium oxide, (b) an acid comprising alkane sulfonic acid, alkene sulfonic acid, aryl sulfonic acid, heterocyclic sulfonic acid, aromatic sulfonic acid or perchloric acid and (c) a solvent; and adjusting pH of the solution from 2 to 3.    USE - The methods are useful for: electroplating selenium; fabricating the photovoltaic device; and preparing selenium electroplating solution (claimed), which are used to form selenium alloy films including copper indium selenide, copper indium gallium selenide and copper zinc tin sulfide which serve as absorber layer in photovoltaic devices.    ADVANTAGE - The method: permits plating of selenium, and avoids the need for selenization; permits the selenium to be deposited as an interlayer in the stack, thus avoiding the problem of large volume expansion and loss of adhesion of the chalcopyrite material; allows a high rate of deposition; improves adhesion of the absorber layer to its back contact materials; and utilizes cheap evaporation or sputtering method for forming the absorber layer, thus is cost effective.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) a selenium electroplating solution, comprising: (a)-(c) as above per se; and a base, where the pH of the solution is 2-3;    (2) an electroplating method, comprising preparing the selenium electroplating solution, providing a substrate (302), and electroplating a selenium-containing film on the substrate using the solution as a plating bath; and    (3) fabricating a photovoltaic device (300), comprising: preparing the selenium electroplating solution comprising (a)-(c) as above per se, at least one metal salt and the base, where the pH of the solution is 2-3; providing a substrate; electroplating a selenium-containing absorber layer (304) on the substrate using the solution as a plating bath; forming a buffer layer (306) on the absorber layer; and forming a transparent electrode (308) on the buffer layer.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the photovoltaic device.    Photovoltaic device (300)    Substrate (302)    Absorber layer (304)    Buffer layer (306)    Transparent electrode (308)