TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The substrate is selected from soda lime glass, aluminum, stainless steel, titanium, molybdenum, steel, polyimide, Teflon (RTM: polytetrafluoroethylene), and brass, stainless steel/SiO2 and stainless steel/Si3N4. The metal ions comprises at least one of molybdenum ions, zinc ions, chromium ions, copper ions, titanium ions, silver ions, palladium ions, nickel ions, indium ions, gold ions, gallium ions, tin ions, cadmium ions, and germanium ions. The molar ratio of the metal ions to selenium ions is 0.05-1.0. Preferred Method: The electroplating temperature is 15-28 degrees C. The step of thermally treatmenting the electroplated stack to form a semiconductor compound is performed at a temperature of 40-70 degrees C at atmosphere comprising at least one of sulfur gas, nitrogen gas and argon gas. The step of measuring and controlling thickness of each stack layer is performed in systems comprising of a drying unit, a travelable XRF measurement unit, and a controlling unit.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred System: In the system, there is a hot gas zone where the water on electroplated stack is removed before going to travelable XRF measurement system for thickness measurement. A XRF or multiple XRFs is or are moved at same speed with the measuring target of the substrate during the measurement. The measured result from the travelable XRF measurement unit is sent to the controlling unit where the parameters such as electroplating current, temperature, solution composition, and substrate moving speed are adjusted based on the XRF measurement result until the thickness of the electroplated stack meet the target.    TECHNOLOGY FOCUS - METALLURGY - Preferred Components: The back contact electrode is one of the materials selected from Ti-Cu alloy, Cr-Cu alloy, W-Cu alloy, Mo-Cu alloy, Mo, W, Ti-W alloy, Ti/Pd, Ti/Pt, Mo/Cu, Cr/Pd, Ti/Ag, Ti/Cu, Cr/Cu, SiO2/Mo, Si3N4/Mo, and Ti/Au. The sequentially electroplated stack on the back contact electrode is selected from Cu/In/Ga-Se/Se-alloy, Cu/Ga-Se/In/Se-alloy, Cu/In/Cu/Ga-Se/Se-alloy, Cu/Se-alloy/In/Ga-Se, Cu/Se-alloy/Ga-Se/In, In/Cu/Ga-Se/Se-alloy, In/Ga-Se/Cu/Se-alloy, In/Se-alloy/Cu/Ga-Se, In/Se-alloy/Ga-Se/Cu, Ga-Se/Cu/In/Se-alloy, Ga-Se/In/Cu/Se-alloy, Ga-Se/Se-alloy/Cu/In, Ga-Se/Se-alloy/In/Cu, Se-alloy/Cu/In/Ga-Se, Se-alloy/In/Cu/Ga-Se, Se-alloy/Ga-Se/In/Cu, Se-alloy/In/Ga-Se/Cu, Cu/In/Ga-Se-Cu/Se-alloy, Cu/Ga-Se-Cu/In/Se-alloy, Cu/Se-alloy/In/Ga-Se-Cu, Cu/Se-alloy/Ga-Se-Cu/In, In/Cu/Ga-Se-Cu/Se-alloy, In/Ga-Se-Cu/Cu/Se-alloy, In/Se-alloy/Cu/Ga-Se-Cu, In/Se-alloy/Ga-Se-Cu/Cu, Ga-Se-Cu/In/Cu/Se-alloy, Ga-Se-Cu/Cu/In/Se-alloy, Ga-Se-Cu/Se-alloy/In/Cu, Ga-Se-Cu/Se-alloy/Cu/In, Se-alloy/In/Ga-Se-Cu/Cu, Se-alloy/Ga-Se-Cu/In/Cu, Se-alloy/Cu/In/Ga-Se-Cu, Se-alloy/Cu/Ga-Se-Cu/In. The Se-alloy is selected from Se-Ge alloy, Se-Pb alloy, Se-Fe alloy, Se-Ni alloy, Se-Cu alloy, Se-Pt alloy, Se-In alloy, Se-Pd alloy, Se-Ga alloy, Se-Ag alloy, Se-Ti alloy, Se-Cr alloy, and Se-Zn alloy. Preferred Method: The Ga-Se alloy is electroplated in an aqueous solution comprising of gallium ions, selenium ions and a complexing agent, where the gallium ions is formed by adding at least one of the gallium salts to the aqueous solution consisting of gallium chloride, gallium nitride, gallium sulfate, gallium acetate and gallium nitrate, the gallium ions concentration is 0.1-3.0 M, the selenium ions is formed by adding at least one of the compounds to the solution consisting of selenium acid (H2SeO4), selenous acid (H2SeO3), selenium dioxide (SeO2), and selenium trioxide (SeO3), the selenium ions concentration is 0.05-0.2M, the complexing agent is at least one of glucoheptonic acid sodium salt (C7H13NaO8), polyethylene glycol (C2H4O)nH2O, sodium lauryl sulfate (C12H25SO4Na), sodium ascorbate (C6H7O6Na), sodium salicylic (C7H5NaO3) and glycine (C2H5NO2) and the pH of the solution is 10-14. The Ga-Se-Cu alloy is electroplated in an aqueous solution comprising of gallium ions, selenium ions, copper ions, and a complexing agent selected from glucoheptonic acid sodium salt (C7H13NaO8), polyethylene glycol (C2H4O)nH2O, sodium lauryl sulfate (C12H25SO4Na), sodium ascorbate (C6H7O6Na), sodium salicylic (C7H5NaO3), and glycine (C2H5NO2). The Se-alloy is electroplated in an aqueous solution comprising of selenium ions, ions of at least one metal element, and at least one of the complexing agents, where the concentration of the selenium ions is 0.1-7.0 M and the complexing agent is at least one of glucoheptonic acid sodium salt (C7H13O8Na), polyethylene glycol (C2H4O)nH2O, sodium lauryl sulfate (C12H25SO4Na), sodium ascorbate (C6H7O6Na), sodium tartrate (Na2C4H4O6), glycine (C2H5NO2), sodium citrate (Na3C6H5O7.2H2O), and sodium salicylate (C7H5NaO3), the pH of the solution is 0.5-11.5, and temperature of the solution is 10-50 degrees C. EXAMPLE - An aqueous electroplating bath consisting of 2 M SeO2, 0.05 M CuCl2, and 0.1 M glucoheptonic acid sodium salt (C7H13NaO8) was used. The current density was at 15 mA/cm2 and 50 mA/cm2. The temperature was at 15 degrees C, 20 degrees C and 25 degrees C respectively. The pH was 1.75, 8.5 and 11.5 respectively. The anode used for the electroplating was a stainless steel plate. Substrates with indium, copper and gallium on the top surface were being electroplated and were used for the experimental as: stainless steel/Mo/Cu, stainless steel/Mo/Cu/In, stainless steel/Mo/Cu/In/Ga, stainless steel/Mo/Cu/Ga-Se, stainless steel/Si3N4/Mo/Cu, and soda lime glass/Mo/Cu/In/Ga. For stainless steel/Si3N4/Mo/Cu, the Si3N4 was patterned with partially opening so that the Mo was directly contacted with stainless steel through the opening areas. The Se-Cu alloy was electrodeposited on the above substrates. The results showed that no any interrupt was found with the Se-Cu thickness up to 10 mu m. The maximum current density was 50 mA/cm2. It was found that the electrodeposited Se-Cu layer had dense surface on indium and gallium surface than on copper surface.