NOVELTY - Forming active layer coating involves: forming molten mixture of at least one metal of group IIIA and metallic nanoparticles containing elements of group IB; and coating substrate (202) with film formed from molten mixture.    USE - For forming active layer coating, useful for forming active layer of photovoltaic cell (claimed) such as CI(G)S (copper, indium, gallium and sulfur) thin-film solar cells.    ADVANTAGE - The method provides improved method for forming active layer coating of photovoltaic cell, such that metallic components of IB-IIIA-VIA photovoltaic cell active layer can be directly coated onto substrate by using relatively low melting point (e.g. less than 500 degrees C) metals such as indium and gallium. By the method, the CI(G)S (copper, indium, gallium and sulfur) thin-film solar cells may be efficiently and reproducibly fabricated directly from a metallic solution by blending at least one molten group IIIA metal with solid nanoparticles containing group IB and (optionally) group IIIA metals. The molten mixture may be coated onto a thin film substrate in the molten state e.g. using coating techniques such as hot-dipping, hot microgravure and/or air-knife coating. After coating, the substrate may be cooled and annealed in sulfur-containing or selenium-containing atmosphere. Whereas recently, solar cells fabricated from alloys of Cu and In with Se or S have been developed by sputtering, evaporation, and chemical vapor deposition. However, vacuum-based deposition systems such as sputtering and evaporation can only control stoichiometric ratio of co-deposited materials with high-cost, and low-speed processes. This limitation severely impacts production of solar cells where active layer composition must be tightly controlled e.g. synthesis of high-performance CIGS active layer is only possible within narrow ratio of copper to indium and/or gallium. Co-evaporation or co-sputtering of individual CIGS elements requires controlled coordination of deposition rates in manner that is uniform both spatially across a substrate and from run to run. It is difficult to deposit uniform films on large areas using coincident vapor phase processes. Furthermore, deposition processes such as sputtering and evaporation typically result in less efficient materials utilization, as deposited material is also transported from the source target to chamber walls or shields rather than just substrate. The molten mixture includes low-melting point metal of group IB (e.g. indium and/or gallium) and nanoparticles containing elements of group IIIA and/or IB e.g. copper and gallium e.g. (1 nm to 1 micron, preferably 1-100 nm, especially 1-40 nm). The decreased particle size can significantly lower both the melting point and sintering temperature required. By appropriately adjusting particle size distribution amongst particles of different materials in the mixture, it is possible for all particles to melt at about same temperature during sintering and yield more uniform crystalline phases. This enhances electronic properties of crystals in resulting CIGS film. By contrast, in prior art, CuInSe2 powders generated e.g. by milling or nebulizing process to create powder precursors have contained mixture of both small and large particles, resulting in a relatively broad size distribution. The presence of such a broad size distribution results in poor film formation. The improved method provides low-cost, high-volume production of large area photovoltaic devices. Further, in contrast to prior solution-based approaches that have focused on lower temperature CIGS processing, the method utilizes higher-temperature CIGS processing e.g. 150-250 degrees C, with hot-melt coating equipment, and enables direct deposition of thin film from molten metallic paste. The method is also compatible with roll-to-roll manufacturing of photovoltaic cells and modules that can be readily scaled up to high production volumes.    DETAILED DESCRIPTION - Forming active layer coating involves: forming molten mixture of at least one metal of group IIIA and metallic nanoparticles containing elements of group IB; and coating substrate (202) with film formed from molten mixture. An INDEPENDENT CLAIM is included for a photovoltaic cell comprising: base electrode (204); top electrode (210); and active layer (206) disposed between base electrode and top electrode, where active layer contains IB-IIIA-VIA alloy, and is formed from molten mixture containing at least one metal of group IIIA and metallic nanoparticles containing elements of group IB.    DESCRIPTION OF DRAWING(S) - The figure shows schematic diagram of the photovoltaic cell comprising active layer coating.    Substrate/base layer (202)    Optional adhesion layer (203)    Base electrode (204)    Group IB-IIIA-VIA layer/active layer (206)    Window layer (208)    Transparent conductive oxide layer (209)    Transparent electrode/top electrode (210)    Layer of metal fingers on transparent electrode (211)