NOVELTY - Forming (I) single-crystal thin-film material layer of first material comprises: depositing thin-film material layer on surface; laser-heating to crystallization temperature seed spot of thin-film material layer; extending seed spot into single-crystal seed line (111) by laser-heating crystallization zone adjacent to seed spot and drawing crystallization zone across thin-film material layer; and extending single crystal seed line across thin-film material layer by laser-heating crystallization zone adjacent to seed line and thawing crystallization zone across thin-film semiconductor layer.    USE - The method is useful for: forming single-crystal thin-film material layer of first material for use in photovoltaic device; and fabricating photovoltaic device or tandem photovoltaic device (all claimed).    DETAILED DESCRIPTION - Forming (I) a single-crystal thin-film material layer of a first material comprises: depositing a thin-film material layer on a surface comprising a substrate and a template layer on the substrate, where the thin-film semiconductor layer has an initial micro-structure comprising amorphous, nanocrystalline, microcrystalline or polycrystalline; laser-heating to a crystallization temperature a seed spot of the thin-film material layer, where the seed spot having size on the order of a critical size of nucleation of the thin-film material layer, and thus crystallizing the seed spot; extending the seed spot into a single-crystal seed line (111) by laser-heating at least one crystallization zone adjacent to the seed spot and drawing the crystallization zone across the thin-film material layer; and extending the single crystal seed line across the thin-film material layer by laser-heating a crystallization zone adjacent to the seed line and thawing the crystallization zone across the thin-film semiconductor layer. INDEPENDENT CLAIMS are also included for:    (1) fabricating (II) a photovoltaic device comprising depositing an electrical contact layer on the surface, depositing first thin-film semiconductor layer, where the first thin-film semiconductor layer has an initial micro-structure comprising amorphous, nanocrystalline or microcrystalline, laser-heating to a crystallization temperature a seed spot of the first thin-film semiconductor layer, where the seed spot having size on the order of a critical size of nucleation of the first thin-film semiconductor layer, and thus crystallizing the first seed spot into a single-crystal seed, extending the seed spot into a first single-crystal seed line by laser-heating the crystallization zone adjacent to the seed spot and drawing the crystallization zone across the first thin-film semiconductor layer, extending the first single crystal seed line across the thin-film semiconductor layer by laser-heating crystallization zone adjacent to the first seed line and drawing the crystallization zone across the first thin-film semiconductor layer, constructing a first junction using the first thin-film semiconductor layer, and applying contact metallization;    (2) fabricating a tandem photovoltaic device comprising depositing electrical contact layer on a transparent substrate, depositing thin-film semiconductor layer, where the thin-film semiconductor layer comprises at least first junction sublayer and second junction sublayer, each junction sublayer further comprising a P-type, an intrinsic, and an N-type sub-sublayer, laser-heating to crystallization temperature a seed spot of the thin-film semiconductor layer, extending the single-crystal seed spot into single-crystal seed line by laser-heating the crystallization zone adjacent to the seed spot and drawing the crystallization zone across the thin-film semiconductor layer, where the crystallization zone crystallizing the sublayer of the second junction sublayer and without crystallizing at least the intrinsic sublayer of the first junction sublayer, and applying a contact layer;    (3) forming a tandem photovoltaic device comprising depositing first electrical contact layer on transparent substrate, patterning electrical contact layer comprising first metallic contact layer and a second metallic contact layer, depositing first thin-film semiconductor layer, laser-heating to crystallization temperature a seed spot of the first thin-film semiconductor layer, extending the seed spot into single-crystal seed line by laser-heating the crystallization zone adjacent to the seed spot and drawing the crystallization zone across the first thin-film semiconductor layer, depositing second thin-film semiconductor layer, where the second thin-film semiconductor layer chemically different from the first semiconductor layer, forming first junction at the first thin-film semiconductor layer, forming second junction at the second thin-film semiconductor layer, and applying the second electrical contact layer; and    (4) a photovoltaic device comprising first junction and second junction, where the first and second stacked, the first and second junction formed in a chemically same semiconductor material, the first semiconductor junction having crystalline structure and the second semiconductor junction having amorphous structure.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of the seed line prior to extension of single-crystal growth across the remaining semiconductor layer.    Single-crystal seed line (111)    Untreated material (112)