NOVELTY - Forming a patterned organic thin film comprises: (a) providing a substrate; (b) forming a thin film of a block copolymer comprising a positive-tone polymer block and a negative-tone polymer block, where the thin film has periodic microdomains; (c) aligning the periodic microdomains of the thin film; (d) exposing at least a portion of the thin film from (b) to deep-UV or e-beam radiation to differentially affect the positive-tone polymer blocks and negative-tone polymer blocks in the exposed portion of the thin film; and (e) exposing the thin film from (d) to a solvent.    USE - The method is useful for forming a patterned organic thin film (claimed), which is useful for dye-sensitized solar cells.    ADVANTAGE - The method is capable of economically forming the patterned organic thin film with large area reproducibility using the block copolymers, which are highly sensitive to deep-UV, e-beam and soft x-ray irradiation.    DETAILED DESCRIPTION - Forming a patterned organic thin film comprises: (a) providing a substrate; (b) forming a thin film of a block copolymer comprising a positive-tone polymer block and a negative-tone polymer block, where the thin film has periodic microdomains; (c) aligning the periodic microdomains of the thin film; (d) exposing at least a portion of the thin film from (b) to deep-UV or e-beam radiation to differentially affect the positive-tone polymer blocks and negative-tone polymer blocks in the exposed portion of the thin film such that an exposed pattern, and, optionally, an unexposed portion, of thin film is/are formed; and (e) exposing the thin film from (d) to a solvent such that the unexposed portion of block copolymer thin film and selected regions of the exposed portion of the thin film are removed, and a patterned organic thin film of the negative-tone polymer blocks or a patterned organic thin film of the positive-tone polymer blocks is formed. INDEPENDENT CLAIMS are included for:    (1) a block copolymer having structure of formula (-(A)x-(B)y1-) (I); and    (2) a thin film comprising the block copolymer.    A = polystyrene block, polyhydroxystyrene block or its substituted analog (preferably poly(4-hydroxystyrene), poly(p-chlorostyrene), poly(p-bromostyrene), poly(p-iodostyrene) or poly(pchloromethylstyrene)), where the A block is a styrene block or a hydroxystyrene block, the fluorinated block comprises fluorinated alkyl methacrylate repeat units or a mixture of fluorinated alkyl methacrylate and alkyl methacrylate, and the fluorinated alkyl methacrylate block has 5-1000 fluorinated alkyl methacrylate repeat units and 0-950 alkyl methacrylate repeat units;    B = fluorinated block comprising at least one fluorinated monomer (preferably poly(fluromethacrylate), poly(fluoromethacrylate-co-methacrylate), poly(2,2,2-trifluoroethylmethacrylate) or poly(2,2,2-trifluoroethyl methacrylate-co-methyl methacrylate)), where the A block and/or B block has one or more crosslinkable moieties; and    x, y1 = 5-1000.