TECHNOLOGY FOCUS - POLYMERS - Preferred Copolymer: In phase-separable block copolymer, the first heterocycle is thiophene, optionally substituted in one or both of the 3-position and the 4-position, the substitutions being independent of each other, and where the second heterocycle is selenophene, optionally substituted in one or both of the 3-position and the 4-position, the substitutions being independent of each other. The optional substituents are selected from nitro, carboxyl, formyl, and alkylcarbonyl, and alkyl optionally substituted with one or more of nitro, carboxyl, formyl, alkylcarbonyl and heteroalkylcarbonyl, or heteroalkyl optionally substituted with one or more of nitro, carboxyl, formyl, and alkylcarbonyl. The first monomer is selected from unsubstituted thiophene, thiophene that is substituted in the 3-position, thiophene that is substituted in the 4-position, and thiophene that is substituted in both the 3-position and the 4-position. The second monomer is selected from unsubstituted selenophene, selenophene that is substituted in the 3-position, selenophene that is substituted in the 4-position, and selenophene that is substituted in both the 3-position and the 4-position. First monomer of the first fully conjugated homopolymer is selected from unsubstituted thiophene, thiophene that is substituted in the 3-position, thiophene that is substituted in the 4-position, and thiophene that is substituted in both the 3-position and the 4-position; and the second monomer of the second fully conjugated homopolymer is selected from unsubstituted selenophene, selenophene that is substituted in the 3-position, selenophene that is substituted in the 4-position, and selenophene that is substituted in both the 3-position and the 4-position. The first fully conjugated homopolymer comprises formula (1-S); and the second fully conjugated homopolymer comprises formula (1-Se).R=independently selected from H, NO2, NH2, COOH, CHO, F, Cl, Br, I, BH2, OH, SH, SeH, OR1, SR2, SeR3, COR4, a functional group, and a hydrocarbon chain that is 1 to 100 carbon atoms in length that may or may not have hydrocarbon and heteroatomic substituents;R1-R4=each independently hydrocarbons that contain 1 to 100 carbon atoms; andm or n=2-10000.The first fully conjugated homopolymer is poly(3-hexylthiophene); and the second fully conjugated homopolymer is poly(3-hexylselenophene). The first fully conjugated homopolymer is poly(3-hexylthiophene); and the second fully conjugated homopolymer is poly(3-hexylselenophene). The molar ratio of 3-hexylthiophene to 3-hexylselenophene is greater than 1:2000 and less than 2000:1; the molar ratio of 3-hexylthiophene to 3-hexylselenophene is greater than 1:1000 and less than 1000:1, or is greater than 1:500 and less than 500:1, or is greater than 1:200 and less than 200:1, or is greater than 1:100 and less than 100:1, or is greater than 1:50 and less than 50:1, or is greater than 1:10 and less than 10:1, or is greater than 1:5 and less than 5:1, or is between 1:2 and 2:1; or the molar ratio of 3-hexylthiophene to 3-hexylselenophene is about 1:1. Preferred Composite: In the copolymer-nanocrystal composite, the phase-separable block copolymer is phase-separated. The copolymer-nanocrystal composite is crystalline. Phase-separable block copolymer is arranged in nanofibers. The set of nanocrystals is substantially associated with a phase of the phase- separable block copolymer; the set of nanocrystals is substantially arranged; the set of nanocrystals is arranged in a substantially periodic linear fashion; the set of nanocrystals comprises substantially spherical nanocrystals; the set of nanocrystals comprises cadmium-selenium nanocrystals; or the set of nanocrystals comprises an allotrope of carbon. It comprises compounds selected from cadmium selenide (CdSe), cadmium telluride (CdTe), cadmium sulfide (CdS), lead sulfide (PbS), lead selenide (PbSe), copper indium sulfide (CuInS2), copper indium selenide (CuInSe2), cadmium arsenide (Cd3As2), cadmium phosphide (Cd3P2), C60, phenyl-C61-butyric acid methyl ester, C70, phenyl-C17-butyric acid methyl ester, C84, carbon nanotubes and graphene. The mass ratio of the phase-separable block copolymer to the set of nanocrystals is about 1:1. The phase-separable block copolymer is in good electrical communication with the set of nanocrystals. Set of nanocrystals comprises nanocrystals with a conduction band below a lowest unoccupied molecular orbital (LUMO) level of the phase-separable block copolymer and a valence band below a highest unoccupied molecular orbital (HOMO) level of the phase-separable block copolymer. Preferred Device: The optoelectronic device is selected from a diode, a light-emitting diode, a transistor, a solar cell (preferred), a photodiode, and a light-emitting transistor. The device has efficiency between 0.1 and 15%; or the device has efficiency greater than about 2.7%. The film comprises fibers of the block copolymer having an average thickness of from 5 to 500 nm. The electron acceptor material comprises a fullerene, a fullerene derivative, a nanoparticle, nanocrystal, quantum dot, or its combination. It comprises a quantum dot selected from CdSe, CdTe, CdS, PbS, PbSe, CuInS2, CuInSe2, Cd3As2, Cd3P2, or its combination. The solar cell has a power conversion efficiency of at least 2.7% when exposed to simulated sunlight of an intensity of 1 Sun under AM1.5 G conditions. The film has an average thickness of between 5 and 50 nm; or the film has an average thickness of between 10 and 20 nm. It has nanomorphology that is thermally stable between 25 degrees C and 350 degrees C. The nanomorphology is stable at about 80 degrees C. Preferred Method: In adjusting set of properties of phase-separable block copolymer, the first fully conjugated homopolymer is poly(3-hexylthiophene) and the second fully conjugated homopolymer is poly(3-hexylselenophene). The molar ratio of 3-hexylthiophene to 3-hexylselenophene is greater than 1:200 and less than 200:1; or the molar ratio of 3-hexylthiophene to 3-hexylselenophene is about 1:1. The set of properties comprises morphological properties, or optical properties. In manufacturing solar cell, providing a semiconductor includes coating a substrate with the semiconductor composite material. In making photovoltaic device, the temperature of at least one of the solution and substrate is controlled to be in the range from 60 degrees C to 100 degrees C. The temperature of the solution is controlled to be in the range from 60 degrees C to 100 degrees C during step (ii); the temperature of the solution is controlled to be in the range from 70 degrees C to 90 degrees C during step (ii); the temperature of the substrate is controlled to be at least 40 degrees C during step (ii); or the temperature of the solution is controlled and/or the temperature of the substrate is controlled to form a film on the substrate, the film comprising fibers of the block copolymer having an average thickness of from 5 to 500 nm. The temperature of the solution is further controlled and/or the temperature of the substrate is further controlled to form a film having Ra of less than 3 nm. Applying the solution comprises forming the film on the substrate by spin-coating, drop casting, doctor blading, ink jet printing, evaporation, or its combination. The method further comprises drying the film formed in step (ii) at a temperature equal to or greater than the temperature of step (i). The film is maintained at a temperature greater than or equal to the temperature of step (i) throughout step (ii) and the step of drying the film. The method further comprises installing an electrode in contact with the film; and thermally annealing the film subsequent to installing the electrode. The substrate comprises a conductor layer. The solution is applied directly to the conductor layer. It further comprises an electron acceptor. The electron acceptor is selected from a fullerene, a fullerene derivative, a nanoparticle, nanocrystal, quantum dot, or its combination. Preferred Material: The acceptor material comprises a set of nanocrystals. The semiconductor composite material is crystalline. The set of nanocrystals is substantially associated with a phase of the semiconductor composite material; or the set of nanocrystals is arranged in a substantially regular or irregular array. The array is a substantially periodic linear arrangement. The film is formed directly to a substrate. The thickness of the film on the substrate is between 1 nm and 10000 nm, or between 5 nm and 8000 nm, or between 5 nm and 5000 nm, or between 5 nm and 2000 nm, or between 5 nm and 1000 nm, or between 10 nm and 800 nm or between 10 nm and 500 nm, or between 10 nm and 300 nm, or between 20 nm and 300 nm, or between 40 and 200 nm, or between 20 and 300 nm. The substrate comprises a conductive material or transparent layer. Conductive material is a semiconductor layer, a metal, indium tin oxide and/or the transparent layer is a plastic. The film is formed on the substrate by spin-coating, drop casting, doctor blading, ink jet printing, evaporation, or any other method or combination of methods used to deposit matter. The composite material is into a semiconductor layer for photovoltaic device. Preferred Cell: The cell has efficiency between 0.1 and 15%; or the cell has efficiency greater than about 2.7%. EXAMPLE - No suitable example given.