A novel series of soluble conjugated random and alternating copolymers (PFO-TST) derived from 9,9-dioctylfluorene (FO) and 1,1-dimethyl-3,4-diphenyl-2,5-bis(2'-thienyl)silole (TST) were synthesized by palladium(0)-catalyzed Suzuki coupling reactions. The feed ratios of FO to TST were 99:1, 95:5, 90: 10, 80:20, and 50:50. Chemical structures and optoelectronic properties of the copolymers were characterized by elemental analysis, NMR, UV absorption, cyclic voltammetry, photoluminescence (PL), electroluminescence (EL), a photovoltaic cell, and a field effect transistor. The elemental analyses of the copolymers indicated that FO and TST contents in the copolymers were very close to the feed compositions. The random copolymers exhibited a PFO-segment-dominated UV absorption peak at similar to 385 nm and a narrow band gap TST absorption at similar to 490 nm. For the alternating copolymer, only a broad absorption band was found, demonstrating a mixed and TST-dominated electronic configuration. Compared with the solution PL, complete PL excitation energy transfer from the PFO segment to the TST unit could be achieved by film PL at lower TST content. It was found that the EL spectra of the copolymers with a device configuration of indium-tin oxide/poly(3,4-ethylenedioxythiophene)/poly(vinylcarbazole) (PVK)/ copolymer/Ba/Al were red shifted and had better red light CIE coordinates with improved external quantum efficiency, compared with corresponding device performances without the PVK layer. With the alternating copolymer as the electron donor and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester as the electron acceptor, an energy conversion efficiency of 2.01% was achieved under an AM1.5 simulated solar light at 100 mW/cm(2), which is among the highest values so far reported for bulk-heterojunction photovoltaic cells. The field effect hole mobility of the alternating copolymer is 4.5 x 10(-5) cm(2)/(V s) using polyacrylonitrile as an organic insulator on a gate electrode.