The diblock copolymer PTPA-b-PS consisting of poly(4-butyltripheneylamine) (PTPA) and polystyrene was prepared by atom transfer radical polymerization followed by C-N coupling polymerization. Three types of block copolymers with different contents of polystyrene segment were prepared. The formation of block copolymer was confirmed by H-1 NMR spectra and gel permeation chromatography (GPC) profiles. Time of flight (TOF) measurement revealed that the block copolymer showed higher hole mobility up to 1.3 x 10(-4) cm(2)/Vs compared with PTPA homopolymer. The surface morphology of block copolymer films blended with [6,6]-phenyl-C-61- butyric acid methyl ester (PCBM) was investigated by Atomic force microscopy (AFM). Introduction of polystyrene segment provided microphase-separated structures with domain sizes of around 20 nm. The photovoltaic device based on PTPA-b-PS, PTPA, and PCBM exhibited higher efficiency than that of homopolymer blend system.