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We have used Suzuki coupling to synthesize a series of maleimide-thiophene copolymers presenting pendent 2-hydroxyethyl and 6-hydroxyhexyl units. The maleimide-thiophene copolymers containing different contents of OH groups were then reacted with 3,3 0 -dimethoxy-4,4 0 -biphenylene diisocyanate (DMBPI) in solution to form the interchain-linked polymers. The interchainlinked polymers exhibited excellent solubility in organic solvents. The average molecular weight and thermal stability of the copolymers increased after interchain linking with DMBPI. The wavelengths of maximum absorption of the interchain-linked copolymers were red-shifted relative to those of the corresponding side-chain copolymers. The energy level of the lowest unoccupied molecular orbitals and highest occupied molecular orbitals decreased after the copolymers had undergone interchain linking with DMBPI. We fabricated polymer solar cells (PSCs) from blends of the interchain-linked copolymers and Keywords: fullerene derivative; maleimide-thiophene copolymer; polymer solar cell INTRODUCTIONThe development of novel low-band gap p-conjugated polymers is an attractive research area because bulk heterojunction polymer solar cells (PSCs) incorporating them can be fabricated at low cost with large areas, flexible shapes, light weight and solution processability. [1][2][3][4][5][6] The photoactive layer in most bulk heterojunction cells is based on a blend of an electron-donor conjugated polymer and an electronacceptor fullerene derivative, typically [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM). Several recent efforts have focused on the synthesis of a new low-band gap conjugated polymers that improve the absorption of solar radiation and increase charge mobilities. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] In addition to the intrinsic characteristics of the polymer, the amount of PCBM in the blend, 17,18 the compatibility of the polymer and PCBM, the morphology of the photoactive layer 19-21 and the deviceprocessing conditions all have important roles affecting the photovoltaic (PV) performance of PSCs. [8][9][10]22,23 Photo-energy conversion efficiencies (Z) of 47% have been achieved for PSCs based on blends of poly(thiophene) derivatives and fullerene derivatives. [7][8][9][10]24,25 In addition to the short-circuit current densities (J SC ) and values of Z that are typically measured, recent investigations have also been made into optimizing the PV efficiency stability of PSCs. For example, incorporation of a ultraviolet (UV) shielding layer into a PSC can