Syntheses and properties of conjugated polymer with thiophene-bridged BTI and indenoindene units for organic solar cells

We report the new conjugated polymers using dihydroindeno[2,1-a]indene moiety (ININE), electron-pushing unit with high planarity, for the organic solar cells (OSCs). Pull-push mode of conjugated polymers, P1 and P2, containing electron pulling unit of N-alkyl-2,2???-bithiophene-3,3???-dicarboximide (BTI) and electron-pushing unit of ININE were synthesized for the broader absorption of the solar radiation. By incorporation of electron pulling and pushing units using Stille polymerization with catalyst of Pd(0), the polymers were synthesized. Absorption peaks of the thin films of P2, with thiophene unit linking the electron-pulling and pushing units, was shifted to the region of longer wavelength than P1. Two synthesized polymers provided deep energy levels of highest occupied molecular orbital between -5.76 and -5.59 eV and suitable energy levels of lowest unoccupied molecular orbital between -3.65 and -3.55 eV.clos