Bulk heterojunction materials composed of poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene):: Ultrafast electron transfer and carrier recombination

The results of time-resolved spectroscopic studies of the structurally ordered liquid-crystalline polymer, poly(2,5bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene), PBTTT, and of composites of PBTTT with the soluble fullerene derivative, [6,6]-phenyl-C-61 butyric acid methyl ester, PCBM are reported. These ultrafast studies focus on the photogeneration of mobile carriers in PBTTT/PCBM composites following sub-picosecond electron transfer from PBTTT to PCBM. The recombination and loss of mobile carriers at early times (approximately 200 ps following photoexcitation) were measured with different ratios of the PBTTT and PCBM components (1: 1 and 1:3) by monitoring the time decay of the photoinduced absorption features associated with the charge-transferred state. The results are well-correlated with the solar-cell efficiency obtained using PBTTT/PCBM bulk heterojunction materials.