Raman shifts and optical absorption spectra of bulk heterojunction films were measured to elucidate the origin of the optimum annealing parameters. A series of device optimization studies revealed 413K to be the optimum annealing temperature, leading to a power conversion efficiency of 2.95%. The highest power conversion efficiency coincides with the highest peak in the UV-visible absorption and the lowest full width at half maximum of the CC symmetric stretching signal in the Raman spectra. The changes observed in the vibronic shifts could be useful in obtaining information about the optimal performance and processing conditions for polymer optoelectronic devices.
We report the fabrication of a chlorophyll-layer-inserted poly(3-hexyl-thiophene) (P3HT) solar cell. A significant enhancement in the light-to-current conversion efficiency of up to 1.48% with a fill factor of 0.32 was achieved in a solar cell with a device structure of indium tin oxide anode/poly (3,4-ethylene dioxy-thiophene):poly(styrene sulfonate)/P3HT/chlorophyll/Al cathode under the standard air mass 1.5 irradiation (20mW∕cm2). These results suggest that the generation of an internal electric field is mainly due to a difference between the highest occupied molecular orbital of the P3HT (donor) and the lowest unoccupied molecular orbital of the chlorophyll (acceptor), which permits the transfer of photoinduced electrons from P3HT to chlorophyll.
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