Improving optical absorption bandwidth using bi-layer bulkheterojunction organic photoactive medium

The optical absorption bandwidth of the thin films organic semiconductors composed of poly(3 hexylthiophene) (P3HT) and poly[[4,8-bis[(2-ethyhexyl)oxy] benzo(1,2-b:4,5-b')dithiophene-2,6-diyl][3-fluoro-2-[(2 ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), respectively, were studied. Photon harvest in the thin film organic solar cell was found to be improved employing P3HT:PCBM and PTB7:PCBM double layer. The optical absorption measurements clearly showed enhanced absorption bandwidth in bi-layer compared to the conventional type ternary molecules blend bulk-heterojunction structure using the same molecules. The device performances derived from the electrical measurements showed that the single layer devices appear to have higher power conversion efficiencies than the double layer which is attributed to the effectiveness of the charge transport processes in the two media. The life time measurement of the devices in ambient condition was investigated and discussed.