Spectrum Response Enhancement of Organic Solar Cell Using a Poly(3-hexylthiophene) Photosensitizing Layer

We report here the photovoltaic performance of a solar cell using poly-{[4,8-bis[(2-ethylhexyl)oxy]-benzo[1,2-b:4,5-b']dithiophene-2,6-diyl]-alt-[3-fluore-2-(octyloxy)carbonyl-thieno[3,4-b]thiophene-4,6-diyl]} (PBDT-TT-F):[6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM) as the photoactive layer in combination with a thin poly(3-hexylthiophene) (P3HT) film as a photosensitizing layer. PBDT-TT-F strongly absorbs light in the wavelength range of 550-700 nm, but it absorbs relatively weakly in the range of 350-550 nm. In contrast, a P3HT film shows intensive absorption ability in the 450-600 nm region, suggesting that the absorptions of these two materials complement each other to give a broad range. An organic solar cell with the structure indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene)-polystyrenesulfonic acid (PEDOT:PSS)/P3HT/PBDT-TT-F:[6,6]-phenyl C61-butyric acid methyl ester (PC61BM)/LiF/Al was fabricated in which P3HT was deposited between the hole transporting layer (PEDOT:PSS) and bulk heterojunction (BHJ) photoactive layer (PBDT-TT-F:PC61BM). This solar cell exhibited improved spectrum response in the wavelength range of 450-600 nm compared with one without a P3HT layer, which is attributed to the photosensitizing effect of the P3HT film. Optimization of the thickness of P3HT led to an increase of short-circuit current density (J(SC)) from 11.42 to 12.15 mA.cm(-2)