Journal article

A Double-Band Tandem Organic Dye-sensitized Solar Cell with an Efficiency of 11.5 %

The absorption spectra of most org. dyes reported thus far used for mesoporous nanostructured dye-sensitized solar cells mainly cover the visible-light region. This has motivated research towards the development of new types of org. dyes(7-10) with absorption spectra extended to the near-IR and IR region. By adjusting the donor, linker, and acceptor units, this group developed a tandem Dye-sensitized Solar Cell in which the front subcell employs a ZrO2-doped nanostructured TiO2 semiconductor to improve the photovoltage and an org. 3-[2-(N,N-diphenylamino)-ethenyl]-phenoxazinyl-cyanoacrylic acid dye (TH305) to harvest sunlight in the 400-750 nm region, giving an efficiency of 9.05 % with a high photovoltage (794 mV), while the back subcell employs a normal TiO2 electrode sensitized with a different org. dye (HY103) to capture sunlight in the 500-800 nm region, achieving an addnl. efficiency of 2.45 %. The two sub-cells are sepd. by a double-sided fluoride-doped tin oxide conducting glass. Shifting the CB band of TiO2towards more neg. values is an effective way to improve the open-circuit photovoltage (Voc) and increase the DSC's efficiency. The two methods used to make the CB more neg. are : (a) adding an org. base, 4-tert-butylpyridine, to the electrolyte, and (b) doping the TiO2 with semiconductor materials with a more-neg. CB energy level (EcB), ZrO2, which has a wider band gap (ca. 5.0 eV) and a more-neg. CB level (-1.0 V vs. normal hydrogen electrode). The org. dye TH305 was chosen for the front subcell because its more neg. LUMO level (-1.28V vs. NHE) matches the ECB of ZrO2-doped TiO2. Undoped titania was used for the second sub-cell. The total conversion efficiency was 9.05%, with a Voc of 0.794V, and a Jsc of 15/20 mA/cm2.


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