Stepwise co-sensitization as a useful tool for enhancement of power conversion efficiency of dye-sensitized solar cells: The case of an unsymmetrical porphyrin dyad and a metal-free organic dye |
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| Affiliation: | 1. R & D Center for Engineering and Science, JEC Group of Colleges, JEC Campus, Kukas, Jaipur 303101, Rajasthan, India;2. Laboratory of Bioinorganic Chemistry, Department of Chemistry, University of Crete, Voutes Campus, P.O. Box 2208, 71003 Heraklion, Crete, Greece;3. Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, India;1. Department of Chemical Engineering, Faculty of Petroleum, Gas, and Petrochemical Engineering, Persian Gulf University, Bushehr, 75169, Iran;2. Department of Petroleum Engineering, Faculty of Petroleum, Gas, and Petrochemical Engineering, Persian Gulf University, Bushehr, 75169, Iran;3. Department of Physics, Faculty of Science, Persian Gulf University, Bushehr, 75169, Iran;4. Algae R&D Centre, Environmental and Conservation Sciences, Murdoch University, Murdoch, 6150, Western Australia, Australia;1. Analytical and Spectroscopy Division, VSSC, India;2. Polymers and Special Chemicals Group, VSSC, India;1. RIAM School of Materials Science and Engineering, College of Engineering, Seoul National University, Kwanakro 1, Kwanakgu, Seoul, 08826, South Korea;2. Polymer Hybrid Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul, 02792, South Korea |
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| Abstract: | A tertiary arylamine compound (DC), which contains a terminal cyano-acetic group in one of its aryl groups, and an unsymmetrical porphyrin dyad of the type ZnPorph]-L-H2Porph] (ZnP-H2P), where ZnPorph] and H2Porph] are metallated and free-base porphyrin units, respectively, and L is a bridging triazine group functionalized with a glycine moiety, and were synthesized and used for the fabrication of co-sensitized dye-sensitized solar cells (DSSCs). The photophysical and electronic properties of the two compounds revealed spectral absorption features and frontier orbital energy levels that are appropriate for use in DSSCs. Following a stepwise co-sensitization procedure, by immersing the TiO2 electrode in separate solutions of the dyes in different sequence, two co-sensitized solar cells were obtained: devices C (ZnP-H2P/DC) and D (DC/ZnP-H2P).The two solar cells were found to exhibit power conversion efficiencies (PCEs) of 6.16% and 4.80%, respectively. The higher PCE value of device C, which is also higher than that of the individually sensitized devices based on the ZnP-H2P and DC dyes, is attributed to enhanced photovoltaic parameters, i.e. short circuit current (Jsc = 11.72 mA/cm2), open circuit voltage (Voc = 0.72 V), fill factor (FF = 0.73), as it is revealed by photovoltaic measurements (J–V curves) and by incident photon to current conversion efficiency (IPCE) spectra of the devices, and to a higher total dye loading. The overall performance of device C was further improved up to 7.68% (with Jsc = 13.45 mA/cm2, Voc = 0.76 V, and FF = 0.75), when a formic acid treated TiO2 ZnP-H2P co-sensitized photoanode was employed (device E). The increased PCE value of device E has been attributed to an enhanced Jsc value (=13.45 mA/cm2), which resulted from an increased dye loading, and an enhanced Voc value (=0.76 V), attributed to an upward shift and increased of electron density in the TiO2 CB. Furthermore, dark current and electrochemical impedance spectra (EIS) of device E revealed an enhanced electron transport rate in the formic acid treated TiO2 photoanode, suppressed electron recombination at the photoanode/dye/electrolyte interface, as well as shorter electron transport time (τd), and longer electron lifetime (τe). |
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| Keywords: | Co-sensitization Dye sensitized solar cells Power conversion efficiency |
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