تعزيز اداء الخلية الشمسية MWCNTs-ZnO / TiO2 نانوية التركيب

Performance Enhancement of MWCNTs-ZnO/TiO2 Nanostructure Solar Cell

Innovations in materials technology in the fields of photovoltaic (PV) play a key role in the paradigm shift from fossil fuels to renewable sources. The solar energy sources are one of the renewable energies that exhibited several advantages such as low cost, simple assembly, and environmentally friend. The main objectives of this study are to fabricate dye-sensitized solar cell (DSSC) and improve their performance.
Platinum thin films were prepared on the FTO substrate with different H2PtCl6 precursor concentration 2.5, 5, 10, and 15 mM using spin-coating methods as a counter electrode. On the other hand, titanium butoxide (Ti(OBu)4) precursor was used to prepare titanium dioxide nanorods TiO2 as a photoanode using hydrothermal method directly on the FTO glass with different hydrochloric acid (HCl) – water (H2O) ratios of 12.5-7.5, 10-10, 7.5-12.5 and 5-15 ml and etching times of 24, 48 and 72 h. In addition, ZnO NRs were synthesized on TiO2 NR using seeding and growth process. 0.01 M seed solution of zinc acetate was used to prepare zinc oxide (ZnO) seed layer on TiO2 NR by spin coating device. Then hydrothermal method was used to grow ZnO NR in aqueous solution of 0.03M zinc nitrate hydrate, hexamethylenetetramine (HMT) and deionized water (DI). Moreover, multi-walled carbon nanotubes (MWCNT) were insetted into ZnO seed layer with different concentration of 0, 0.5, 1 and 1.5 wt.%. Finally, photoanode was immersed in N719 dye for 24 h and assembled with the counter electrode (CE) to complete a sandwich-structure DSSC then sealed and filled by Meltonix 45 µm and electrolyte (Iodolyte HI-30) respectively.
X-ray diffraction (XRD) results illustrate that the TiO2 samples have polycrystalline rutile phase structures with preferred orientations (101) and (002). ZnO NRs were grown on the (002) plane. Furthermore, there is no distinct MWCNT peak due to the small amount of MWCNT perhaps cannot be detected. As well as the variation of the MWCNT concentration led to shaft the ZnO peak position. The increase of HCl concentration leads to an increase in the rod diameter of the TiO2 NRs and decrease the length as exhibited in scanning electron microscopy (SEM) Image. While the etching time leads to a decrease in the diameter and length of TiO2 NRs.
The morphology of ZnO has a rods shape and the crest of ZnO NRs has a hexagonal shape. In addition, the Energy-dispersive X-ray spectroscopy (EDX) spectrum verified that the prepared samples were pure and no other impurities were found. Moreover, the ultraviolet-visible (UV-Vis) spectroscopy shows the optical properties of synthesized TiO2 NRs where declare that the optical band gap decreased with increasing the HCl concentration while it increased with increasing the etching time. The ZnO growth on TiO2 NRs leads to an increase in the Eg of the optical electrode whereas reduces with an increase in MWCNT content.
Current density-voltage (J-V) measurement show that the increase in the H2PtCl6 precursor concentration leads to an increase of the solar cell efficiency of 1.666, 2.067, 2.96 and, 2.96 for single layer film while gradually decreased to 2.956, 2.938, 2.891 and 2.816 with increase in the H2PtCl6 precursor concentration for double layers. On the other hand, the optimum efficiency (η) of DSSC based on TiO2 NRs was 3.255% at sample ET where the preparation condition (7.5 ml HCl + 12.5 H2O) with 48 h etching time. The DSSC constructed with ZnO/TiO2 based photo-anode shows remarkably improved efficiency (η) of 20 % where improved the electron transfer.
The solar cell efficiency of insetted MWCNT into ZnO seed layer of the fabricated cells are 3.938, 4.358, 4.047 and 3.203 with increase the MWCNT concentration. At the best conditions, the incorporation of MWCNTs at 0.5 wt% increases the conversion efficiency by approximately 10%. Finally, the total improving on the TiO2 nanostructure photo anode was 34%.