Functional nanoferrite thin films are used in various fields of our life. There are many different methods used to fabricate thin films including sputter deposition, flash laser evaporation pulsed laser deposition (PLD), chemical vapor deposition (PVD) and spin-coating process. In each of these methods, it produces an amorphous phase of the deposited film. To produce a crystalline film, an additional high-temperature processing is required. The high-temperature process can lead to considerable constraints in combining the desirable characteristics of a crystalline nanoferrite thin film with those of thermally unstable substrates and other device components. High-temperature thin-film processing is also a considerable cost to manufacturing. This chapter will report a simple procedure of the sol-gel precursor method for fabrication of NiZn nanoferrite (Ni 0.3 Zn 0.7 Fe 2 O 4) thin films and spin-coating method in coating a chemical solution. This method generally provides for both low-temperature deposition and crystallization of NiZn nanoferrite thin films.
In this study, a CQDs at different concentration is used to modify the TiO2 photoelectrode band gap which can improve light absorption of DSSC. The photoelectrode is immersed in different CQDs concentration at 2.5, 5.0, 7.5 and 10 mg/ml to study the effect on TiO2. It was found that photoelectrode with 7.5 mg/ml CQDs was successfully narrowing the TiO2 band gap and generated the highest photocurrent and power conversion efficiency at 17.06 mA/cm2 and 7.23% respectively, compared to pristine TiO2 (PT) at 10.94 mA/cm2 and 4.63% . The band gap narrowing mechanism for CQDs- TiO2 is obtained from the Tauc’s plot method using absorption spectra. The result shows a pristine TiO2 photoelectrode (PT) band gap is 3.38 eV, upon existing of CQDs, the band gap of all photoelectrodes with CQDs at 2.5, 5.0, 7.5 and 10 were reduced to 3.30 eV, 3.28 eV, 3.09 eV, and 3.29 eV respectively. PG 7.5 cell with lowest band gap at 3.09 eV generates effective electron transport from N719 dye to CQDs/ TiO2 layer compared to other photoelectrodes. The band gap narrowing effect is attributed from chemical bonds of Ti-O-C molecules between CQDs/TiO2. Thus, extra energy states are introduced between CQDs and TiO2. The location of these energy will present a quantum confinement effect which narrow the CQDs-TiO2 band gap which extend the light absorption to visible region.
Graphene quantum dots (GQDs) is used to enhance light absorption in the visible region of DSSC by sensitising method. The used of GQDs in photoelectode may effect the N-719 dye loading on photoelectrode and the study is done by ultraviolet spectroscopy (Uv-Vis). Initially, the TiO2 photoelectrode films is sensitised in ∼5 nm GQDs to overcome TiO2 photoelectrode drawback such as random electron transport and short-circuit current. Then, photoelectrode films is sensitised in N-719 dye to excite the electrons in TiO2 film. PG 7.5 adsorbed only 0.103 x 10-7 mol cm-2 N719 dye while PT at 0.527 x 10-7 mol cm-2. The pristine TiO2 photoelectrode (PT) adsorbed more than 80.4% of N-719 dye compared to PG 7.5 photoelectrode and other TiO2-GQDs photoeletrodes (PG 2.5, PG 5.0 and PG 10). As a result, the used of GQDs for TiO2 photoelectrode is reduced the intake of expensive N-719 dye for DSSCs. This happened because some of the functional groups in the GQDs solution such as hydroxyl and carboxyl groups are biocompatible with TiO2 which allows more adsorption sites of GQDs onto TiO2 surface. Thus, after GQDs molecules were occupied on the TiO2 surface, not many sites were available for N719 dye molecule. Therefore, it might reduce the N719-dye intake in the DSSC device, which can reduce the fabrication cost of DSSC and give good impact on environment.
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