Design, production and industrial applications of ferroelectric photovoltaic cells

In this thesis, LaFe1-xMnxO3 (x = 0, 0.5, and 1) ferroelectric powders were prepared via sol-gel method for dye-sensitized solar cell applications. With this context, precursor solutions were synthesized from all nitrate salts of the respective cations (La, Fe and Mn), using distilled water as a solvent, and citric acid monohydrate and ammonium hydroxide as chelating agents. The obtained gel films were dried at 200 °C for 2 hours and then annealed at temperatures of 500 and 850 °C for 2 hours in air. The thermal, structural, microstructural, particle size, optical and magnetic properties of the powder samples were characterized by Differential Thermal Analysis-Thermogravimetric Analysis (DTA-TGA), Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Particle Size Analyzer (PSA), UV Vis Spectrophotometer and Vibrating Sample Magnetometer (VSM) machines. DTA-TGA results revealed that endothermic and exothermic reactions are observed at temperatures between 29 °C and 1000 °C due to solvent removal, combustion, decomposition, oxidation, and phase formation of the samples. The spectrum of La-Fe-Mn based powders annealed at 500 °C and 850 °C shows an absence of absorption bands corresponding to organics and hydroxyl groups. FTIR spectra of, in the range 400-1000 cm-1, all perovskite samples confirm the presence of MO bonds (M=La, Fe, and Mn) in different sites. XRD findings show that the as-synthesized perovskite powders have excellent crystallinity, and Scherrer's Equation is used for the estimation of crystalline sizes (within 20 nm to 36 nm). Survey scan and high-resolution XPS spectra of La-3d5, Fe-2p and Mn-2p for LaFeO3, LaMnO3 and LaFe0.5Mn0.5O3 samples are given. SEM analysis revealed that xerogels have agglomerated into dense networks and their particle sizes are in the range of ∼4 μm to 40 μm because of their high water-holding capacity, after heat treatment, they show poorer water holding property and their particle sizes become lower such as at 500 oC in the range of ∼50 nm to 1500 nm and 850 oC in the range of ∼50 nm to 250 nm. The particle size distributions were denoted for all-ceramic powder materials, and values were determined in the range of 58-1400 nm, respectively. UV-Vis Spectroscopy analysis results show that the optical band gap values (Eg) as measured on all particles were found in the range of 0.93 - 2.42 eV. In addition to all analyses, the annealed powders show strong ferromagnetic behavior. All three materials synthesized at both temperatures show ferromagnetic properties and the ferromagnetic properties of both Fe-based ferroelectric powders decrease with increasing annealing temperature. These results revealed that there is a possibility to further increase the performance and efficiency of perovskite-based cells. These ferroelectric powders were used in dye-sensitized solar cell (DSSC) applications. In the DSSC, two FTO coated conductive glass cell contacts. One of these conductive glass surfaces was coated the first TiO2 and then with a doctor blade technique using a paste-like ferroelectric material powder (LaFeO3) using Triton X-100, while the other conductive glass surface was coated with Pt. These two surfaces are placed on top of each other with a 5 mm offset and clipped on both sides. Electrolyte (containing iodide/tri-iodide redox couple) is injected as the transfer medium between the two surfaces. With the solar simulator, the current-voltage values of the solar cell were obtained open-circuit voltage (Voc) is 0,3V, short circuit current (Isc) is 0.0000142A, Vmax is 0.2 V, Imax is 0.0078 mA, Fill Factor (FF) is 0.366197%, and their efficiency ((η-PCE) was calculated as 0.001114%. With this thesis, a successful ferroelectric photovoltaic cell has been obtained and it is aimed to be a guide for future studies.