Effect of Solvent Variations in the Alcothermal Synthesis of Template-Free Mesoporous Titania for Dye-Sensitized Solar Cells Applications

Abstract

A series of 14 mesoporous titania materials has been synthesized using the simple alcothermal template-free method and various alcohols, such as methanol, propanols and butanols, as solvents. All materials were characterized by both wide and small angle XRD, which exhibited the anatase phase with short-range ordered mesoporous structure that is still forming during post synthetic temperature treatment in most of the investigated materials. Nitrogen adsorption–desorption isotherms confirmed the mesoporous structure with surface area ranging from 241 to 383 m2g- 1 and pore volumes from 0.162 to 0.473 m3g-1, UV-Vis diffuse reflectance showed the redshift of the absorption edge and the bandgap decrease after post synthetic calcination of the materials presented. The TEM, FT-IR, DTA and TG measurements have been made to well characterize the materials synthesized. The mesoporous samples obtained were applied as anode materials for dye-sensitized solar cells and showed good activity in photon-to-current conversion process with efficiency values ranging from 0.54% to 4.6% and fill factors in the 52% to 67% range. The photovoltaic performances were not as high as those obtained for the materials synthesized by us earlier employing ethanol as a solvent. The differences in the electron lifetime, calculated from electrochemical impedance spectroscopy results and varying between 4.3 to 17.5 ms, were found as a main factor determining the efficiency of the investigated photovoltaic cells.

How Can the Introduction of Zr4+ Ions into TiO2 Nanomaterial Impact the DSSC Photoconversion Efficiency? A Comprehensive Theoretical and Experimental Consideration

“…Metalloxane bondings M–O–M’ (M and M’ = Zr, Ti) at about 475–625 cm −1 are formed via M–OR (M = Ti, Zr, and R = isopropoxide, n-propoxide) and water hydrolysis, followed by a condensation process of creating in situ M–OH and M–OR (or other M–OH) groups [ 60 , 61 , 62 ]. The narrow peak at 1385 cm −1 corresponds to the σ(C–H) bonding from alkoxy groups, and it is being overlapped with C–O stretching vibration caused by alkoxy residue [ 60 , 63 ]. The isopropanol and n-propanol residues’ bands at about 2854–2974 cm −1 may be attributed to the –CH 2 and –CH 3 symmetrical and asymmetrical stretching bonds [ 64 ].…”

“…The above observations may be concluded that prepared materials have mesoporous structures created by aggregates built of spherical TiO 2 nanoparticles [ 74 ]. Undoubtedly, the structure of used precursors (isopropoxide and n-propoxide alkoxy chains) can act as semi-templates and induce pores’ growth in investigated materials [ 63 ].…”

“…However, the J SC sharp decline in the case of 5.6% Zr 4+ may be caused by carbon residues, the presence of which has been confirmed by XPS and FTIR results described above. According to the literature data, carbon impurities significantly impact charge transport and recombination processes, leading to photocurrent density weakness [ 63 ].…”

“…As shown in Table 7 , the longer the electron lifetime, the higher photoelectric conversion efficiency with a slight difference between 1.2% and 3.7% content of Zr 4+ ions in examined nanomaterials. It can be explained as a strong impact of injected electron lifetime on recombination and photon-to-current conversion processes [ 63 ]. Electron injection and recombination processes are contradictory mechanisms.…”