Department of Chemistry, Institute of Science, Banaras Hindu University Varanasi 221005, India
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| 2. Experimental procedures
TiO2 paste was prepared by blending 200 mg as obtained TiO2 powder, 1 drop of Triton X100 and 3 drops of acetic acid in an agate mortar. The mixture was grounded thoroughly for 10 min and then 2 ml of ethanol was slowly added whilst grinding continued for another 10 min. The paste was then applied to a clean fluorine doped tin oxide (FTO, 2 mm thick glass with 15 ÿ/sq surface resistivity, SnO2:F coating, Solaronix SA, Switzerland) coated transparent conducting glass. TiO2 pastes were on the FTO conductive glass by a doctor-blade method in order to obtain a TiO2 film with a thickness of 10 ÿm and an area of 0.25 cm2 . The TiO2 film was kept at room temperature for one day to dry and then sintered at 450 °C for half an hour in air and al lowed to cool down to room temperature. A platinum counter electrode was prepared by the deposition of Pt catalyst (T/SP paste, Solaronix SA) on a conductive glass plate followed by annealing at 400 °C for half an hour in air. The amount of dye loading on the TiO2 surface was obtained using the dye desorption technique (Pang et al., 2012; Hwang et al., 2012). 2.2. Synthesis of TNP and G-TNP nanoparticles by sol-gel route 2.4. Anchoring of photoanode with N719 dye and DSSC assembly The N719 dye-coated photoelectrode was dipped into 5.0 ml 0.1 M NaOH solution and in a mixed solvent of ethanol & deionized water (1:1 v/v ratio). technique as it does not require any high end equipments, hazardous chemicals or high temperatures (Rao et al., 2015a, b; Patidar and Jain, 2017; Yedurkar et al., 2016). In the present work we have synthesized TiO2 by a facile sol-gel method using Bixa orellana seeds extract as a capping agent to reduce the size and increase pore diameter of TiO2 nanoparticles. XRD, FTIR, HR-SEM, HRTEM measurements were used for structural character izations and their phase and pore diameters were analyzed using BET measurements. The photovoltaic studies were performed with the cells employing photoanodes made with conventional TiO2 nanoparticles (TNP) and the plant seed grown TiO2 nanoparticles (G-TNP) and their cell performances are discussed. Fresh seeds of Bixa orellana (B. orellana) were collected from Botanical garden, Banaras Hindu University, Varanasi. The seeds were vacuum dried at 60 °C. The dried B. orellana seeds were crushed using mortar and pestle into fine powder; 2 g fine powder of B. orellana seeds was immersed in 100 ml ethanol and kept in dark for 24 h. Ethanol was used for the extraction of dye as the main constituents present in the Bixa orellana seed cis-bixin is insoluble in water. The extract was fil tered and the filtrate was used for the synthesis of TiO2 nanoparticles. The images of B. orellana extract, absorption spectrum of the solution of B. orellana and the structure of its constituents (Gómez-Ortíz et al., 2010; Dias et al., 2011; Scotter et al., 1994) are given in Fig. 1(d). 2.3. Fabrication of TNP and G-TNP film electrode (photoanode) and counter electrode 2.5. Dye adsorption Moreover, though the natural pigments used for DSSC production are mostly of plant origin, natural pigment of bacterial origin have also been recently used as well in DSSC (Silva et al., 2019). Therefore, green synthesis of nanoparticles by using biofriendly materials has received considerable attention in recent years. 2.1. Extraction of natural dye G-TNP nanoparticles were prepared using precursor materials of Titanium (IV) butoxide [Ti(OBu)4], acetic acid (ACS reagent, ÿ99.7%), isopropanol (anhydrous, 99.5%) which was purchased from Sigma Aldrich, natural dye extract and deionized water (DI H2O). Initially, 10 ml of titanium butoxide was added in 80 ml of isopropanol and the mixed solution was then refluxed for 4 h at 70 °C to get clear solution. Therefore, the properties of Bixa orellana are mainly due to stabilize the bixin component in its bixin state (Calogero et al., 2018; Gómez-Ortíz et al., 2010). In the synthesis of TiO2 using this extract, some of the bioactive components can act as stabilizing agent, while the others can act as capping agent. Therefore, it is anticipated that the synergistic effect of stabilization and capping efficiency of Bixa orellana seed ex tract might influence the morphology and size of synthesized TiO2 nanoparticles. The DSSC devices were fabricated with TNP and G-TNP TiO2 films coated with N719 dye as a working electrode and a Pt-coated counter electrode in a sandwich type structure. The platinum catalyst-coated counter electrode was placed on top so that the conductive side of the counter electrode faced the dye-coated TiO2 film and the cell was sealed on three sides by using the spacer; one side was left open for the injection of electrolyte solution. An iodide-based solution was used as the liquid electrolyte, consisting of 0.2 M lithium iodide and 0.02 M iodine in acetonitrile, was injected into the assembled cells through open side and was drawn into the space between the electrodes by capillary ac tion. The lids (copper wires) were attached on the electrode using silver paste, which was finally covered with Araldite and dried. Bixa orellana contains several bioactive components, such as poly saccharides, vitamins, proteins, lipids, polyphenols, heterocyclic and carbonyl compounds (Selvi et al., 2013; Taham et al., 2015). A fresh bixa orellana seed extract mainly contains cis-bixin, however lesser quantities of trans-bixin and cis/trans-norbixin are also present. How ever, cis-bixin which is soluble in polar organic solvents to which it imparts an orange color may be readily converted to the all-trans isomer due to its instability in the isolated form in solution. The trans Bixin is the more stable isomer and has similar properties to the cis isomer with only difference that it exhibits a red color in solution. BET surface area, pore size and pore volume of the samples were evaluated by using a Gemini VII 2390t instrument from Micromeratics instrument corporation, operating at 77 K. TEM images of the synthe sized TiO2 nanoparticles were taken using a FEI Technai transmission The solution was cooled at room temperature followed by the addition of 5 ml glacial acetic acid to obtain solution A. Solution A refluxed for 2 h at 70 °C and then cooled at room temperature followed by the ad dition of 5 ml of natural dye extract . This was followed by refluxing for 2 h at 70 °C and then cooling at room temperature. After that, solution A was added drop wise into solution B (15 ml of deionized water) under vigorous stirring. The mixed solution was stirred continuously for 2 h and aged for 24 h at room temp. For comparison, TiO2 was prepared following same procedure, without use of natural dye extract (TNP) also (Fig. 2). The precipitates were recovered by centrifugation (10,000 rpm, RT) and were washed thoroughly with ethanol and deionized water followed by drying in air oven at 60 °C for 24 h. Finally, the powder was calcined at 450 °C for 1 h. For solar cell testing, the TNP and G-TNP films were coated with standard ruthenium based red dye (N719), bis(tetrabutylammonium)- cis- di(thiocyanato)-N,Nÿ-bis(4-carboxylato- 4ÿ- carboxylic acid-2,2ÿ-bi pyridine)ruthenium(II) (Solaronix SA, Switzerland). N719 dye was at tached to the TNP and G-TNP surface by immersing the TNP and G-TNP electrodes in a 10ÿ5 M solution of the dye in ethanol for 12 h. The non adsorbed dye was washed off by using anhydrous ethanol. Various capping agents are used to synthesize TiO2 nanoparticles to avoid agglomeration effect and to reduce average particle size for overall enhancement of the performance of DSSC. Bio-capping agents provide eco-friendly, facile and one step synthesis of the nanoparticles with sustainable and easy scale up to the industrial production at lower cost (Khade et al., 2015; Kumar et al., 2014; Al-Attafi et al ., 2017). IC Maurya, et al. Solar Energy 194 (2019) 952–958 953 Machine Translated by Google |