Synthesis of Dye and Perovskite-Based Sensitizers and Electrolytes
Extraction of Pigments from Natural Dyes and Preparation of Dye-Sensitizer Solutions
Solutions of various fruit and vegetable pigments were obtained from fresh fruit and vegetables. All fresh fruits and vegetables were crushed and added to ethanol and acetone. The mixture was then centrifuged to get the required dye. Figures 5.4-5.8 shows some of the fruit and vegetables used in this study.
a. Pomegranate (Anthocyanin) Dye
To extract anthocyanin pigment from pomegranate, fresh fruits were peeled. After drying at room temperature, the peel was ground into a powder then 100 g was weighed and placed in a round-bottomed flask. Solvent (40:60 ethanokwater; 500 ml) was added. The flask was heated in a water bath at 60°C for 60 mins. The solution was then filtered to obtain the required dye.
FIGURE 5.4 Some fruits and vegetables used in the study: (a) pomegranate, (b) raspberry, (c) spinach, (d) orange peel, and (e) tomato
FIGURE 5.5 Images of extracted natural dye solution: (a) pomegranate, (b) raspberry, (c) spinach, (d) orange peel, and (e) tomato
FIGURE 5.6 The used part of fruits and vegetables: (a) red beans, (b) orange peel, (c) barley grass
FIGURE 5.7 Extracted natural dye solutions: (a) red beans, (b) orange peel, (c) barley grass b. Raspberry (Anthocyanin) Dye
Raspberry contains a red/purple anthocyanin pigment that can be attached to a Ti02 layer and works as a sensitizer. To extract the pigment, ripe raspberries were washed multiple times with water to remove impurities and contaminations. The cleaned fruits were ground to a paste using a pestle and mortar. Ethanol (20 ml) was added and the mixture refluxed for 90-200 minutes at 60°C. The resulting liquid was filtered using filter paper to extract the dye.
FIGURE 5.8 Structures of extracted natural dye pigments: (a) chlorophyll, (b) p-carotene, (c) anthocyanin
c. Spinach (Chlorophyll) Dye
Spinach leaves were first scrubbed with acetone then transformed into a paste by grinding. Acetone was added and the paste was ground again. The prepared solution was dispensed over filter paper in a funnel and acetone was poured over to extract the dye.
d. Orange Peel ф-carotene) Dye
Fresh oranges were purchased from a nearby market. After washing with de-ionized water, the oranges were precisely peeled. The peel was dried in a vacuum heater for around 10 h at 50°C then ground into powder in a mortar. Around 50 g of the powdered sample was put into a measuring cylinder and 150 ml supreme ethanol added. Subsequently, the blend was shaken for 5 h, shielded from daylight and kept at 50°C. This concentrate solution was utilized as a sensitizer in the synthesis of DSSC.
e. Tomato (Lycopene) Dye
Lycopene extract is produced from a tomato variety that has a high lycopene content, within the range of 150 to 250 mg/kg. This variety is not generally sold in market for edible use but produced specially for lycopene extract. The lycopene extract was prepared by crushing tomatoes into crude tomato juice. Ethanol (2 ml) was added to the tomato juice and filtered with filter paper.
f. Red Bean (Anthocyanin) Dye
To extract the anthocyanin pigment from red beans, we purchased fresh red bean seeds, crushed them and eliminated their white part. The resulting material was ground using a pestle and mortar to get anthocyanin dye.
g. Barley Grass (Chlorophyll) Dye
Barley grass leaves were scrubbed with acetone and transformed into a paste by grinding. Acetone was added and the paste ground again. A filter paper was attached
FIGURE 5.9 Stepwise synthesis of ethyalammonium tri-lead iodide: (a) ice bath process; (b) precipitate collection; (c) collected precipitate
FIGURE 5.10 The formation of CH,NH,PbI3. (a) Synthesized precipitate of methyl ammonium iodide; (b) recrystallized perovskite; (c) solution of methyl ammonium tri-lead iodide
to a funnel and the paste dispensed over the paper. Acetone (30 ml) was poured drop by drop on the paste. The barley grass chlorophyll was collected from the funnel, allowed to settle in a beaker, and collected in a clean petri dish [Figure 5.6 (a-c) and Figure 5.7].
Synthesis of Perovskite-Based Sensitizers
a. Synthesis of ethylammonium tri-lead iodide (CH,CH2NH,PbI3)
The perovskite sensitizer CH,CH2NH,PbI, was synthesized as follows. Ethylamine (10 ml) and HI (10 ml) were stirred in a conical flask at 0°C for 2 h then heated at 60 °C for 2 h. The precipitate was collected then washed twice with petroleum ether and dried at 100°C in vacuum oven for 24 h. The as- synthesized. dried CH,CH,NH,I powder (2.234 g) was mixed with Pbl, (6.016 g) at a 1:1 molar ratio in 10 ml DMF solvent. The solution was stirred at 60°C for 2 h. The resulting CH,CH,NH,PbI, solution was used as the sensitizer.
b. Synthesis of Crystals and Powder of Methyl Ammonium Tri-Lead Iodide (CH,NH,PbI_,)
Methyl ammonium iodide (CH,NH,I) was prepared by mixing methylamine (27.86 ml) in HI (30 ml) followed by ice-bath treatment at ~0°C for 2 h. The resultant product was put into the oven (60°C) overnight for complete evaporation. The precipitate of CH.NH.I was collected in a round-bottomed flask and washed thoroughly using diethyl ether. The final white precipitate was dried at
FIGURE 5.11 Solid polymer electrolyte preparation (a) PEO film poured in a petri dish, and (b) electrolyte solution containing PEO+KI+I,
100°C in a vacuum oven for 24 h (Figure 5.10a) then dissolved in ethanol and kept in a refrigerator for crystallization. The resultant CH,NH,I was put in the vacuum oven at 60°C for 24 hours prior to further processing.
CH,NH,PbI, solution was prepared by taking an equimolar ratio (1:1) of CH.NH.I and РЫ,. The as-synthesized CH,NH,I powder (0.395 g) was mixed with Pbl, (1.157 g) in gamma-butyrolactone (2 ml). The overall solution was continuously stirred for ~4 h at 60°C, resulting in a solution of CH,NH,PbI, (Figure 5.10c). This perovskite solution was used as a light sensitizer by spin coating it on a working electrode for making PSSC.
c. Synthesis of Crystals and Powder of CH,NH,SnCl,: A New Class of Lead- Free Perovskite Material for Low-Cost Solar Cell Applications Methyl ammonium chloride (CHXNH,C1) was prepared by mixing methyl- amine (30 ml) and HC1 (32.3 ml) in a round-bottomed flask. The product was put into a vacuum oven (60°C) overnight to dry. The CH,NH,C1 precipitate was washed thoroughly using diethyl ether and the resultant white precipitates dried at 100°C in a vacuum oven for 24 h. to get a powdered form of methyl ammonium chloride.
To produce CH,NH,C1 crystals, CH,NH,C1 powder was dissolved in ethanol and the solution heated at 60° C for 4 h then kept in the refrigerator for 3 days until recrystallization occurred. The product w'as filtered out and kept in a vacuum oven at 80°C for 48 h.
CH,NH,SnCl, powder and crystal solutions were synthesized by dissolving CH,NH,C1 powder and crystals, respectively, (0.395 g) with SnCl, (1.157 g) in DMF (2 ml), followed by stirring at 60°C.