Visual Observation and Practical Application of Dye Sensitized Solar

Laboratory Experiment Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

pubs.acs.org/jchemeduc

Visual Observation and Practical Application of Dye Sensitized Solar Cells in High School Energy Education Sen-I Chien,† Chaochin Su,*,† Chin-Cheng Chou,‡ and Wen-Ren Li§ †

Institute of Organic and Polymeric Materials/Research and Development Center for Smart Textile Technology, National Taipei University of Technology, Taipei 10608, Taiwan ‡ Department of Science Education, National Taipei University of Education, Taipei 10671, Taiwan § Department of Chemistry, National Central University, Taoyuan 32001, Taiwan S Supporting Information *

ABSTRACT: The present study describes the design of a simple teaching module for each student to fabricate a dye-sensitized solar cell (DSSC) that could power a small fan motor. The significance of this laboratory exercise is to stimulate students’ motivation by visualizing the light being converted into electricity, which is then switched over to kinetic energy, and to inspire them to understand the mechanistic working principles of solar cells and gain the concepts of sustainable green energy. The developed DSSC teaching module could easily power a small fan motor under the light of a halogen lamp, a conventional light bulb, or a compact fluorescent lamp. In addition, the fabrication process allowed replacing the expensive massive pressing machine by using electric irons that are readily available in daily life and made this module cost-effective and easy to assemble by school students. The field studies reveal that both junior and senior high school students were able to complete the module in 2.5 h class session and more than 80% of students successfully constructed the DSSCs to harvest the light to propel their fan motors. KEYWORDS: High School/Introductory Chemistry, Laboratory Instruction, Hands-On Learning/Manipulatives, Dyes/Pigments, Photochemistry

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INTRODUCTION

and gearboxes in model cars and are not suitable to teach the concepts and mechanisms. On the other hand, third generation solar cells, such as dyesensitized solar cells (DSSCs) with manageable fabrication setups, can be assembled entirely by school students. Compared to the previous generation solar cells, DSSCs are inexpensive, flexible, and eco-friendly.2 Several recent research reviewers have revealed the numerous applications of DSSCs in energy education of schools. For example, natural dyes from plants were employed in the DSSC modules for the freshmen chemistry laboratories with the aim to familiarize students with basic concepts of solar cells.3 The literature also reports that natural dyes extracted from vegetables are used in the laboratory to attract students’ interests.3−6 Smith et al. developed a simple laboratory exercise for the construction of DSSCs using household ingredients such as toothpaste.7 The

Increasing energy consumption, population growth, fossil fuel depletion, and global warming are directing us from the dependence of fossil fuels to alternative renewable energy resources. In high school laboratories, green energy education comprising teaching modules of solar cells is highly important to develop awareness and interest about sustainable energy research among school students. Essentially, the teaching kits should be simple, low-cost, safe, and easy to handle by school students. Among all green energy resources, solar energy is the most abundant and can be easily recognized and visualized by students. Solar cells are electric devices that can directly convert sunlight into electricity. Generally the solar cells can be divided into three generations.1 Crystalline silicon and thin film solar cells are the first two generations; however, their technical approaches are too complicated and inappropriate for the junior and senior high school students to able to produce. Moreover, most of the above solar-cell teaching aids are finished products, which only allow students to install motors © XXXX American Chemical Society and Division of Chemical Education, Inc.

Received: July 3, 2017 Revised: May 2, 2018

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DOI: 10.1021/acs.jchemed.7b00484 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

Laboratory Experiment

education modules (see the student handout in the Supporting Information).

common outputs of the above and other devices were exhibited by an expensive solar simulator, a potentiostat, or a multimeter,8,9 which might be less attractive for high school students. Itzek-Greulich et al. explored grade 9 students learning an experiment topic on starch chemistry. The results showed that for the experimental group, hands-on activities helped improve learning motivation, situational interest, and situational ability as well as reduced boredom.10 Swarat et al. discovered that both hands-on science and technology activities elevate students’ interest. The study also discovered that students pay attention to the content of the activities rather than the topics and learning objectives.11 Shaner et al. designed a hands-on experiment for high school and university curricula, where the students were required to perform solar energy conversion and catalyzation. Results obtained from subsequent survey questionnaires indicated that this experiment elevated the students’ learning results, interest in learning chemistry, and motivation in performing research in the future.12 To the best of our knowledge, high school students would be fascinated or motivated by a teaching module that demonstrates the conversion of solar energy to electricity by either powering a small light-emitting diode (LED) or propelling a fan motor. This kind of experience might spark the student’s imagination and motivate them to pursue further study in the field of energy technology. In the pilot study, tests were conducted using multimeters and light bulbs, which the students seemed not so attractive. By changing the test equipment to small motor fans, the students’ interest was increased substantially. However, none of previously reported DSSC teaching modules has delivered such exciting visual results. The main objective of the present study is to stimulate students’ enthusiasm by visualizing the conversion of sunlight, electricity, and kinetic energy and to encourage them to explore sustainable technologies. To enhance the working power, some researchers have used large-scale, series, or parallel DSSC modules.13−19 To apply these reported research results to teaching kits, the above arrangement would result in the increase of material cost or the complication of manufacturing process in the classroom. Therefore, this study is intended to design an affordable solar cell fabrication process and offer opportunities for the students to learn the mechanism of power generation through a hands-on activity. The designed teaching kit can also be utilized in the teaching demonstration accompanied by teacher-guided explanations to teach students the functions of anode, cathode, and electrolyte (Figure 1).2,20−23

Materials

The fluorine-doped tin oxide (FTO) 32 × 30 mm2 conductive glass substrate (Solaronix 8Ω), commercial-grade photo catalytic nano-TiO2 slurry (TDP-TP-T transparent TiO2 paste, Jintex Corporation Ltd.), and conductive silver threads (PTG-5582B, Yibisi) were purchased from MKE Tech (Make Energy Technology, Taiwan). The platinum sputtered six-holed stainless steel plates (32 × 30 mm2, 50 μm) were obtained from Eternal Materials (Eternal Materials Co. Ltd., ETERDSC EL1415). The 0.3 mM dye solution was prepared by dissolving Z907 dye (cis-bis(isothiocyanato)(2,2′-bipyridyl-4,4′dicarboxylato)(4,4′-dinonyl-2′-bipyridyl)ruthunium(II)) (Figure 2, from MKE) in acetonitrile and tert-butyl alcohol (a

Figure 2. Molecular structure of Z907 dye cis-Bis(isothiocyanato)(2,2′-bipyridyl-4,4′-dicarboxylato)(4,4′-dinonyl-2′-bipyridyl)ruthunium(II).

volume ratio of 1:1).24,25 The triiodide/iodide redox couples (I3− or I2/I−) containing 1,2-dimethyl-3-propyl imidazolium iodide (DMPII), lithium iodide (LiI), iodine (I2), 4-tertbutylpyridine (TBP) in acetonitrile (Ac)26−28 were employed as the electrolytes in DSSCs. A film of polymer thermoplastic Surlyn 1702/1706 (DuPont: 30, 60 μm) was utilized to afford space for the electrolyte between the anode and cathode. The heat-pressed machine (SC-A009) was purchased from SC-Tech (Shuo Chang Technology Company, Taiwan), and the electric irons were made by Panasonic. (NI-E510T). Device Fabrication

As shown in Figure 3, assembling of the DSSC module was illustrated in the following steps: (1) obtain the anode for dipping the dye; (2) submerge the photo anode in dye solution; (3) heat press the dyed anode and Surlyn film

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EXPERIMENTAL OVERVIEW In this section, we describe the materials, device fabrication, and module performance as well as the field study of DSSC

Figure 1. Working mechanism of dye-sensitized solar cells (DSSCs).

Figure 3. Device fabrication process. B




together; (4) assemble cathode; (5) inject the electrolyte into the DSSC module; and (6) use hot glue to seal the injection holes and ensure no bubble present in the electrolyte. The anode of DSSC (Figure 4) was submerged into the dye solution for 5 h. The edges of the anode were gently clean by wiping with acetonitrile-soaked cotton swabs (Figure 5).

Figure 7. Surlyn heat pressed onto the anode.

Figure 4. Scheme of DSSC anode.

Figure 8. Heat pressed by electric iron.

After cooling, the bottom layer of PET film was removed and assembled with cathode (Figure 9). The resulted device was

Figure 5. Schematic preparation of dye adsorbed TiO2 photoanode.

The thermoplastic Surlyn is covered by top and bottom layers of PET films and its size is shows in the schematic diagram (Figure 6). After the top layer of PET film was removed, the anode was inserted into the Surlyn and sealed using heat-pressed machine at 130 °C for 35 s (Figure 7).

Figure 9. Cathode of DSSC.

then sealed using either a heat-pressed machine at 150 °C for 35 s or an electric iron around 170−190 °C for 50 s. The extra Surlyn covering silver threads was carefully removed using a knife. Subsequently, the electrolyte solution was injected into the holes of the DSSC module slowly via syringe. After ensuring that no air bubbles are in the electrolyte, the hot glue was used to seal the holes and the solar device was ready for testing (Figure 10). To demonstrate the conversion of light energy to electricity, then to kinetic energy, the assembled device was connected to a small fan motor (Figure 11). Senior high school students were allowed to use a soldering iron to connect wires between anode

Figure 6. Thermoplastic Surlyn film.

The cost of a heat press machine is approximately US $3200, which might be over the budget for some high schools, particularly those that are lack of resources. To overcome this difficulty, we used an electric iron (US $31) as an alternative to press the cell for 50 s (Figure 8). The heat setting of the electric iron was maintained at the temperature suitable for flax/linen (around 170−190 °C). C




presentation. Two sessions for 13 nonscience teachers were also organized during the education training service period. Each session was 2 h in duration with a brief slideshow introduction in the beginning. The success rate of each session was recorded and collected and the comprehensive investigation was then carried out to evaluate the feasibility of this teaching module for either senior high school or junior high school from the field study results.

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Figure 10. Schematic description of complete assembling of the DSSC teaching module.

HAZARDS Many hazardous chemicals are used in this module; consequently, it is recommended that both students and instructors wear activated carbon masks that can adsorp organic substances through the experiment and wear latex gloves when handling chemicals or organic substances to prevent skin contact. For example, when they are using any heating machines, electric irons, welding torches, and the glue guns, they should wear resistant nitrile gloves to prevent being burned, stabbed, or cut, and the work should be carried out under the surveillance of a trained teaching assistant to avoid burn injuries. Syringes with needles were used to extract bubbles in the electrolytes as well as excess electrolytes. Do not apply force to move a plunger. Too much pressure can irretrievably bend the plunger. Use extreme caution in handling needles to avoid bending, contamination, or accidental personal injury. Most important of all, the students could only operate the syringes inside the fume hood, wore gloves and surgical masks, and were accompanied by teaching assistants.

Figure 11. Test DSSC under light.

Hazard Chemicals Statements for Teacher

and cathode. Alligator clips were recommended to replace the wires for junior high school students.

(1) Acetonitrile: Highly flammable liquid and vapor. It would be harmful if swallowed, in contact with skin, or inhaled. Wear protectine gloves/protective clothing. (2) tert-Butyl alcohol: Highly flammable liquid and vapor. It causes serious eye irritation, respiratory irritation, and drowsiness. (3) Iodine: Harmful in contact with skin or if inhaled. Causes eye, skin irritation. Causes damage to organs through prolonged exposure if swallowed. (4) Z907: Cause skin and eye irritation. May cause respiratory irritation and allergic skin reaction. The regulations on the use of hazards chemicals within the school district, state, and nation in which the school is located should be carefully checked, especially by junior and senior high-school teachers.

Module Performance

To investigate the performances of assembled DSSC modules, different light sources [halogen lamp (20 W), tungsten lamp (100 W), and compact fluorescent lamp (27 W)] were explored. The minimal distance (cm) to operate the motor fan for halogen, tungsten, and compact fluorescent lamp (CFL) is 10.0, 5.0, and 3.0 with the luminosity (LM) 30 500, 6560, and 2150, respectively. The voltage and amperage were measured using a Digital Multimeter (Model DT-830B). Each experiment was carried out twice, and the testing results from eight individual modules were averaged. To ensure that these DSSC modules are capable of producing consistent results, durability tests were conducted under the halogen lamps (20 W) for 14 days continuously and the voltage and current were recorded every day.

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Field Studies of DSSC Education Modules

STUDENT LEARNING OBJECTIVES The key learning objectives are as follows: Device assembly: To fabricate a solar cell by assembling the anode and cathode. Electrolyte Injection: To inject the electrolyte and seal injection holes with hot glue after ensuring that no bubbles are present in the device. Performance Testing: To measure the voltage and amperage of the light-generated current using a multimeter and testing the solar cell can power a small fan. Evaluation: To determine whether the students understand the working principle of photovoltaic cells, the current amplification effect of parallel connection, and the applications of solar cells.

The field studies of the DSSC education modules involved three different groups: senior high school students, junior high school students, and nonscience teachers. Four sessions were conducted in senior high school during their club hours or energy education classes. Each 2 h session was given to 40 students supervised by 2−8 teaching assistants to prevent injuries to the untrained students. At the beginning, a PowerPoint slideshow was presented to emphasize the urgency of developing renewable energy, the mechanism of the DSSC, and how to generate electricity from solar cells. After performing the experiments, all field study results were collected in the end. Another ten sessions for junior high school students were organized in the summer camps for interested students. About 50 students were involved in each 2.5 h filed study course with simplified PowerPoint D



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RESULTS AND DISCUSSION In the following sections, we present four categories: (1) reducing equipment cost by electric irons, (2) effects of different light sources, (3) durability test for the DSSC modules, and (4) field studies of teaching education kit. Reducing Equipment Cost with Electric Irons

To develop a practical low-cost teaching module, we aimed to replace the expensive heat-pressed machine with an electric iron. The photovoltaic parameters of the corresponding DSSCs are listed and compared in Table 1. The average efficiency η Table 1. Average DSSC Performances of Cells Prepared by Heat Press Machine and Electric Irons Figure 12. Durability test for the DSSC module for 14 days.

method

Voc (V)a

Isc (mA)b

Jsc (mA/cm2)c

FF

heat press machine electric irons

0.73 0.70

−37.47 −24.10

−5.95 −3.83

−0.64 −0.66

d

η (%)

e

module can be done in a few minutes to restore the cell to the operational condition, which demonstrated that the designed DSSC module is highly effective and flexible as a teaching aid.

2.77 1.73

a

Voc: open-circuit voltage. bIsc: short-circuit current. cJsc: short-circuit current density. dFF: fill factor. eη: solar energy conversion efficiency.

Field Studies of DSSC Education Kit

As shown in Figure 13, field studies were conducted in three different groups: senior high school students, junior high school

(1.73%) of modules using electric irons was 37% lower than that (2.77%) of a heat-pressed machine. This could be due to the difficulty in maintaining stable pressure by human hand and individual differences. Nevertheless, the energy generated by the modules using electric irons is sufficient to power small fan motors without any difficulty. The success of promoting renewable energy education partially lies in attracting students’ interests and experimental cost. By simply replacing the heatpressed machine with an electric iron, the cost can be significantly reduced up to 100 times. The fabrication process using the common household appliance became cost-friendly for high schools and might be able to inspire students that research is associated with daily life.

Figure 13. Average success rate of performing DSSC education modules by three groups, senior high school students, junior high school students, and nonscience teachers.

Effects of Different Light Sources

The effect of different light sources on the performance of DSSCs utilizing a heat press machine was investigated and displayed in Table 2. The minimal voltage and amperage

students, and nonscience teachers. The average success rate of performing DSSC education modules by senior high school students, junior high school students, and nonscience teachers was 88%, 84%, and 77%, respectively. The field studies of DSSC education kit indicated that the operation of these solar cell modules is independent of the participants. The easy and facile fabrication process of the designed teaching modules played an important role in boosting the overall success rate.

Table 2. Photovoltaic Parameters of DSSCs Illuminated under Halogen, Tungsten, and Compact Fluorescent Lamp (CFL) parameter

halogen lamp (20 W)

tungsten lamp (100 W)

CFL (27 W)

voltage (V) amperage (mA)

0.72 100.09

0.67 19.34

0.68 19.20

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SUMMARY A simple, easy to fabricate, low-cost, and safe teaching module of DSSC was developed for high school students. The goal of this exercise is to establish an exciting hand-on education kit for school students to visually experience the solar cell technology via propelling the plastic fan. In addition, the functions of the anode, cathode, and electrolyte and the photovoltaic mechanism of DSSCs were taught and illustrated. Home appliances such as light bulbs and electric irons were employed in this laboratory exercise to introduce the cost-down concept, attract students’ attention, and shorten the gap between academic research and real life. About 88% of senior and 84% of junior high school students can assemble their solar cells and run the corresponding motor fans successfully, which revealed the effectiveness of this module in teaching school students. By promoting this module in classroom, awareness for the

required to power the motor fan was 0.5 V and 10 mA, respectively. As shown in Table 2, these modules successfully propelled their fans under various light sources (halogen lamp, tungsten, and CFL). The performances of these modules are superior than that of handmade DSSCs used in previous study, which could only generate microampere scale of currents which are not sufficient to power a motor fan. Durability Test for DSSC Module

The results of the durability test show that the modules maintained similar and sufficient efficiencies for 14 days under halogen lamps (Figure 12). Over time, some of the electrolyte solution may evaporate due to sealing failure, which means there is no longer enough redox electrolytes to regenerate the sensitizers. However, reinjecting the electrolyte solution in the E




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concepts of green energy and energy sustainability can be stimulated and developed among students.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.7b00484. Details of student handout, questionnaire, and notes for setting up DSSC module (PDF, DOCX)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Sen-I Chien: 0000-0001-5976-9031 Wen-Ren Li: 0000-0001-9230-4957 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Funding for this research was provided by the Ministry of science and technology in Taiwan (MOST104-2113-M-027007-MY3). We express our thankfulness for the students and TAs who participated in this study.

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REFERENCES

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Visual Observation and Practical Application of Dye Sensitized Solar

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