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In this regard, Lab101 from CIDS-ICUAP, led by Dr. Roman Romano, contributed to the workshop on Solar Cells & Thin Films, where children learned how solar cells work and performed their first scientific experiment by producing a thin film. Since our audience consisted solely of children, we designed hands-on activities where they could safely interact with materials. From past outreach events, we recognized the importance of letting participants touch and play with the devices, as it significantly enhances their learning experience. Parents often worry about their child damaging a device or ruining an experiment. However, we believe that touching while learning new concepts is a critical part of learning..

Every activity lasted 10-15 minutes, allowing groups of 4-7 children to explore other activities. In our workshop, the first activity explained how solar cells (silicon) transform solar energy into electricity. The second activity demonstrate how solar cells at BUAP are fabricated on special glass substrates called TCOs (Transparent Conductive Oxide) wich conduct electricity. Finally, the third activity revelaed that the conductive properties of TCOs comes from a very thin layer placed on the top of the glass. This layer is a Thin Film (SnO₂:F) of nearly 500 nm, which is difficult to see with our bare eyes, so we fabricate a thin film made of nail polish in front of them.

The following sections describe the methodology and experience of each activity:

1^st activity: Harnessing the Power of the Sun: Understanding Solar Cells

In this activity, we demonstrated how solar energy is converted into electricity using a solar cell. They learn that this is possible with a device called a Solar Cell. Figure 1 shows Dr. Jesus Capistran talking to four children about energy conversion. To open the conversation, he began by sitting on the ground and asking if they had any experience with solar cells. To our surprise, one child mentioned seeing solar cells in toys. Dr. Capistran then made them to think of other places where solar cells are used (Have you ever noticed solar cells around your neighborhood?), such as in public lamps, gas stations rooftops, and solar-powered toys like cars.

After the discussion, the children play with a solar cell (silicon mini-module) connected to a small electric motor with a plastic propeller (see video 1). As soon as sunlight reached the solar cell, the motor started spinning the propeller. In this demonstration, children realize that the motor only turns on when exposed directly to the sun. Because if they cover a part or the solar cell, the energy is insufficient to power the motor.

This demonstration made it easy for the children to understand how a solar cells transform light into electrical energy, which can power small devices.

In Video 1, you can see how a silicon solar cell (silicon mini-module) powers the motor under direct sunlight. This demonstration allowed the children to see with their own eyes how energy is transformed. The cherry on top of this activity was when Dr. Capistrán explained the entire process: First, sunlight is converted to electricity by the solar cell. Then, this electricity flows through the wires to power the motor. Maybe the children do not understand what energy is, but they now have hands-on experience manipulating a solar cell to power a propeller without using batteries.

We concluded this activity by asking them to imagine how large a solar cell would need to be to power the lights in their home. They didn’t know, but we help them visualize that a typical solar module (2.0 x 1.1 meters, silicon module ) would be about the size of a whiteboard in their classrooms.

To replicate this activity, you will need a silicon mini-module (6 volts, 100 mA, Area = 87×57 mm) connected to a micro-motor (3-5V, 0.15 A) with a plastic propeller. Ensure that the motor’s power does not exceed the 600 mW outpud provided by the solar cell (module) under full sunlight.

2^nd activity: Unveiling the Magic of Conductive Glass

In this activity, we introduced the children to a solar cell fabricated in our lab. This solar cell consist of three essential components: 1) a front electrode (special glass substrate), 2) an n-p semiconductor junction, and 3) a back electrode (carbon). We focused on the concept of electrical continuity and explained that there are three types of materials: a) conductors, b) insulators, and c) semiconductors.

Rather than using a multimeter to test electrical continuity (which involves sharop probes), we fabricated our own tester to let the children safely explore electricity. Figure 2 shows the device, whicn includes a buzzer connected to a pair of AA batteries. The buzzer sounds when the crocodile clips are touching each other, closing the electric circuit.

Each child used the tester to touch the surface of three materials:

1. The buzzer sounded when touching stainless steel (2.5×7.5 mm), demonstrating that metal conducts electricity.
2. The buzzer remained silent when touching a glass slide (2.5×7.5 mm), showing that electricity does not flow through glass.
3. Finally, the children tested TCO glass and found that it conducts electricity, identifying it as a special type of glass.

We concluded this activity by explaining that the TCO’s ability to conduct electricity comes from a thin layer of material (500 nm of SnO₂:F) on one side of the glass. By probing both sides, they discovered that only the coated side conducted electricity.

Video 2 shows the tester in action, closing the circuit and making the buzzer sound. This simple device helps explain electrical continuity in a fun and interactive way. We encourage you to fabricate your own tester to let your public play with electricity. The older kids were particularly interestet in electronic components and usually asked what each component was. Here, You can explain what is a battery, LED, electrical resistance, buzzer, and how cables conduct electricity.

3^rd activity: Hands-On Experiment to Create Your First Thin-Film

The final experiment introduced the concept of thin films. Figure 3 shows M.C. Gabriela Esquina and Dr. Erick Ramirez leading the children in producing a thin film using nail polish with the following methodology:

1. Fill a container with water.
2. Add one or two drops of transparent nail polish to form a film on the water’s surface.
3. Submerge a piece of cardboard into the water to catch the nail polish film.
4. Let the cardboard dry and observe the thin film.
5. Observe the reflection colors; wich resemble the rainbow colors.

This activity is incredible because the children can observed how the light interects with the thin film to produce the rainbow color (colors changes with respect to the film thickness). To make it more engaging, we asked them where else they might see this color effect. If they couldn’t remember, we reminded them to pay attention to soap bubbles the next time they or their parents do the dishes.

To finish the activity, we let each kit take home their cardboard as a gift for their parents. Now, trough this experiment, children learned what a thin film is and discovered that such films are used at BUAP to develop thin film solar cells.

Conclusion

During the 2024 Scientific Summer for Kids at the Botanic Garden at CU-BUAP, we hosted approximately 100 children. This event was made thanks to the effort of the ICUAP administration, particularly Dra. Carolina Moran, Dra. Susana Soto, and Dra. Beatriz Espinosa, as well as ther participation of researchers, postdocs and students from the Science Institute (ICUAP). We strongly believe that such outreach activities should continue every year to keep children in touch with science and technology and encouraging them to see these fields as a potential future career path.

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