February 11th has been designated as the international day of women and girls in science to promote their participation in STEM (Science, Technology, Engineering, Mathematics) activities [1]. For the first time in 2020, the Physics Institute of BUAP (IFUAP) opens its doors to young girls to talk about science and technology. Here, at the BUAP IF2 building, you can find me at the Lab-205 which is designed for the development of hin films and nanoparticles of novel materials.
This laboratory is where I am doing my postdoctoral project but take it easy. I am not going to explain physic or chemistry stuff. I just one to share with you the experience these young girls had. These girls come from the social science area (economics, politics, etc.), which makes the activity a little bit difficult because we speak different languages. The challenge here is to explain: How does a thin-film solar cell work?
Challenge accepted!
LED is possible due Semiconductors
In Fig.1, I was explaining about LED technology (Light Emitting Diode). To catch their attention, I placed 40 LEDs of different colors on the worktable, and I asked them. “Take your favorite color LED and watch it through the light” and tell me, What can you see inside?. If you have the opportunity to observe it, you will find two metallic pieces with different sizes (Watch this image).
- The small one is the positive (+) terminal and is called the anode. The most important thing here is that this terminal is connected to a p-type semiconductor.
- The bigger metallic component is the negative (-) terminal called the cathode. This terminal is connected to an n-type semiconductor.
With this small piece of information. You have almost identified the core of the LED technology using observation: 1) Its made of semiconductors and 2) Inside, there is a sandwich called the pn-junction. Right now we can unassemble LED technology in 4 essential parts:
- + positive terminal (Anode)
- p-type semiconductor
- n-type semiconductor
- – negative terminal (Cathode)
See Fig. 2 and compare the LED with another kind of semiconductor can you identify our prototype Solar cell?
Solar cell and LED share the same configuration
The solar cell and LED share the same configuration because both of them are diodes. A LED produces light from electric energy; on the other hand, a solar cell transforms light into electricity. But wait a minute I want to tell you about the activity we did to find why these devices are similar.
Activity: Measure the generate Voltage of a LED
Material:
- LED
- Multimeter (in voltage mode)
- Lamp or light source (you can use your cellphone).
Objective: To measure the voltage of the LED in two light conditions 1) Ambient using the room illumination and 2) Use the lamp of your cell phone and illuminate the LED the closest possible.
Instructions: Connect the multimeter to the LED. In this configuration, you are going to measure the generated voltage in different light conditions. 1) Ambient and 2)direct light (You can use your cellphone or sunshine).
Conclusion: The voltage value will increase when the light is near the LED. This phenomenon happens when light shines the pn-junction and the internal electric field increase due to the generation of an excess of free carriers (electrons and holes). In ambient light condition, the voltage will be V = 0.03 Volts, but when the power of the light increases the voltage rise near V = 1.1 Volts. This behavior is physics (Solid State Physics), and all of this happens due to Semiconductors, they are transforming light into electricity.
In Fig.3, you can watch the young girls paying attention to science communication of our group. We were talking about semiconductors, solar cells, and thin films. The thin-films we are developing in this lab are compound semiconductors like Sb2S3 – Antimony sulfide, CuS – Copper Sulfide, Bismuth Sulfide-Bi2S3. When these films are placed in the correct sandwich configuration np-junction (diode), we can fabricate a solar cell.
I think this activity helps the girls to discover that science is a way of think and live. Science pushes forward technology and brings wellness to our life.
In the second activity, we describe and compare the homemade thin-film solar cells. This prototype was made using antimony sulfide, a novel material available as a mineral in Mexico. Do you want to read more?
References
- [1] (2020, February 11) Woman and girls in science day, United Nations, Retrieved from https://www.un.org/en/observances/women-and-girls-in-science-day
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