*Question E6F10:
What is the most common material used in power-generating photovoltaic cells?*  

*Correct Answer is  B: Silicon*  

### AI Response: (may contain errors)  

The most common material used in power-generating photovoltaic cells is silicon. Here's a breakdown of why this is the correct answer and why the other options are not typically used for this purpose.

### Correct Answer: Silicon
- **Why it's correct**: 
  - Silicon is the most widely used semiconductor material in photovoltaic (PV) cells due to its abundance, efficiency, and well-understood properties. It has a suitable bandgap of about 1.1 eV, which allows it to effectively convert sunlight into electricity. Silicon-based solar cells can achieve efficiencies of around 15-22% in commercial applications.

### Incorrect Choices:
- **A: Selenium**
  - While selenium can be used in some types of solar cells (like thin-film cells), it is not as efficient or widely used as silicon. Selenium-based cells typically have lower efficiency and are less common in commercial applications.

- **C: Cadmium sulfide**
  - Cadmium sulfide (CdS) is primarily used as a thin-film material in conjunction with other materials (like cadmium telluride) for solar cells. However, it is not the most common material for photovoltaic cells overall, and its use is limited due to toxicity concerns associated with cadmium.

- **D: Indium arsenide**
  - Indium arsenide (InAs) is used in high-efficiency solar cells, particularly in space applications, but it is expensive and not suitable for mass production. Its use is limited compared to silicon, which is more cost-effective and widely available.

### Summary
- **Silicon** is the dominant material for photovoltaic cells due to its efficiency, cost-effectiveness, and availability.
- Other materials like selenium, cadmium sulfide, and indium arsenide have specific applications but are not as commonly used in the general market for solar energy generation.

This understanding of materials used in photovoltaic cells is crucial for the Extra Class exam and for grasping the fundamentals of solar technology.