---
title: "Working of a solar cell"
subject: "Energy Environment and Society"
chapter: 3
key: "semester_7/energy_environment_and_society:solar-cell-working"
source: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/solar-cell-working
site: BCT Engineering
---

# Working of a solar cell

Energy Environment and Society · Chapter 3: Renewable Energy Sources

- Asked in: 2070 Asar, 3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/energy_environment_and_society/solar-cell-working
- Whole chapter: https://www.bctengineer.com/md/semester_7/energy_environment_and_society/chapter-3

## Question

Write in short about the working of a solar cell.

## Short answer

A solar cell is a p-n junction that creates electron-hole pairs under light, separates them via the built-in field, and produces DC current when connected to a load; each cell gives ~0.5–0.6 V.

## Answer

A solar cell is a p-n junction semiconductor diode (usually silicon) that converts sunlight directly into DC electricity by the **photovoltaic effect**.

1. A silicon wafer has an n-type layer (doped with phosphorus: extra electrons) on top of a p-type layer (doped with boron: extra holes). At the junction, electrons diffuse into the p side and holes into the n side, leaving a **depletion region** with a built-in electric field (about 0.6–0.7 V for silicon).
2. When photons with energy greater than the band gap of silicon (1.1 eV) strike the cell, they create **electron–hole pairs**.
3. The built-in field sweeps electrons towards the n side and holes towards the p side, so the charges separate.
4. With metal contacts on the front (grid) and back, and an external load connected, electrons flow through the load, giving DC current. Photons with less energy than the band gap pass through, and the extra energy of higher-energy photons becomes heat.

```text
   Sunlight (photons)
     | | | |
  ===========  front grid contact
  |  n-type  |   (electrons)
  |----------|   junction / depletion layer
  |  p-type  |   (holes)
  ===========  back contact
      \___[ Load ]___/
         current flow
```
A typical cell gives about 0.5–0.6 V and, under full sun, about 35–40 mA/cm²; cells are connected in series and parallel to make modules.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What does the photovoltaic effect do?
   A. Converts heat to AC electricity via steam
   B. Converts sunlight directly to DC electricity in a p-n junction
   C. Splits water by sunlight
   D. Stores light in a battery
   Answer: B. Photons create electron-hole pairs, separated by the junction field, giving DC current. (Key point: Photovoltaic effect)

2. Which doping makes the n-type and p-type layers in a silicon cell?
   A. Phosphorus for n-type, boron for p-type
   B. Boron for n-type, phosphorus for p-type
   C. Both with phosphorus
   D. Both with boron
   Answer: A. Phosphorus adds extra electrons (n); boron adds holes (p). (Key point: Doping)

3. What happens to photons with energy less than the band gap?
   A. They create double pairs
   B. They heat the cell entirely
   C. They reverse the current
   D. They pass through without creating pairs
   Answer: D. Only photons above 1.1 eV create electron-hole pairs in silicon. (Key point: Sub-gap photons)

## Related in Energy Environment and Society

- [Solar radiation, solar cell and plant](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Asolar-radiation-cell-plant) — Energy Environment and Society, chapter 3
- [Solar cell principle and applications](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Asolar-cell-principle-applications) — Energy Environment and Society, chapter 3
- [Characteristics curve of solar cell](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Asolar-cell-characteristics-curve) — Energy Environment and Society, chapter 3
- [Fuel cell and its working](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Afuel-cell-working) — Energy Environment and Society, chapter 3, asked 2×
- [Solid oxide fuel cell](https://www.bctengineer.com/question.md?key=semester_7%2Fenergy_environment_and_society%3Asofc-construction-working) — Energy Environment and Society, chapter 3, asked 2×

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