Shining Light on Solar Cells - Chapter 3.0: PN Junction Diode (Drift and Diffusion)

In 1954, researchers at Bell Labs in the US discovered pn junction diodes generated a voltage when room lights were on. Within that year, they produced the first commercial solar cell with 6% efficiency (this is the solar cell that we talked about in Chapter 1). This story tells us that a solar cell is essentially a PN Junction with light shining on it!

Hence, it is of utmost importance to first understand the physics of pn junctions without light shining on it, before we move on to solar cells (pn junction with light).

In this chapter, we will learn about:

• How a band diagram of a pn junction looks like.
• How current flows in a pn junction
• The concept of drift and diffusion

Further reference materials that I highly recommend:

ECE Purdue Primer on Semiconductor Fundamentals

A. Kitai, in Principles of Solar Cells, LEDs and Diodes: The Role of the PN Junction, John Wiley & Sons, West Sussex, UK 2011

Other parts in this series:

• Chapter 1: Introduction
• Chapter 2.0: Semiconductor Physics (Band Diagram, Free Carriers)
  • Chapter 2.1: Semiconductor Physics (Doping)
  • Chapter 2.2: Semiconductor Physics (Fermi-Energy Level)