The p-n junction is the most fundamental component of a solar cell. In fact, a p-n junction diode alone can act as a primitive photovoltaic device, because its internal electric field separates light generated electron-hole pairs. With the ideal diode equation now understood, we can begin to analyze p-n junction diode behavior in both the dark and in light; these behaviors are called the "dark characteristics" and the "illuminated characteristics", respectively.
The dark characteristics of p-n junction diode are based on the ideal diode principles we have already explored. Therefore, our analysis of dark characteristics will center on circuit applications. The illuminated characteristics will also be based on ideal diode principles, but will have the added feature of a light-induced current (photocurrent).
i-v characteristic for an ideal diode. Image from Wikimedia Commons.