1.3. The p-n Junction Solar Cell
The planar p-n junction solar cell under low injection is usually singled out for special analysis since realistic approximations exist that allow analytic solutions to be developed and used successfully for the description of practical devices. The success of this model is due, to a large extent, to the clear way the cell can be divided into three regions—emitter, junction region, and base—that serve a different purpose in solar cell operation.
The emitter and the base—which remain largely neutral during the cell operation—absorb the main part of the incident light and transport the photogenerated minority carriers to the junction. The p-n junction—which contains a strong electric field and a fixed space charge—separates the minority carriers that are collected from the emitter and the base. The junction is effectively devoid of mobile charge carriers and is sometimes called the depletion region.