Electrical Characteristics of Solar Cells

Abstract

To understand the behaviour of a solar cell as an electric power source, let us review the familiar characteristics of p-n junction diode and its behaviour under forward and reverse bias when dark. When n-type silicon semiconductor (characterized by electrons as majority carriers and holes as minority carriers) is in metallurgical contact with a piece of p-type semiconductor (characterized by holes as majority carriers and electrons as minority carriers) the boundary formed is p-n junction (Fig. 6.1). Owing to the process of natural diffusion electrons would flow from regions of high concentration (n-type) to the regions of low concentration (p-type) and the similar diffusion for holes. The electrons leaving the n-type side will expose positive charges in n-type side. The holes leaving the p-type side will expose the negative charges. This will result in a charge imbalance on both sides; it will set up an electric field that will oppose the natural diffusion tendency of electrons and holes and an equilibrium situation will be obtained. The region of transition is known as depletion layer, because the region is depleted of holes and electrons. The diode behaviour of such a p-n junction in dark conditions for forward bias and reverse bias conditions is well known and is shown in Fig. 6.2.