Driving forces and charge-carrier separation in p-n junction solar cells

While p-n junction solar cells have long been established as the dominant solar-cell technology in the market, the origin of the charge-carrier separation in these devices remains open to debate. It is often attributed to the built-in electric field that exists across the junction in thermodynamic equilibrium, although this interpretation can lead to physical inconsistencies. In this work we present an interpretation approach based on the analogy between a solar cell and a generalized electric source model. Our interpretation is given through a detailed analysis of the electric potential and the non-electric chemical potential across each device, which are plotted together in complete potential diagrams introduced for this purpose. We demonstrate that the driving force separating the free charge carriers in both devices originates from the change of the non-electric chemical voltage that happens once the device is brought out of thermodynamic equilibrium. This change, therefore, can be interpreted as the driving force that triggers the selective motion of charge carriers and, thus, induces the electric voltage at the terminals of the device.