The Balance of Thermodynamic Potentials in Solar Cells Investigated by Numerical Device Simulations

This article presents an extension of the classical gain/loss analysis of Brendel et al. based on the balance of free energy in a solar cell. We consider the full balance of all thermodynamic potentials by separating the excess free energy into excess chemical and excess electrostatic potentials. A layer-by-layer analysis of an exemplary silicon solar cell shows that the different functionalities of different parts of the solar cell, e.g., the neutral base and the space charge regions, are well reflected in the different pictures provided by looking at the thermodynamic potentials separately. Additionally, we investigate fill factor losses by insufficient majority carrier collection at the back contact of the solar cell with two prototypical passivation layers. Here we show that resistive losses, i.e., losses in the electrostatic potential can be distinguished from kinetic losses, i.e., losses in the chemical potential.