Theory of analyzing free energy losses in solar cells

Abstract

We make up the free energy balance for thermalized electrons and holes in a solar cell. Equations for the loss rates of free energy due to recombination and transport of carriers are derived. The well known expression for Joule heat dissipation also holds for the free energy loss by diffusive transport. All loss rates have units of mW/cm2. Thus transport losses become directly comparable in magnitude to recombination losses. The latter are usually quantified in mA/cm2 rather than mW/cm2. The impact of various loss mechanisms on the power output of the cell, also in mW/cm2, becomes directly apparent.