Diffusion-Recombination Impedance Model for Solar Cells with Disorder and Nonlinear Recombination

The diffusion–recombination model is a key tool in understanding the photovoltaic operation of solar cells. Dye-sensitized solar cells, organic solar cells, and inorganic semiconductor solar cells are systems affected by disorder that are often characterized with impedance spectroscopy. In this paper, we extend the previous theory of diffusion–recombination impedance including traps and nonlinear recombination. We show the transmission line equivalent circuit representation, and we describe the physical meaning of a number of model parameters that can be obtained: the chemical capacitance, ; the recombination resistance, ; the transport resistance, ; the electron lifetime, ; the electron conductivity, ; the chemical diffusion coefficient of electrons, ; and the diffusion length, . At most, three of these parameters are independent, but if the diffusion length is short, the impedance model collapses to a function that has one degree of freedom less, known as the Gerischer impedance. We show the connection of the two parameters that remain to the diffusion length and the lifetime