Introducing a 1D numerical model for the simulation of PN junctions of varying spectral material properties and operating conditions

Abstract

During the last years, innovative concepts of solid-state devices, such as multi-junction solar cells and thermophotovoltaic converters, have emerged as efficient means of direct electricity production. The accurate estimation of the conversion efficiency of such devices using simple yet effective numerical tools is a necessity to optimize their performance. This work presents an in-house code, which is based on the Drift Diffusion Model to simulate p-n junction diodes, under equilibrium (bias voltage application) and non-equilibrium (bias voltage and device illumination) conditions. Under non-equilibrium, illumination can originate from either solar radiation (conventional photovoltaic cell) or a thermally heated emitter (thermophotovoltaic operation). The drift-diffusion and Poisson’s equations are solved using a one-dimensional (1D) finite element Petrov-Galerkin method based on piecewise nonlinear interpolants of second-order accuracy, while the total current is evaluated in a post-process manner using the Scharfetter-Gummel scheme. Initially, the model is verified against the freeware SimWindows. Later on, a parametric analysis on the photovoltaic cell design and operating conditions reveals that its efficiency is highly affected by its total length, the n-type sub-region width, the doping levels of both p and n regions, the semiconductor material type, and, the device’s operating temperature. In contrast to other solvers, this one takes into account the model parameters’ dependence on temperature and electromagnetic spectrum, while it can be extended to incorporate the thermally stimulated electron emission in thermionic-based devices and 2D spatial effects. Finally, the calculated conversion efficiencies can be used to build a Reduced Order Model that can be further coupled with a computational fluid dynamics model to evaluate the overall thermo-electric performance of a solid-state device.