# Numerical Modeling of Crystalline Silicon Solar Sells

Research Projects for Undergraduate Stundets.

Modeling of silicon solar cell is a complex task, which involves using of different simulation tools and techniques. Generally speaking, silicon solar cell is a semiconductor device, the operation of which is governed by the set of drift-diffusion equations. The solution of these equations gives the performance of the cell, i.e. the amount of solar energy it can convert into electricity, as well as lots of other useful information.

In fact, to simulate solar cells engineers use the same kind of tools they use to simulate transistors for CPUs and memory. However, there are two important differences. The first is that silicon solar cell is a large scale device, with the area of tens of centimeters, while the dimensions of modern transistors are usually described in nanometers. And because the larger the device, the more equations the computer has to solve, it turns out that modern computational power is not enough to simulate the entire solar cell. This is the reason, why the cell is divided into unit domains, which are solved in a numerical simulator. The solutions of the unit domains are further combined into a circuit to simulate the entire solar cell. The second difference is that the model of a solar cell has to consider not only electrons and holes interacting with the crystal, external bias and each other, but also photons, which come from the Sun and bring their energy to excite the carriers inside the cell. Because optical excitation is a reach process, engineers usually use a separate tool to model it and then load the results of this simulation into the device simulator.

Thus, the overall process can be split into three separate parts: simulation of optical generation, simulation of a unit domain of the solar cell and circuit simulation, where the circuit mimics the entire solar cell.

## Project 1. Optical simulation of silicon solar cells

The goal of the first project is to learn the optical ray tracer Sunrays in order to simulate optical generation rate for different silicon solar cell structures. Sunrays is a sophisticated program designed to trace the path of each ray from the solar spectrum in order to figure out the position inside the cell, where it will be absorbed and will give birth to electron-hole pair. The range of structures will include the cells textured with upright pyramids, covered with various antireflection coatings, having different thicknesses and different metal and dielectric layers on the rear side.

## Project 2. Circuit simulations for silicon solar cells

The goal of the second project is to create a Spice model of a solar cell, where the current-voltage characteristics of previously simulated unit domains are combined in one big circuit taking into account the series resistance of the front and rear metallization and edge effects. Prerequisites: knowledge of circuit simulation tools.

**To apply, please, send email to Stas Herasimenka (sherasim at asu.edu). Write a couple of words about yourself and why would you like to do research at Solar Power Lab.**