Introduction
The goal of this homework is to understand the design trade-offs and interactions in a solar cell. A simple design can be done using the closed form diode equations, but calculations of the optical properties and short circuit require computer calculations, and hence we will use the solar cell PC1D design program to calculate the solar cell efficiency. Your starting point will be the cell described in the file: Basic_Solar_Cell.prm available in the PC1D directory.
Note that for the PC1D files, you may not vary any of the parameters in PC1D, except as
specified in the project. As output, save the PC1D *.prm files in the PC1D directory. Please make sure to name the *.prm files such that they can be readily identified when we look for them, and note in your report what they are called. When you have finished the project, copy and save the entire PC1D directory to another, higher level directory labeled with you name, and submit it.
It is well understood that the light source would be an intensity of 100 mW/cm2 with AM1.5G spectrum. Characterization is done at 25oC.
Part 1: Closed Form Equations vs computer calculations
Calculate Jo, Jsc (using the constant generation approximation in your notes) and Voc for the parameters in the cell.prm file you'll generate or with those of the cell described in the Basic_Solar_Cell.prm. Compare calculated Jo, Jsc and Voc with those obtained using PC1D. How close are they, and what accounts for the differences? Change the emitter doping profile in PC1D to a Gaussian and repeat the comparison.
Part2: Emitter Optimization
Using the parameters in Basic_Solar_Cell.prm assume a Gaussian emitter profile, design and change the emitter doping and thickness to modify the emitter sheet resistance between 60 and 200 ?/square. The minimum emitter thickness is 0.2 microns.
a) What are the emitter parameters that lead to maximum efficiency? Physically explain your results and justify why the maximum occurs at the values it does. Check the impact of the emitter sheet resistance on the resistive loss using PVlighthouse calculator.
b) Investigate the impact of the front surface recombination velocity on the result in a). How does it change if Sfront is varied from 100 cm/s to 105 cm/s. Explain physically and check your physical explanation using PC1D.
Part 3: Back Surface Field
To reduce the effects of a rear recombination velocity, a back surface field (BSF) is implemented, consisting of a thin heavily diffused region at the rear of the solar cell. Include a BSF into PC1D, and do an optimization for the thickness and doping. The maximum BSF thickness is 3 microns.
a) What are the optimum BSF parameters? Physically explain the trade-offs in the BSF
design.
b) From the energy band diagram or a solar cell with a back surface field, explain how
the surface passivation works.
Part 4: Base doping, thickness and minority carrier lifetime
The base doping is initially set to 1 Ohm-cm material, which is a typical value for a
commercial solar cell.
a) Change the base doping concentration (resistivity) and determine the optimum base doping from PC1D simulations with dopant dependent lifetime model turned-on.
c) Change the base thickness and determine its impact on the cell parameters.
d) Check the impact of the coupled base thickness-back surface recombination velocity on the cell parameters.
Part 5: Surface texturing and ARC
Apply surface texturing and optimize antireflection coating to get the maximum short circuit current and efficiency
Part 6
Wrap up your results and for the optimum cell design provide:
1. The cell parameters
2. The cell I-V-P characteristics under illumination
3. The cell external quantum efficiency
4. The cell spectral response
5. The cell dark I-V characteristics