Date of Award

Fall 2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Applied Physics - (Ph.D.)

Department

Physics

First Advisor

N. M. Ravindra

Second Advisor

Bhushan L. Sopori

Third Advisor

Anthony Fiory

Fourth Advisor

Tao Zhou

Fifth Advisor

Martin Schaden

Sixth Advisor

Ken Keunhyuk Ahn

Abstract

Proper optical designing of solar cells and modules is of paramount importance towards achieving high photovoltaic conversion efficiencies. Modeling softwares such as PV OPTICS, BIRANDY and SUNRAYS have been created to aid such optical designing of cells and modules; but none of these modeling packages take the front metal electrode architecture of a solar cell into account.

A new model, has been developed to include the front metal electrode architecture to finished solar cells for optical calculations. This has been implemented in C++ in order to add a new module to PV OPTICS (NREL’s photovoltaic modeling tool) to include front metallization patterns for optical design and simulation of solar cells. This new addition also calculates the contribution of light that diffuses out of the illuminated (non-metallized) regions to the solar cell current. It also determines the optical loss caused by the absorption in the front metal and separates metallic losses due to front and back contacts. This added capability also performs the following functions:

  • calculates the total current that can be generated in a solar cell due to optical absorption in each region, including the region beneath the front metal electrodes for the radiation spectrum of AM 1.5,
  • calculates various losses in the solar cell due to front electrode shading, metal absorption, and reflectance,
  • makes a plot of how light is absorbed in the metal as well as silicon under the shaded region in the solar cell.

Although Finite Difference Time Domain (FDTD) is the numerical technique of choice to solve Maxwell’s equations for a propagating electromagnetic wave, it is both time consuming and very demanding on the computer processors. Furthermore, for complicated geometric structures, FDTD poses various limitations. Hence, ray tracing has been chosen as the means of implementing this new model.

This new software has been used to carry out a detailed investigation on the effect of various parameters of the front electrode architecture on the performance of alkaline anisotropically texture etched (100) oriented single crystal silicon solar cells. These parameters include:

  • the thickness of the silicon absorber layer,
  • the texture height,
  • width of the front metal fingers,
  • height of the front metal fingers, and
  • the effect of encapsulation of a solar cell in a module.

The results show that the front metal architecture used in commercial silicon solar cells has minimal effect on its performance. A decline in the total current derived from the cell encapsulated in a module is also observed. This has helped to narrow down the design variables of commercial silicon solar cells with the standard front electrode grid of fingers and busbars to only the electrical transport.

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