Light-trapping enhancement in thin film solar cells with photonic crystals

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Zhou, Dayu
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Rana Biswas
Gary Tuttle
Vikram Dalal
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Electrical and Computer Engineering

The Department of Electrical and Computer Engineering (ECpE) contains two focuses. The focus on Electrical Engineering teaches students in the fields of control systems, electromagnetics and non-destructive evaluation, microelectronics, electric power & energy systems, and the like. The Computer Engineering focus teaches in the fields of software systems, embedded systems, networking, information security, computer architecture, etc.

The Department of Electrical Engineering was formed in 1909 from the division of the Department of Physics and Electrical Engineering. In 1985 its name changed to Department of Electrical Engineering and Computer Engineering. In 1995 it became the Department of Electrical and Computer Engineering.

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  • Department of Electrical Engineering (1909-1985)
  • Department of Electrical Engineering and Computer Engineering (1985-1995)

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Photovoltaics (or solar cell) has been an active area for research and development, driven by the world's constantly increasing needs for power. Among the current solar technologies, thin film solar cell promises lower cost, but at the expense of lower power conversion efficiency. The efficiency of thin film solar cell can be improved using light confinement schemes commonly referred to as light-trapping. In this thesis, we develop novel light-trapping schemes utilizing photonic crystals (PCs). The optical modeling is performed with a rigorous scattering matrix approach, where Maxwell's equations are solved in Fourier space, and simulations are carried out on parallel computation environment. Although the concepts apply to any thin film solar cell structures, hydrogenated amorphous silicon (a-Si:H) single junction thin film solar cell is used for simulation due to widely available optical property data.;In the solar cell structure we design, a one dimensional (1D) photonic crystal or distributed Bragg reflector (DBR) is used as back reflector. The DBR consists of alternating layers of SiO2 and Si or Indium Tin Oxide (ITO) and Si to provide high reflectivity with little loss. A layer of two dimensional (2D) photonic crystal slab between the a-Si:H absorber layer and the DBR can diffract light at oblique angles, so that total internal reflection can occur inside the absorber layer. The light path length inside the absorber layer will be greatly increased, so will the absorption. The parameters for photonic crystals are optimized through computer simulations to obtain the maximum absorption and path length enhancement. The simulations show significantly enhanced photon harvesting between 600--775 nm below the band edge. The path length enhancement can reach several hundred at resonant peaks, far exceeding the classical limit predicted for randomly roughened scattering surfaces.

Tue Jan 01 00:00:00 UTC 2008