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Pn junction in solar cell case

  1. Nov 21, 2008 #1
    HI. I got some question about the derivation of the I-V characteristic in a solar cell.
    The first step is to solve the minority carrier diffusion equation with appropriate boundary conditions: at the edges of the cell and at the edges of the depletion zone.
    At the edges of the d.z. the conditions for the concentrations p_N and n_P can be found using quasi-Fermi levels....

    1) Suppose to be in case of forward applied voltage V. In the quasi neutral regions, far from the d.z, and into the d.z., the quasi-Fermi levels are constant. This means that here currents J_p and J_n equal to 0. How is it possible to have currents just in teh little spaces out of the d.z. when a votage is applied?

    2) Why qV= F_n - F_p ?

    In thee next step of the derivation, they integrate the electron continuity equation over the d.z. ,
    dJn/dx = q[ R(x) - G(x)]
    with R recombinatio rate ad G generation.
    For R they consider just midgap single level trap mechanism. They keep a point Xm inner the d.z. at wich p(xm)=n(xm) and then consider R(xm) for the whole d.z.

    3) Does is exst a point xm where p=n?

    If someone would like to answer id be really glad. Bye
  2. jcsd

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