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  • Holes do not reach their electrodes as fast as electrons

     Japo_Japo updated 1 month, 1 week ago 1 Member · 1 Post
  • Japo_Japo

    Member
    September 10, 2021 at 9:26 pm

    In the solar cell, the perovskite structure rests on a porous layer of titanium oxide which collects the electrons generated under illumination and transports them to the lower electrode. Above the perovskite there is a layer consisting of the organic hole conductor Spiro-OMeTAD, which transports the holes to the upper electrode. “The many different layers in the solar cell are extremely important. They ensure the effective separation of the two charge carriers,” says Rüdiger Berger’s colleague Stefan Weber. ”However, the charge carriers have to overcome a small barrier every time they jump from one material to the other. These barriers act like a construction site on a busy freeway where the vehicles clog. This charge transport jamming in the solar cell leads to losses and thus to a lower efficiency.”

    In several test series, the researchers found that a strong accumulation of positive charges takes place in the perovskite layer upon exposure to light. They suppose that the reason for this positive charging is that the titanium dioxide electron conductor works much more effectively than the hole conductor. The holes do not reach their electrode as fast as the electrons and accumulate on the way. The excess of positive charges in the perovskite layer then generates an opposing electric field which slows down the charge transport even further.

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