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I am looking at device architecture of planar heterojunction solar cell. What I understand from reading "Planar heterojunction organometal halide perovskite solar cells: roles of interfacial layers" (Kim, 2015) is that the perovskite can basically act as a charge carrying material, and thus mesoporous TiO2 is not needed to transport charge carriers to the anode. However, in the below structure, as well as in Kim, 2015, they mention the presence of PEDOT:PSS and PCBM as electron and hole transporting materials, resulting in p-i-n architecture. But if perovskite can conduct electrons to and from the electrodes by itself, what is the function of those two layers in the cell?

Thank you!

Right side: Perovskite solar cell (Planar heterojunction) architecture

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  • $\begingroup$ Is the problem to reconduct organic solar cell and perovskite etc solar cells in the well clear contest of established solar cell. The architecture at right can be seen as a donor acceptor heterojunction among electrodes.I think you could search for articles by Gregg. I learned some obvious point from him. $\endgroup$
    – Alchimista
    Dec 14, 2017 at 12:27
  • $\begingroup$ pubs.acs.org/doi/abs/10.1021/jp022507x $\endgroup$
    – Alchimista
    Dec 14, 2017 at 12:31

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The two structures you mentioned are n-i-p and p-i-n. The perovskite active material can generate electrons and holes, and it is also capable of transporting them to electrodes. But what is the driving force? The answer is the electric field created internally because of the band alignment that n and p layers create. They also function as hole blocking and electron blocking layers, respectively. Back to your question. p and n layers are providing the driving force of charge transport.

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As it is rightly pointed out in an earlier answer that N and P layers offer a driving force for the carrier transport, I would like to bring a side advantage of these layers into the notice - The perovskites are prone to degradation by moisture. These N and P layers apart from rendering better charge extraction may also provide protection of the perovskite layer from possible moisture entry and metal diffusion from contacts that hamper the PV performance of the cell.

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