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I always thought a solar cell consists of two areas, a n-type and a p-type doped one. So what exactly is meant by n-type doped solar cells? Does it not have a p-type doped area? And how does it work then? How would I get the recombined p-n area that lies in between, then, or is it not crucial for the solar cell to work?

Furthermore, I always thought that the "majority charge carrier" is independently defined for the p and the n type area, not for the whole solar cell, how does one even establish a good conductivity with only 1 doping type?

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  • $\begingroup$ When the Fermi level is exactly in the middle of the bandgap, i.e. $E_F = 1/2(E_c-E_v)$ then you have an intrinsic semiconductor, meaning equal density of conduction band electrons $n_0$ and free valence band holes $p_0$, or usually written as $n_0 = p_0 = n_i,$ (i for intrinsic) As you dope the semiconductor (i.e. increase one type of carriers), the latter turns into an inequality, e.g. $n_0>n_i>p_0$ for n-doped. So n-doped simply means the majority of carriers are electrons and not holes. $\endgroup$
    – Ellie
    Aug 31, 2015 at 22:34
  • $\begingroup$ But do i not dope n type as well as p type ? Like i said does a solar cell not consist of two different doped areas ? What is the sense of having far more electrons than "holes", shouldn't the conductivity be determined by the lower amount of charge carriers? $\endgroup$
    – user85397
    Aug 31, 2015 at 22:39
  • $\begingroup$ @Mareck can you provide a reference of where this n-type only solar cell comes from? In principle it is possible because electric field is not needed for photovoltaic action. Only a way of selecting the carrier types on extraction is needed. However, minority carriers (the holes in n-type materials) will have short lifetime so efficiency may not be great. $\endgroup$
    – boyfarrell
    Sep 1, 2015 at 7:23

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The expression "n-type solar cell" refers to cells for which n-type silicon wafers are used. The starting material (Si feedstock) for producing n-type silicon wafers is the same as the one used for p-type Si crystals. The difference is in the doping process during crystallization: while for p-type Si, group III dopants (e.g. Boron) are used, for n-type Si crystals Group V dopants (e.g. Phosphorous) are used.

In a typical semiconductor, there might be $10^{17}~\mathrm{cm^{-3}}$ majority carriers and $10^6~\mathrm{cm^{-3}}$ minority carriers. In n-type semiconductors, the majority carriers are Negatively charged electrons whereas in p-type semiconductors, the majority carriers are Positively charged holes.

N-type does not refer to a semiconductor with 1 doping but to the negatively charged majority carriers.

N-type silicon has a better tolerance to common impurities, e.g. Fe, and potentially results in higher minority carrier diffusion lengths compared to p-type substrates with a similar impurity concentration. Moreover, n-type Si does not suffer from the boron-oxygen related light-induced degradation LID.

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