What we have are Voc and Jsc . We know D can be expressed in:
L=(Dt)1/2
where, L is diffusion length, D is diffusion coefficient and t is carriers life time
or
J=qD(dn/dx)
where, J is current density from diffusion, q is elementary charge, (dn/dx) is charge carriers density gradient.
in some expressions like the following expression, we already must clarify some factors like, G(generation rate) to get the correct diffusion length:
Voc=2kT/q Ln(GLt/ni )
kT : product of Boltzmann constant and temprature
GL : Generation rate
ni : Intrinsic density of charge carriers
Therefore, using this expression, we would not be able to approach directly to the diffusion coefficient!
Dear Sabah,
There are many methods to determine D experimentally. You can measure the mobility mu by the time of drift method and then calculate the mobility. Then using Einstein relation
D= Vt x mu where Vt is the thermal voltage = k T/q with the symbol have their usual meaning.
If you have a solar cell or diode, you can measure the open circuit voltage decay from which you can determine the life time of the minority carriers. Then if you measure the reverse saturation current I0, then you can calculate from it the diffusion coefficient since
I0= A q D ni^2/ ND L, where A is the area of the diode, D the diffusion constant, L the diffusion length, ni is the intrinsic castration and ND is the doping concentration. Knowing ND , ni and the area A , then one can calculate D.
If you inspect the list of my publications in my profile you find methods to measure the diffusion length and lifetime.
wish you success
Thank you Dr. Zekry for your nice and detailed answer. Since, first we have to know ND and ni, in the case of applying new materials (in a dye-sensitized solar cell), how it is possible to get these parameters? What do you think, is required to have a better and more dependable results of leakage current?
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