I want to know how exactly the hole mobility can be calculated from Mott-Gurney law, specifically perovskite solar cell structure like ITO/PEDOT: PSS/PEROVSKITE/Al?
Does anyone have a clear idea and relevant experience in perovskite for hole mobility measurments?
Dear Azmat,
There is a discussion within the research gate forum. Please see the following link:
https://www.google.com/amp/s/www.researchgate.net/post/What_exactly_is_space_charge_and_what_are_some_example_of_what_it_is2/amp
To be clear, the single carrier hole only device structure of a semiconductor has to be the work function of electrodes close to the valence band (HOMO energy level for organic) of a semiconductor. In your case, the device structure of a perovskite should be ITO/PEDOT:PSS/Perovskite/MoOx/Au. If you use the device structure that you mentioned with Al as an electrode, the electrons likely inject into the device too, so it wouldn't be a hole only device. It would be a great idea to test both device structures. You will find at high voltages driven devices that the device with Aluminium electrode will emit light. Counterpart device with MoOx/Au will be no light emitted. This also prove whether it is a single carrier device or not. In the past, we came cross many publications which claimed single carrier devices. In fact, it is not! You can imagine the the calculation of such carrier mobility wouldn't make sense.
Hope it helps.
Xuhua
Dear Azmat,
welcome!
The mobility is defined for free charge carriers in the material. It is so that when one applies an electric field on a material with free holes or electrons such free carriers will drift under the electric field such the charge carriers will acquire a steady state velocity called drift velocity vd which is proportional to the applied electric field E such that vd= mu E, where mu is the mobility of the charge carrier.
The mobility mu depend on may factors:
- Lattice vibration because of the temperature of the material
- The presence of impurities and crystallographic defects
- The presence of grain boundaries
In case of polycrysatlline material, the grain boundaries may dominate the mobility of the free charge carriers.
So, i think the best way to get the the mobility is by measuring its value. One of the most used method is the time of flight method and the I-V characteristics or the small signal impedance measurements.
For measuring the semiconductor parameters please follow the paper: Method Measuring the semiconductor parameters
Best wishes
Dear Azmat,
Prof. Hamza brought the relation between the the current J and the voltage for trap free space charge limited current. In order to extract the mobility from this relation you must be sure that such conduction mechanism is valid. This is verified by plotting log J vs log V this must be a staight line with slope 2 which is the exponent of the voltage V. In order to determine mu from the such plot you have to know L and epsilon of the material.
This is one precaution.
The other is that you prepare the device such that the perovskite material is supplied with ohmic contacts such that the applied voltage will be dropped on the perovskite material. So the above structure may be not suitable for measuring mu. For the discussion of this issue please follow the link: https://www.researchgate.net/post/How_is_the_current_limited_in_metal_organic_semiconductor_metal_MOSM_diode
So, in summary, you can determine mu from the MJ law but you have to worry about its validation.
Best wishes
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