http://www.sciencedirect.com/science/article/pii/S0379677902003983

As was already mentioned by Wilhelm Graupner, there are many methods (yeah, it is nice review paper). Actually, each of them will give you little different result because of sample geometry (and different semiconductor crystallinity) or imperfect approximations. That's a reason why some mobilities are called Hall mobility, OFET mobility, or time-of-flight mobility.

What is the best way? Perhaps direct observation of the charge propagation across the channel of organic field-effect transistor (OFET).

http://www.nature.com/nphoton/journal/v1/n10/abs/nphoton.2007.172.html

However, this method is quite complicated, slow, and extremely expensive.

In your case, you need to know approximate value only and looking for simplest way.

Of course, the simple answer is that it depends on your lab infrastructure and knowledge based. The simplest way is to use what is there and you have good experience. Thus you can look into the paper suggested by Wilhelm Graupner and decide.

If you have technology for OFET fabrication and measurement, than Mir Waqas Alam is right. That's the simplest way. The advantage is that you use well accepted method, since many people are working in the field of OFETs characterizations. The disadvantage? Organic materials usually have different crystallinity (and properties) if you evaporate them on insulating and on conductive surfaces. In addition, the effective mobility includes effect of the contact resistance. This means that electrodes you will use for OFET (e.g. gold) will have different injection energy barrier in comparison with electrode used for OLED (e.g. ITO). Thus, the OFET mobility can be quite different from the mobility in OLED structure. Of course, you can spend some time with study of the contact resistance effect, but you are looking for simple way.

Hence, if you want to fabricate semiconductor film sandwiched between two electrodes, such as OLED structure, than I recommend to measure current-voltage characteristics of your semiconductor in the sandwich structure and use the space-charge limited current (SCLC) condition, i.e. Mott–Gurney law. From the region where current is proportional to the square of the voltage you can estimate the mobility from the slope. Advantage is that you are measuring the sandwiched structure similar to OLED you will fabricate. The disadvantage is that if your organic layer contains too many defects (i.e. charge traps) you may observe more complex current-voltage dependence. It means that it will be not only linearly proportional to voltage (Ohmic region) or proportional to the square of the voltage (SCLC region), but between these two can be region of higher power, so-called trap-free limit (som e voltage when you will fill all traps and over this voltage you reach SCLC region).

Enjoy your experiment and good luck.

Have a nice day,

Martin

@Martin. Thanks for the detailed answer. I have access to OLED fabrication and characterizations. I will try with Mott–Gurney law. However I have come across literature where people are using transient electroluminescence for mobility measurement. How far this method stands. Please suggest.

I have tried capacitance measurement for mobility measurements. Due to some technical reasons I couldnt get the proper data.

Thanks Mir Waqas Alam and Wilhelm Graupner for providing the review papers. Those are very helpful.

Transient EL is useful method, but you need to be little careful. Yes, this method has been suggested for mobility measurement in the past already.

http://link.aip.org/link/doi/10.1063/1.1330766

However, there were various results for the same material used in different OLED structures (i.e. multilayers). Reason is quite simple. The EL is generated after charging of the organic-organic interface and subsequent charge recombination.

http://dx.doi.org/10.1063/1.3277155

It means that you have there contribution from all charge transport layers (electrons as well as holes) and generally it is not possible to say which contribution will be more significant. If the charging of the interface is limited by your investigated material than it is precise enough. If any other layer has comparable or longer transit time the result is not so easy to discuss.

@Martin Weis. Thanks for the suggestions.

For mobility measurements using IV characterizations, is it enough if we sandwich the organic layer between two electrodes? Any reviews available regarding this technique in particular.

This is very old and common approach. The most suitable is a book "current injection in solids" from Lampert and Mark.

Thanks Martin..

I always found it intriguing how a simple property as charge carrier mobility can be so hard to measure - luckily there are great people out there who really share their know how. I recommend the top links of the google search below, as they really mention many of the traps you can fall into.

The basic experiments are rather simple - the art is drawing the right conclusions. And then produce a material a or device that actually reflects the measured and then predicted property :-)

https://www.google.at/search?sourceid=navclient&aq=&oq=charge+carrier+mobility+in+organic+semiconductors+experimental+determination&ie=UTF-8&rlz=1T4RNQN_enAT467AT467&q=charge+carrier+mobility+in+organic+semiconductors+experimental+determination&gs_l=hp....0.0.0.22361...........0.ptrAGMeBivo

@Wilhelm Graupner. Thanks for the link.

Hi there, I read the other answers but you can also use Admittance Spectroscopy to calculate mobilities by fabricating a simple diode (metal/semi-conductor/metal). You can find similar few different methods.

Please check the links down below;

http://oe.phys.hkbu.edu.hk/Mobility%20measurement%20table/

http://oe.phys.hkbu.edu.hk/PosterPPT/MRS_Fall_2005_AS-Poster.pdf

@Nurhan Varal. Thanks for the suggestion and links. I tried that Admittance Spectroscopy. Due to some technical reasons I couldn't calculate it.

Can we use Hall effect as described in fundamental books on semiconductor device physics?

(Time-resolved) Terahertz spectroscopy has been used, with varying levels of success depending on the material system, to make non-contact measurements of the complex AC conductivity (i.e. admittance). The difficulty is usually in interpretation. Metals and Bulk Semiconductors usually obey Drude theory, so the results are easy to model in order to determine a mobility. Many organics are non-Drude like and the interpretation of their complex conductivity in this region is an active area of research. However, single crystalline organic semiconductors (pentacene, rubrene, etc) have shown Drude-like responses similar to metals (see e.g. Ostroverkhova et al PRB v71 p035204 2005); for these materials it may be more straightforward to determine the mobility by this method. The time-resolved part is not necessary so long as the materials is either doped or photoexcited in order for it to become conductive.

When we consider the slop of I vs V^2 we get a value which is a product of mobility and permittivity according to childs law. How to extract the mobility value alone?

Please refer the following paper.

Data Mobility determination using frequency dependence of imagina...

The mobility of the organic compounds can be measured by the time-of-flight (TOF) technique. Here are the some references regarding same:

[1] Article Enabling high-efficiency organic light-emitting diodes with ...

[2] http://pubs.rsc.org/en/content/articlepdf/2017/tc/c7tc03049e

Please see this link

http://www.ung.si/~sstanic/teaching/Seminar/2012/20120521_Raveendra.pdf