Adding to what has been said by Morteza,

Transparent conducive films for optoelectronic deceives in general and solar cells in particular must satisfy some basic requirements:

- Their transmittance must be as high as possible for the incident solar radiation ,

- Their sheet resistance must be as small as possible,

- They must be mechanically rigid and adhere well to the substrata and the active cell material 

- They must  withstand and be stable,  against the environment 

- They must form a proper MS contact with the overlaying layer of the cell

From my point of view the most powerful candidate is ITO till now and may be in the near future. It is well experienced. The others have time to prove their qualifications provided that the thin film properties not only depend on the materials but also their fabrication condition.

It depends to your required properties. CNT based thin films show high mechanical robustness and transparency. However, they suffer from low sheet resistance. Therefore, very high quality CNTs through CVD method is needed to get low sheet resistance. Graphene based electrodes show high transparency with low sheet resistance. But they are not very robust to mechanical deformation. Ag nanowire based electrodes show poor mechanical robustness and low environmental stability. Therefore, it depends to your target application to work with which one. 

We could considerably improved the stability of Ag nanowire electrodes by Ni core shell structure. Check our recent paper:

https://www.researchgate.net/publication/263393150_AgNi_CoreShell_Nanowire_Network_for_Robust_Transparent_Electrodes_Against_Oxidation_and_Sulfurization?ev=prf_pub

Article Ag@Ni Core–Shell Nanowire Network for Robust Transparent Ele...

Adding to what has been said by Morteza,

Transparent conducive films for optoelectronic deceives in general and solar cells in particular must satisfy some basic requirements:

- Their transmittance must be as high as possible for the incident solar radiation ,

- Their sheet resistance must be as small as possible,

- They must be mechanically rigid and adhere well to the substrata and the active cell material 

- They must  withstand and be stable,  against the environment 

- They must form a proper MS contact with the overlaying layer of the cell

From my point of view the most powerful candidate is ITO till now and may be in the near future. It is well experienced. The others have time to prove their qualifications provided that the thin film properties not only depend on the materials but also their fabrication condition.

Dear Amjadi 

Many thanks for your time and useful suggestions. It  depends to the target application to work with which one. I wonder whether the composite of the the alternatives could solve the problems.

Regards

Miao

Dear Zekry

I really appreciate the advice you have given.Although ITO is viewed as the most powerful candidate , the increasing price ,complicated fabrication requirements and brittleness problems of ITO still need to be considered.I just wonder  whether the composite of the the alternatives could solve the problems.

Regards

Miao

If flexibility is a feature of the device, then it is valid to look for alternatives, they might have an edge over ITO. Otherwise, ITO has the best transparency vs conductivity characteristic until now, hence, it is hard to replace it. 

Dear Hussam Qasem ,  in my opinion,flexible transparent conductive electrode is  essential in the future technological innovation.

Miao, 

Recently, many researchers have used organic sources with aromatic rings in therir structures like PAN to make carbon nanosheets which have similar properties to graphene. and they have used them in many applications such as electrodes for solar cells and transistors.. You could take a look at this paper. The process is usually easy and straight forward...  However, the substrate is usually not big size and flexible. I hope my answer is helpful.

Al doped Zn oxide is one possible option. keep watch on publication from our group to know a cheap and easy method for production of the same. 

Dear Souri

  Thanks for your useful suggestions.The paper that you provided is very interesting and i have read it carefully.Solid carbon as graphene precursors is a very intersting and significat object.This process is much more simple than CVD method.

Regards

Miao

Dear Chakraborty

 Thanks for your useful advices.ZnO is a promising alternative to ITO and many researches have conformed that.I have read several publications from your group and i am very intrerested in your work.

Regards

Miao

The performance in terms of transparency and conductivity of PEDOT-based films has increased significantly in recent years. The following paper shows how the conductivity of PEDOT:PSS films increases to >100 S/cm when treated with dimethyl-sulfate, while preserving high optical transparency in the visible regime: 

http://pubs.acs.org.offcampus.lib.washington.edu/doi/abs/10.1021/jp107386x

Which alternative to ITO is better for you depends on the needs for your specific application, as has been pointed out above in this thread. However, if flexibility is a desired property, films based on organic electronic polymers should be among the main candidates, especially as they are easy to produce over large areas. In the context of avoiding ITO, I want to point you to this item in Nature Photonics, discussing various strategies for doing exactly that: 

http://www.nature.com.offcampus.lib.washington.edu/nphoton/journal/v5/n4/full/nphoton.2011.46.html 

http://pubs.acs.org.offcampus.lib.washington.edu/doi/abs/10.1021/jp107386x

http://www.nature.com.offcampus.lib.washington.edu/nphoton/journal/v5/n4/full/nphoton.2011.46.html