Solution-processed transparent electrodes

A thin-film solar cell technology requires a transparent electrode to extract one type of charge. Typically, transparent conductive metal oxides (such as indium-tin-oxide or zinc-oxide)  are used for this purpose. However, this approach has a number of disadvantages:

• Metal oxides are deposited by sputtering process. The limited throughput results in a high cost per square meter. This especially a problem for thin-film technologies that are projected to be very low cost such as organic solar cells.
  
• Metal oxides are brittle. When deposited on a flexible substrate, the metal oxide will crack when the substrate is bent to a small radius, resulting in device failure.
• The performance of metal oxides, i.e. their optical transparency for a given sheet resistance, is limited.
  

We have developed a solution-processable transparent electrode that has none of the disadvantages listed above. Figure 1 shows the performance of our transparent electrode and compares it to indium-tin-oxide and carbon nanotube mesh electrodes. As far as we know, the electrodes we've developed are the best available.

Fig. 1: Solar transmissivity (averaged for wavelengths between 300nm-2um and weighted with the AM1.5 solar spectrum) as a function of sheet resistance for a typical ITO electrode (red line), carbon nanotube meshes (open triangles), and our solution processed electrode (filled squares). [Edited because of IP considerations.]

Our future work will focus on further lowering the sheet resistance without affecting the optical transparency. Our models show that a 10-fold improvement in sheet resistance is possible.

Project info

• People: Jung-Yong Lee and Peter Peumans
• Collaborators: Yi Cui's group
• Contact: Peter Peumans