Why does increased surface area of a semi-conductor lead to better properties?

[LogicX]

I'm researching solar cells, some of which use TiO₂ as a semiconducting film. Modern solar cells use TiO₂ nanoparticles to increase the surface area of the film. Somehow this is advantageous to the solar cell.

From my limited understanding of semiconductors, I know that to get a current flowing in a solar cell, an electron has to be excited from the valence band to the conduction band. The simple concept of a metallic conductor is of a "sea" of electrons. Wouldn't having nanoparticles adversely effect the flow of electrons between TiO₂ molecules? Because now they are more separate crystals instead of being one continuous crystal lattice.

I'm not sure how surface area helps semiconductors. Does it allow more electron excitation? Does more light get absorbed because the material has higher surface area? This would only make sense to me if it was true that light absorption could only take place at the edges of a crystal lattice. Is that true?

Is there better electron transfer to other films in the solar cell? If electron injection from the semiconductor to the dye is dependent on surface area, I can can see this as being the reason why it would help to have large surface area.

Thanks.

 

[Valerie Park]

The added surface area of the TiO2 nanoparticles can indeed be advantageous to solar cells. The increased surface area allows for a greater number of electrons to be excited into the conduction band, which increases the flow of current in the solar cell. The increased surface area also allows for more light to be absorbed by the TiO2 film. Photons of light can be absorbed at the edges of a crystal lattice, and having more edges due to the nanoparticles increases the light absorption. Furthermore, the increased surface area provides a greater amount of contact between the TiO2 film and other components of the solar cell, such as the electron-injecting dye, which helps facilitate the electron transfer process.