Dear Abdus,

I am not sure the ligand chain length can affect much on Voc of your solar cells. But, in my case, I am working on NP also. The ligand chain length affect on the different energy level. Typically, longer chain gives higher Voc but Jsc is lower and it is vice versa. 

Hope this wil help you.

Good luck.

Dear Abdus,

Welcome,

The effect of the nano gold particles mechanism is they scatter light and thereby increasing the optical path length in the active layer and thereby more absorption of the incident photons of the suitable wavelength. The second effect that it helps to dissociate the the generated  excitations where they when polarized by the suitable wavelength of the incident radiation.  So any type of legend which which detracts the exciton dissociation function will reduce the collection efficiency   of the photgenrated carriers and consequently reduce the photo current. The highest efficiency will be achieved by direct contacting the gold nano particles to the donor absorber from the side of the hole collecting layer. If you coat the gold nano particles with the donor absorber  as a legend, then the solar cells work slightly better than the direct inclusion of the gold particles.

As for the length of the legend from the same donor active material you can not increase the length of the legend as the electrons dissociated by the gold particles must be transported through the absorber layer to the donor acceptor interface. This means that the thickness of the donor active layer is limited by the transport process of electrons and holes. They will recombine with each other if  they diffuse a distance larger than the diffusion length.

The open circuit voltage improvement is a consequence of increasing the photcurrent by harvesting more light in the presence of the gold nanoparticles.

For more information please follow the paper in the link:  https://www.academia.edu/23826827/Plasmonic_bulk_heterojunction_solar_cells_The_role_of_nanoparticle_ligand_coating?auto=download

Best wishes

Thank you Abdelhalim Zekry