Toward metal-organic insulator-semiconductor solar cells, based on molecular monolayer self-assembly on n-Si

Alkyl chain molecules on n-Si were used to test the concept of hybrid metal-organic insulator-semiconductor (MOIS) solar cells. Test structures were made by binding alkyl chain molecules via Si-O-C bonds to oxide-free n-Si surfaces, using self-assembly. With thiol groups at the terminals away from the Si, binding of Au nanoparticles, followed by electroless Au plating yields semitransparent top contacts. First cells give, under 25 mW/ cm² white light illumination, open-circuit voltage V_oc =0.48 V and fill factor FF=0.58. Because with sulfur termination the molecules have a dipole that limits inversion of the Si, we also used methyl-terminated monolayers. Even though then we can work, at this point, only with a Hg top contact, without chemical bond to the molecules, we get, using only radiation (∼AM 1.5) collected around the contact, the expected higher V_oc =0.54 V, and respectable 0.8 FF, justifying further MOIS cell development.