Nano-organized Hybrid Materials with Higher Charge Generation for Solar Cell Applications

Bis(dithiocarbamate) molecules were reacted with (hexadecylamine/stearate)-capped CdSe nanocrystals (NCs) (7.5 nm diameter) to form multilayers on ITO glass via layer-by-layer alternation. Pump-Probe and Photocurrent investigations were performed. Pump-Probe data reveal that the replacement of the bulky surface ligands, capping CdSe-NCs, by bis(dithiocarbamate) molecules strongly enhances the charge generation efficiency of the films. Compared with the multilayers produced with bis(carboxylate) linkers of comparable length and structure, the effect is particularly marked when 1, 4 - phenylenebis-(dithiocarbamate) is employed. The data are in accordance with the just reported record photocurrent responses of the bis(dithiocarbamate) based multilayers. The presence of charged-trapped state population, located close to the NCs surface is revealed. The relaxation of the hole into this hybrid state is a fundamental first step in the separation of the photo-excited charges, as required in any photo-voltaic process