CdSe quantum-dot-sensitized solar cell with ∼100% internal quantum efficiency.

We have constructed and studied photoelectrochemical solar cells (PECs) consisting of a photoanode prepared by direct deposition of independently synthesized CdSe nanocrystal quantum dots (NQDs) onto a nanocrystalline TiO(2) film (NQD/TiO(2)), aqueous Na(2)S or Li(2)S electrolyte, and a Pt counter electrode. We show that light harvesting efficiency (LHE) of the NQD/TiO(2) photoanode is significantly enhanced when the NQD surface passivation is changed from tri-n-octylphosphine oxide (TOPO) to 4-butylamine (BA). In the PEC the use of NQDs with a shorter passivating ligand, BA, leads to a significant enhancement in both the electron injection efficiency at the NQD/TiO(2) interface and charge collection efficiency at the NQD/electrolyte interface, with the latter attributed mostly to a more efficient diffusion of the electrolyte through the pores of the photoanode. We show that by utilizing BA-capped NQDs and aqueous Li(2)S as an electrolyte, it is possible to achieve ∼100% internal quantum efficiency of photon-to-electron conversion, matching the performance of dye-sensitized solar cells.