Aqueous-Phase Linker-Assisted Attachment of Cysteinate(2–)‑Capped CdSe Quantum Dots to TiO2 for Quantum Dot-Sensitized Solar Cells

• Published in: ACS applied materials & interfaces 2013-09, Vol.5 (17), p.8649-8654
• Main Authors: Coughlin, Kathleen M, Nevins, Jeremy S, Watson, David F
• Format: Article
• Language: English
• Subjects: Cadmium Compounds - chemistry; Cysteine - chemistry; Quantum Dots - chemistry; Selenium Compounds - chemistry; Semiconductors; Solar Energy; Titanium - chemistry; Water - chemistry
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/am402219e

We have synthesized water-dispersible cysteinate(2–)-capped CdSe nanocrystals and attached them to TiO2 using one-step linker-assisted assembly. Room-temperature syntheses yielded CdSe magic-sized clusters (MSCs) exhibiting a narrow and intense first excitonic absorption band centered at 422 nm. Syntheses at 80 °C yielded regular CdSe quantum dots (RQDs) with broader and red-shifted first excitonic absorption bands. Cysteinate(2–)-capped CdSe MSCs and RQDs adsorbed to bare nanocrystalline TiO2 films from aqueous dispersions. CdSe-functionalized TiO2 films were incorporated into working electrodes of quantum dot-sensitized solar cells (QDSSCs). Short-circuit photocurrent action spectra of QDSSCs corresponded closely to absorptance spectra of CdSe-functionalized TiO2 films. Power-conversion efficiencies were (0.43 ± 0.04)% for MSC-functionalized TiO2 and (0.83 ± 0.11)% for RQD-functionalized TiO2. Absorbed photon-to-current efficiencies under white-light illumination were approximately 0.3 for both MSC- and RQD-based QDSSCs, despite the significant differences in the electronic properties of MSCs and RQDs. Cysteinate(2–) is an attractive capping group and ligand, as it engenders water-dispersibility of CdSe nanocrystals with a range of photophysical properties, enables facile all-aqueous linker-assisted attachment of nanocrystals to TiO2, and promotes efficient interfacial charge transfer.