Quantum Dot Solar Cells. Harvesting Light Energy with CdSe Nanocrystals Molecularly Linked to Mesoscopic TiO₂ Films

TLDR

Visible light excitation of CdSe QDs injects electrons into TiO₂ nanocrystallites, but significant electron loss occurs due to scattering, charge recombination at TiO₂/CdSe interfaces, and internal TiO₂ grain boundaries. CdSe QDs are assembled onto mesoscopic TiO₂ films via bifunctional surface modifiers (SH‑R‑COOH), and the injected charge carriers are collected at a conducting electrode to generate photocurrent. Femtosecond transient absorption and emission quenching confirm electron injection from excited CdSe QDs into TiO₂ nanoparticles, with thermally relaxed s‑state transfer rates ranging from 7.3 × 10⁹ to 1.95 × 10¹¹ s⁻¹, and the TiO₂‑CdSe photoanode achieves a photon‑to‑charge carrier generation efficiency of 12%.

Abstract

By using bifunctional surface modifiers (SH-R-COOH), CdSe quantum dots (QDs) have been assembled onto mesoscopic TiO(2) films. Upon visible light excitation, CdSe QDs inject electrons into TiO(2) nanocrystallites. Femtosecond transient absorption as well as emission quenching experiments confirm the injection from the excited state of CdSe QDs into TiO(2) nanoparticles. Electron transfer from the thermally relaxed s-state occurs over a wide range of rate constant values between 7.3 x 10(9) and 1.95 x 10(11) s(-1). The injected charge carriers in a CdSe-modified TiO(2) film can be collected at a conducting electrode to generate a photocurrent. The TiO(2)-CdSe composite, when employed as a photoanode in a photoelectrochemical cell, exhibits a photon-to-charge carrier generation efficiency of 12%. Significant loss of electrons occurs due to scattering as well as charge recombination at TiO(2)/CdSe interfaces and internal TiO(2) grain boundaries.