J. Am. Chem. Soc., 2013, 135, 877

Synthesis of Ternary Cadmium Chalcogenides

Hot Injection Method

Se + S(in TOP)

Thermocouple

CdSeCdS

Gradient Structure:Formed due to higher reactivity of Se towards Cd compare to S

By changing the composition, i.e., Se to S ratio, the band gap of QDs can be tuned easily

Absorption Spectra Emission Spectra

Band gap can be tuned without changing the size of

the ternary QDs

Under UV light illumination

Photophysical Properties

Photographs of QDs dispersed in toluene under UV light illumination

Quantum Dot Solar Cell (QDSC)

Loading of QDs to mesoporous TiO2 film: Electrophoretic Deposition (EPD)

QDs are generally negatively charged in solution and can be driven towards an electrode by applying a potential

QDSCs are assembled in sandwich fashion Cu2S-Reduced graphene oxide (RGO) used

as counter electrode Aqueous polysulfide solution used as

electrolyte

CdSeS

Increasing Se:S

h 2.0% 2.4% 2.8%

With decreasing band gap, the power conversion efficiency goes up. This is due to absorption of light at higher wavelength

Quantum Dot Solar Cell (QDSC)

Can we still improve the efficiency? Possibly a new design!

Sequential vs. MixedEPD has the ability to load QDs sequentially

by choosing different solutions

Expt. Calc.Green + Red 2.49 1.91Orange + Red 3.20 2.27Green + Orange + Red 3.00 1.87Green, Orange and Red (mixed) 2.34 2.21

h (%)

Quantum Dot Solar Cell (QDSC)

Electron Transfer Energy Transfer

Two possible mechanism for the synergistic enhancement

Detailed time-resolved spectroscopic experiments are in progress to investigate the synergy

Quantum Dot Solar Cell (QDSC)

Highly luminescent ternary chalcogenides with gradient structure offers a new way to design QDSCs

EPD helps in forming layer-by-layer structure within mesoscopic TiO2 film, thus maximizes the light harvesting capability

Sequential ordering of higher-band-gap QDs followed by lower-band-gap QDs provides a better synergy for harvesting photons across visible spectrum

Conclusions

AcknowledgementsDivision of Chemical Sciences, Geosciences, and Biosciences, Office of Basic Energy Sciences, Office of Science, United States Department of Energy through Grant DE-FC02-04ER15533

Thank you for your attention!