2. Synthesis of Ternary Cadmium Chalcogenides
Hot Injection Method
Se + S
(in TOP)
Thermocouple
CdSe
CdS
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
3. Photophysical Properties
Absorption Spectra Emission Spectra
Photographs of QDs dispersed in
Under UV light illumination toluene under UV light illumination
Band gap can be tuned
without changing the size of
the ternary QDs
4. 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 QDSCs are assembled in sandwich fashion
driven towards an Cu2S-Reduced graphene oxide (RGO) used
electrode by applying as counter electrode
a potential
Aqueous polysulfide solution used as
electrolyte
5. Quantum Dot Solar Cell (QDSC)
h 2.0% 2.4% 2.8%
CdSeS
Increasing Se:S
With decreasing band gap, the power conversion efficiency goes up.
This is due to absorption of light at higher wavelength
6. Quantum Dot Solar Cell (QDSC)
Can we still improve the efficiency?
Possibly a new design!
Sequential vs. Mixed
EPD has the ability to load QDs sequentially
by choosing different solutions
h (%)
Expt. Calc.
Green + Red 2.49 1.91
Orange + Red 3.20 2.27
Green + Orange + Red 3.00 1.87
Green, Orange and Red (mixed) 2.34 2.21
7. Quantum Dot Solar Cell (QDSC)
Two possible mechanism for the synergistic enhancement
Electron Transfer Energy Transfer
Detailed time-resolved spectroscopic experiments are in progress
to investigate the synergy
8. Conclusions
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
Acknowledgements
Division 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!
