Synthesis of Ternary Cadmium ChalcogenidesHot 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
Photophysical PropertiesAbsorption 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
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
Quantum Dot Solar Cell (QDSC) h 2.0% 2.4% 2.8% CdSeS Increasing Se:SWith 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. 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
Quantum Dot Solar Cell (QDSC)Two possible mechanism for the synergistic enhancement Electron Transfer Energy TransferDetailed time-resolved spectroscopic experiments are in progressto investigate the synergy
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 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!