Composition and size dependent band
gap engineering with longer
excited state charge carrier lifetime assist CdS
x
Se1–x
alloy semiconductor
quantum dots (QDs) as a promising candidate for quantum dot solar
cell (QDSC). Colloidal CdS
x
Se1–x
alloy QDs were synthesized using the hot injection
method where a stoichiometric mixture of S-TOP and Se-TOP were injected
at 270 °C in a mixture of Cd-oleate. The electron decoupled from
hole in the alloyed structure due to delocalization of electron in
electronically quasi type-II graded CdS
x
Se1–x
alloyed structure. As a
result, intraband electron cooling time increases from 100s of fs
to sub 10 ps time scale in the alloyed graded structure. Extremely
slow electron cooling time (∼8 ps) and less charge recombination
(∼50% in >2 ns) as compared to both CdS and CdSe QDs are
found
to be beneficial for charge carrier extraction in QD solar cells.
Using polysulfide electrolyte and Cu2S-deposited ITO glass
plates as photocathode, the efficiency of the QD solar cell was measured
to be 1.1 (±0.07)% for CdS, 3.36 (±0.1)% for CdSe, and 3.95
(±0.12)% for CdS0.7Se0.3 QDs. An additional
nonepitaxial CdS quasi-shell followed by ZnS passivation layer (TiO2/ CdS0.7Se0.3 /quasi-CdS/ZnS) was deposited
on top of the CdS0.7Se0.3 film which showed
a photo current conversion efficiency (PCE) of 4.5 (±0.18) %.
The overall 14% increase of PCE is due to the quasi CdS shell helps
to separate more electrons through passivating the surface states
of TiO2.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.