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.

Schematic representation of the interference of Pu(iv) in the voltammetric determination of U in a mixed U–Pu solution in 1 M H2SO4.

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