Engineered CuInSe<sub><i>x</i></sub>S<sub>2–<i>x</i></sub> Quantum
Dots for Sensitized Solar
Cells
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Abstract
Colloidal CuInSe<sub><i>x</i></sub>S<sub>2–<i>x</i></sub> quantum dots (QDs) are an attractive less-toxic
alternative to PbX and CdX (X = S, Se, and Te) QDs for solution-processed
semiconductor devices. This relatively new class of QD materials is
particularly suited to serving as an absorber in photovoltaics, owing
to its high absorption coefficient and near-optimal and finely tunable
band gap. Here, we engineer CuInSe<sub><i>x</i></sub>S<sub>2–<i>x</i></sub> QD sensitizers for enhanced performance
of QD-sensitized TiO<sub>2</sub> solar cells (QDSSCs). Our QD synthesis
employs 1-dodecanethiol (DDT) as a low-cost solvent, which also serves
as a ligand, and a sulfur precursor; addition of triakylphosphine
selenide leads to incorporation of controlled amounts of selenium,
reducing the band gap compared to that of pure CuInS<sub>2</sub> QDs.
This enables significantly higher photocurrent in the near-infrared
(IR) region of the solar spectrum without sacrificing photovoltage.
In order to passivate QD surface recombination centers, we perform
a surface–cation exchange with Cd prior to sensitization, which
enhances chemical stability and leads to a further increase in photocurrent.
We use the synthesized QDs to demonstrate proof-of-concept QDSSCs
with up to 3.5% power conversion efficiency