Semiconductor
Nanocrystals as Luminescent Down-Shifting Layers To Enhance the Efficiency
of Thin-Film CdTe/CdS and Crystalline Si Solar Cells
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Abstract
A simple optical model is presented
to describe the influence of a planar luminescent down-shifting layer
(LDSL) on the external quantum efficiencies of photovoltaic solar
cells. By employing various visible light-emitting LDSLs based on
CdTe quantum dots or CdSe/CdS core–shell quantum dots and tetrapods,
we show enhancement in the quantum efficiencies of thin-film CdTe/CdS
solar cells predominantly in the ultraviolet regime, the extent of
which depends on the photoluminescence quantum yield (PLQY) of the
quantum dots. Similarly, a broad enhancement in the quantum efficiencies
of crystalline Si solar cells, from ultraviolet to visible regime,
can be expected for an infrared emitting LDSL based on PbS quantum
dots. A PLQY of 80% or higher is generally required to achieve a maximum
possible short-circuit current increase of 16 and 50% for the CdTe/CdS
and crystalline Si solar cells, respectively. As also demonstrated
in this work, the model can be conveniently extended to incorporate
LDSLs based on organic dyes or upconverting materials