  Doping of bulk semiconductors has revealed widespread success in
optoelectronic applications. In the past few decades, substantial effort has
been engaged for doping at the nanoscale. Recently, doped zero-dimensional
quantum dots made of semiconductor nanocrystals have been demonstrated to be
promising materials for luminescent solar concentrators (LSCs) as they can be
engineered for providing Stokes-shifted tunable emission in the solar spectrum.
However, existing doped colloidal quantum dots suffer from moderately low
quantum efficiency and intrinsically small absorption cross-section, which
together fundamentally limit their effective usage. Here, we show the first
account of copper doping into two-dimensional atomically flat CdSe colloidal
quantum wells. Copper doping via post-synthesis partial cation exchange into
3-5 monolayers of CdSe and CdSe/CdS core-shell colloidal quantum wells (CQWs)
enables Stokes-shifted, tunable dopant induced highly efficient
photoluminescence emission having high quantum efficiencies (>43%), accompanied
by an order of magnitude higher absorption cross-section than that of the doped
quantum dots. Based on these exceptional properties, we demonstrated a flexible
prototype luminescent solar concentrators using these newly synthesized doped
colloidal quantum wells. These findings may open up new directions for
deployment of CQWs in LSCs for advanced solar light harvesting technologies.
