Local
Electronic Structure Changes in Polycrystalline CdTe with CdCl<sub>2</sub> Treatment and Air Exposure
Morgann Berg
Jason M. Kephart
Amit Munshi
Walajabad S. Sampath
Taisuke Ohta
Calvin Chan
10.1021/acsami.7b18963.s001
https://acs.figshare.com/articles/journal_contribution/Local_Electronic_Structure_Changes_in_Polycrystalline_CdTe_with_CdCl_sub_2_sub_Treatment_and_Air_Exposure/5972386
Postdeposition CdCl<sub>2</sub> treatment of polycrystalline CdTe is known to increase the
photovoltaic device efficiency. However, the precise chemical, structural,
and electronic changes that underpin this improvement are still debated.
In this study, spectroscopic photoemission electron microscopy was
used to spatially map the vacuum level and ionization energy of CdTe
films, enabling the identification of electronic structure variations
between grains and grain boundaries (GBs). In vacuo preparation and
inert transfer of oxide-free CdTe surfaces isolated the separate effects
of CdCl<sub>2</sub> treatment and ambient oxygen exposure. Qualitatively,
grain boundaries displayed lower work function and downward band bending
relative to grain interiors, but only after air exposure of CdCl<sub>2</sub>-treated CdTe. Analysis of numerous space charge regions at
grain boundaries showed an average depletion width of 290 nm and an
average band bending magnitude of 70 meV, corresponding to a GB trap
density of 10<sup>11</sup> cm<sup>–2</sup> and a net carrier
density of 10<sup>15</sup> cm<sup>–3</sup>. These results suggest
that both CdCl<sub>2</sub> treatment and oxygen exposure may be independently
tuned to enhance the CdTe photovoltaic performance by engineering
the interface and bulk electronic structure.
2018-03-12 13:21:05
GB trap density
ambient oxygen exposure
photovoltaic device efficiency
CdTe photovoltaic performance
grain boundaries
CdCl 2 treatment
oxide-free CdTe surfaces
spectroscopic photoemission electron microscopy
Local Electronic Structure Changes
space charge regions
Air Exposure Postdeposition CdCl 2 treatment
CdCl 2 Treatment