am7b18963_si_001.pdf (1.53 MB)
Local Electronic Structure Changes in Polycrystalline CdTe with CdCl2 Treatment and Air Exposure
journal contribution
posted on 2018-03-12, 13:21 authored by Morgann Berg, Jason M. Kephart, Amit Munshi, Walajabad S. Sampath, Taisuke Ohta, Calvin ChanPostdeposition CdCl2 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 CdCl2 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 CdCl2-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 1011 cm–2 and a net carrier
density of 1015 cm–3. These results suggest
that both CdCl2 treatment and oxygen exposure may be independently
tuned to enhance the CdTe photovoltaic performance by engineering
the interface and bulk electronic structure.
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GB trap densityambient oxygen exposurephotovoltaic device efficiencyCdTe photovoltaic performancegrain boundariesCdCl 2 treatmentoxide-free CdTe surfacesspectroscopic photoemission electron microscopyLocal Electronic Structure Changesspace charge regionsAir Exposure Postdeposition CdCl 2 treatmentCdCl 2 Treatment
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