Postdeposition 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 work, 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. Finally, 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.
Berg, Morgann, et al. "Local Electronic Structure Changes in Polycrystalline CdTe with CdCl<sub>2</sub> Treatment and Air Exposure." ACS Applied Materials and Interfaces, vol. 10, no. 11, Mar. 2018. https://doi.org/10.1021/acsami.7b18963
Berg, Morgann, Kephart, Jason M., Munshi, Amit, Sampath, Walajabad S., Ohta, Taisuke, & Chan, Calvin (2018). Local Electronic Structure Changes in Polycrystalline CdTe with CdCl<sub>2</sub> Treatment and Air Exposure. ACS Applied Materials and Interfaces, 10(11). https://doi.org/10.1021/acsami.7b18963
Berg, Morgann, Kephart, Jason M., Munshi, Amit, et al., "Local Electronic Structure Changes in Polycrystalline CdTe with CdCl<sub>2</sub> Treatment and Air Exposure," ACS Applied Materials and Interfaces 10, no. 11 (2018), https://doi.org/10.1021/acsami.7b18963
@article{osti_1441464,
author = {Berg, Morgann and Kephart, Jason M. and Munshi, Amit and Sampath, Walajabad S. and Ohta, Taisuke and Chan, Calvin},
title = {Local Electronic Structure Changes in Polycrystalline CdTe with CdCl<sub>2</sub> Treatment and Air Exposure},
annote = {Postdeposition 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 work, 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. Finally, 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.},
doi = {10.1021/acsami.7b18963},
url = {https://www.osti.gov/biblio/1441464},
journal = {ACS Applied Materials and Interfaces},
issn = {ISSN 1944-8244},
number = {11},
volume = {10},
place = {United States},
publisher = {American Chemical Society (ACS)},
year = {2018},
month = {03}}