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Optical and microstructural properties of as-deposited CdTe films deposited on soda lime glass by magnetron sputtering at various source flux angles have been investigated using GIXRD, SEM, unpolarized transmittance / reflectance, and spectroscopic ellipsometry. Influence of deposition angle on resultant crystalline grain size and orientation are tracked for these films. All CdTe films studied are found to have cubic crystal structure and (111) preferential grain orientation. Films deposited at 0° and 45° are almost entirely (111) oriented, whereas films deposited at higher angles exhibit a wider variety of competing grain orientations, suggesting that deposition angle can be used as an effective parameter towards controlling grain orientation. With increasing numbers of grain orientations, grain size is found to decrease. Ex-situ spectroscopic ellipsometry is used to obtain the structural and optical properties. Stress induced in the film is calculated based on shifts of critical point energies.
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Crystal reorientation in methylammonium lead iodide perovskite thin film with thermal annealing
While there has been rapid progress in the performance of perovskite solar cells, the details of film formation, effect of processing parameters and perovskite crystal structure are still under discussion. The details of the X-ray diffraction (XRD) pattern of the tetragonal phase of CH 3 NH 3 PbI 3 perovskite existing at room temperature are often overlooked, with unresolved (002) (at 2 θ = 13.99° for CuK α and q = 0.9927 Å −1 ) and (110) (at 2 θ = 14.14° and q = 1.003 Å −1 ) peaks considered to be one peak at 14°, leading to an inaccurate estimation of lattice parameters. In this study, we use an electrospray deposition technique to prepare perovskite films at room temperature, oriented in (002) and (110) directions, with (002) as the preferred orientation. The results of a detailed study on the emergence of the two orientations during perovskite formation are reported. The effect of process parameters, such as substrate temperature during deposition and annealing temperature, on the grain orientation was established using XRD and grazing incidence wide angle X-ray scattering (GIWAXS). The study suggests that an irreversible crystal reorientation from (002) to (110) occurs at high temperature during rapid annealing, whereas a reversible crystal thermal expansion is seen during slow annealing. Finally, the results of the grain reorientation are correlated with the film properties, and it is shown that the film with the dominant (110) orientation has improved morphology and optoelectronic properties. The detailed structural investigation and characterization presented in this study are important for the precise determination of crystal orientation and achievement of desirable photovoltaic properties of the absorber material by carefully observing the adjacent crystal plane peaks in the XRD pattern of the perovskite thin films.
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- Award ID(s):
- 1806147
- PAR ID:
- 10150223
- Date Published:
- Journal Name:
- Journal of Materials Chemistry A
- Volume:
- 7
- Issue:
- 20
- ISSN:
- 2050-7488
- Page Range / eLocation ID:
- 12790 to 12799
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/C9TA02358E
