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DOE OSTI2020

Materials Data on CdTeO3 by Materials Project

CdTeO3 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Cd2+ sites. In the first Cd2+ site, Cd2+ is bonded in a 6-coordinate geometry to six O2- atoms. There are a spread of Cd–O bond distances ranging from 2.23–2.55 Å. In the second Cd2+ site, Cd2+ is bonded to six O2- atoms to form distorted corner-sharing CdO6 octahedra. The corner-sharing octahedral tilt angles are 72°. There are a spread of Cd–O bond distances ranging from 2.32–2.42 Å. There are two inequivalent Te4+ sites. In the first Te4+ site, Te4+ is bonded in a 3-coordinate geometry to four O2- atoms. There are a spread of Te–O bond distances ranging from 1.90–2.81 Å. In the second Te4+ site, Te4+ is bonded in a 5-coordinate geometry to five O2- atoms. There are a spread of Te–O bond distances ranging from 1.91–2.78 Å. There are six inequivalent O2- sites. In the first O2- site, O2- is bonded in a 4-coordinate geometry to two Cd2+ and two equivalent Te4+ atoms. In the second O2- site, O2- is bonded in a 1-coordinate geometry to one Cd2+ and two Te4+ atoms. In the third O2- site, O2- is bonded in a 3-coordinate geometry to two Cd2+ and one Te4+ atom. In the fourth O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Cd2+ and two equivalent Te4+ atoms. In the fifth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two Cd2+ and one Te4+ atom. In the sixth O2- site, O2- is bonded to three Cd2+ and one Te4+ atom to form distorted corner-sharing OCd3Te tetrahedra.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Materials Data on Al6Cd4TeO12 by Materials Project

Cd4Al6TeO12 crystallizes in the cubic I-43m space group. The structure is three-dimensional. Cd2+ is bonded to one Te2- and three equivalent O2- atoms to form distorted CdTeO3 tetrahedra that share corners with three equivalent CdTeO3 tetrahedra and corners with six equivalent AlO4 tetrahedra. The Cd–Te bond length is 2.82 Å. All Cd–O bond lengths are 2.24 Å. Al3+ is bonded to four equivalent O2- atoms to form AlO4 tetrahedra that share corners with four equivalent CdTeO3 tetrahedra and corners with four equivalent AlO4 tetrahedra. All Al–O bond lengths are 1.77 Å. Te2- is bonded in a tetrahedral geometry to four equivalent Cd2+ atoms. O2- is bonded in a trigonal planar geometry to one Cd2+ and two equivalent Al3+ atoms.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Data for "Gold-Induced Chemical Perturbations in CdTe-Based Photovoltaic Cells"

Back contacting p-type CdTe has been identified as one of the major areas of loss in CdTe photovoltaic (PV) power conversion efficiency (PCE). In research settings, Au is a common contact material due to its ease of use and decent performance. This work provides a detailed investigation into using gold for back contacting As-doped, CdCl2 treated, polycrystalline CdTe that has been exposed to air after absorber processing, another routine practice. First, X-ray photoemission spectroscopy (XPS) is used to determine the native oxide to be 1.6 nm of CdTeO3 using a combination of angle-resolved XPS and the cadmium modified Auger parameter. During gold metallization of CdTe, oxygen and oxidized tellurium are eliminated from the thin CdTeO3 native oxide. The fate of the released oxygen and possibly cadmium and tellurium are not known, but these reaction byproducts can enter the absorber bulk or grain boundaries, stay at the interface, or dissolve in the Au. Interfacial hole barriers between CdTe and Au are measured for samples with and without the native oxide present prior to metallization. Results show that the thin CdTeO3 alleviates the downward band bending by 40 meV from 470 meV to 430 meV even though it is consumed during interface formation. The implications of these chemical reactions on the device are assessed through photoluminescence (PL) spectroscopy which shows losses in internal open circuit voltage (iVoc) from 820 meV to 795 meV, carrier lifetime from 123 ns to 45 ns, and PL quantum yield from 2.9x10-5 to 1.2x10-5. Modeling time-resolved PL lifetimes demonstrates the back surface recombination velocity due to metallization reduces minority carrier lifetimes. These results identify the native oxide and show that it plays an important role in mediating downward band bending along with how the back interface reaction can negatively impact device-scale parameters and reduce PV PCE.

14 SOLAR ENERGY↗

DOE OSTI2023

Oxides related to cadmium telluride solar cells

Polycrystalline cadmium telluride (CdTe) is a leading material in photovoltaic technology due to its high absorption coefficient and near-optimum bandgap of 1.44 eV. It is known that CdTe film processing can promote surface oxidation depending on the growth environment and upon exposure to different oxidation conditions. For example, CdTeO3 forms when the CdTe film is treated in heated dry air, while in humid air, CdTe2O5 is detected. These oxides feature tellurium in the oxidation state +4 compared to the +2 state in CdTe. Other possible relevant oxides are CdO, TeO2, and TeO3. Using hybrid density functional calculations, we studied the electronic structure of these oxide materials and their band alignment to CdTe, which are essential parameters in the characterization of the interfaces at grain boundaries. The goal is to understand their stability and possible effects on passivating grain boundaries. The results are compared to the available experimental data.

14 SOLAR ENERGY↗