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Niraj Shrestha1 Corey R. Grice1 Geethika Liyanage1 Adam Phillips1 Michael Heben1 Yanfa Yan1 Randy Ellingson1

1, The University of Toledo, Toledo, Ohio, United States

It has been previously reported that use of a CdSexTe1-x window layer increases the short-circuit current density (Jsc) of a CdTe solar cell by increasing the cell photo-response for both short- and long wavelength photons. However, open-circuit voltage (VOC) and fill factor (FF) are frequently lower than for traditional CdS/CdTe solar cells. One possible reason behind lower VOC and FF relates to increased recombination losses within or at the interfaces of the CdSexTe1-x region of the device. Because the use of CdSexTe1-x is relatively new for the CdTe solar cell technology, we focus here on characterization of native and impurity defects as a basis for understanding the performance in CdSexTe1-x/CdTe solar cells. Low temperature photoluminescence (PL) spectra have been measured for CdSexTe1-x (x = 0.00, 0.08, 0.14, 0.21, 0.29, 0.36 and 0.44) films. CdSexTe1-x films used in this study were prepared via a co-sputtering process using CdSe and CdTe targets. Tauc plots and room temperature steady-state PL measurement of these films confirm the band gap bowing in CdSexTe1-x films with bowing parameter, b = 0.81 ± 0.03. The lowest band gap energy of ~1.394 eV is achieved for at x ≈ 0.36. X-ray diffraction measurements show that the lattice constant of the CdSexTe1-x film decreases linearly with Se content. Time resolved PL measurement reveals that photogenerated carrier lifetime increase monotonically with Se content, indicating that the narrowed bandgap region of the absorber may, unlike CdS, contribute to the cell’s photocurrent as has been observed experimentally. Temperature dependent and laser power dependent PL together with time resolved PL will be carried out to explore the sources of observed defects. In addition, PL and TRPL analyses will be reported for CdTe deposited by close-space sublimation onto sputtered CdSe thin films.

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