Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 11, Issue 13, Pages 13003-13010Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsami.9b00835
Keywords
cadmium telluride; tin oxide; photovoltaics; X-ray photoelectron spectroscopy; interfaces; passivation; solar cells
Funding
- U.S. Department of Energy (DOE) [DE-AC36-08G028308]
- U.S. Department of Energy Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Office [30307]
- U.S. Department of Defense Office of Naval Research
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Interfaces at the front of superstrate CdTe-based solar cells are critical to carrier transport, recombination, and device performance, yet determination of the chemical structure of these nanoscale regions has remained elusive. This is partly due to changes that occur at the front interfaces during high temperature growth and substantive changes occurring during postdeposition processing. In addition, these buried interfaces are extremely difficult to access in a way that preserves chemical information. In this work, we use a recently developed thermomechanical cleaving technique paired with X-ray photoelectron spectroscopy to probe oxidation states at the SnO2 interface of CdTe solar cells. We show that the tin oxide front electrode promotes the formation of nanometer-scale oxides of tellurium and sulfur. Most oxidation occurs during CdCl2/O-2 activation. Surprisingly, we show that relatively low-temperature anneals (180-260 degrees C) used to diffuse and activate copper acceptors in a doping/back contact process also cause significant changes in oxidation at the front of the cell, providing a heretofore missing aspect of how back contact processes can modify device transport, recombination, and performance. Device performance is shown to correlate with the extent of tellurium and sulfur oxidation within this nanometer-scale region. Mechanisms responsible for these beneficial effects are proposed.
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