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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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39 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Dual-Wavelength Time-Resolved Photoluminescence Study of CdSe x Te 1-x Surface Passivation via Mg y Zn 1-y O and Al 2 O 3

Voltage loss is currently one of the biggest challenges facing cadmium telluride (CdTe) based photovoltaics. Determining the location(s) of major voltage loss within the device stack (e.g., front/back interface, grain boundaries) is therefore of primary interest. Here, we present a custom-built time-resolved photoluminescence system with two excitation wavelengths - 670 (standard) and 405 nm - to probe the device stack at depths of approximately 130 and 35 nm, respectively; their comparison helps differentiate interface and bulk contributions to carrier lifetime. We apply this system to examine the passivation effect of two significant recent advances in CdTe: the incorporation of Se to form graded CdSe x Te 1-x and the replacement of CdS with Mg y Zn 1-y O. It is found that x = 0.2 Se is required to obtain lifetime improvements, primarily in the bulk. Additionally, evidence for trapping at the Mg y Zn 1-y O/CdSe x Te 1-x interface was observed. Furthermore, this indicates further work is required to sufficiently passivate the front interface.

CdSeTe↗
DOE OSTI2024

Improved VOC in RbF-Treated Cu(In,Ga)Se2 Solar Cells via Passivation of Recombination Centers

Cu(In,Ga)Se 2 (CIGS) solar cells have benefited in recent years from the addition of heavy alkali elements, such as Rb, which increase the solar cell open-circuit voltage ( V OC ). To investigate the source of this improvement, here, we compare samples with and without Rb to perform a quantitative comparison of electronic defects and minority carrier lifetime. Deep-level transient and optical spectroscopy measurements were performed on two sets of rubidium fluoride (RbF)-treated and untreated CIGS, and three distinct traps were identified regardless of RbF treatment. The RbF treatment was found to reduce the concentration of the H2 trap, which was previously found to act as a recombination center and is located preferentially at CIGS grain boundaries. Time-resolved photoluminescence measurements showed an increase in effective lifetime after RbF and nearly all lifetime improvement resulted from reductions in bulk recombination. The observed V OC improvement is well correlated with increased minority carrier lifetime and acceptor concentration, which led to increases and decreases in electron and hole quasi-Fermi levels, respectively.

Cu(In Ga)Se2 (CIGS)↗
DOE OSTI2020

Field Effect in CdSeTe/CdTe Solar Cells with Biased Spectroscopy

Steady-state and time-resolved photoluminescence measurements were performed under external electrical bias on thin polycrystalline CdSeTe/CdTe solar cells. The results indicate that internal field effects which can go unnoticed during traditional, unbiased spectroscopy measurements may be more consequential than generally realized. In addition, probing the field behavior with bias may allow investigation of defect states and the determination of transport characteristics, such as mobility.

14 SOLAR ENERGY↗