Imaging local luminescence variations in CdSe0.1Te0.9 thin films grown by the colossal grain growth process

• Published in: Cell reports physical science Vol. 4; no. 8; p. 101522
• Main Authors: Neupane, Ganga R., Winchester, Andrew J., Peraca, Nicolas Marquez, Albin, David S., Duenow, Joel N., Reese, Matthew O., Pookpanratana, Sujitra J., Thon, Susanna M., Hamadani, Behrang H.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16.08.2023; Elsevier
• Subjects: CdSeTe; donor-acceptor pair recombination; external radiative efficiency; grain boundary; grain interior; hyperspectral imaging; photoelectron emission microscopy; PL quenching; rate-equation model; SOLAR ENERGY; thin films; rate-equation model; grain boundary; donor-acceptor pair recombination; external radiative efficiency; photoelectron emission microscopy; CdSeTe; grain interior; hyperspectral imaging; thin films; PL quenching
• ISSN: 2666-3864; 2666-3864
• DOI: 10.1016/j.xcrp.2023.101522

Clear visualization and understanding of luminescence properties of grain interiors and grain boundaries in polycrystalline thin-film photovoltaic materials are crucial to achieving high-performance solar cells. Luminescence-based measurements, for example, reveal sub-bandgap energetic disorder or impurity-related radiative transitions in these materials, and when performed in the absolute scale, they can show the extent of voltage-limiting non-radiative recombination. Here we use a hyperspectral imaging technique to investigate inter- and intra-grain photoluminescence variations in polycrystalline CdSe0.1Te0.9 films made by the colossal grain growth process. We observe that grain boundaries show higher luminescence than grain interiors for all energies below the bandgap energy. Multiple distinct sub-bandgap defect transitions are detected and determined to be related to donor-acceptor pair impurities. A comparison of the excitation-intensity-dependent photoluminescence at the grain boundaries with grain interiors suggests that carrier concentration is higher at grain boundaries. This finding is supported by photoemission electron microscopy imaging of the films, showing ≈70 meV upward energy shift in the band structure at the grain boundaries. Finally, we investigate a dramatic thermal quenching behavior related to the donor-acceptor pairs luminescence over a temperature range and use a rate-equation model to attribute it to the sudden redirection of the radiative recombination channels to non-radiative channels with increasing temperature. [Display omitted] •CdSeTe thin films have a non-uniform local structure and charge carrier recombination•PL imaging reveals sub-bandgap energetic disorder, impurity DA-type transitions•PEEM confirms an upward band bending at the grain boundaries•PL thermal quenching was observed at both grains and grain boundaries Visualizing and studying local charge carrier recombination phenomena in polycrystalline thin films is crucial for a better understanding of factors that limit the PCE of solar cells. Here, Neupane et al. investigate the luminescence properties of grain boundaries and grain interiors and the local band structure in CdSeTe films grown by the CGG process.