arXiv subjects

Behrang H. Hamadani

Publications and source records attributed to Behrang H. Hamadani.

3 recordsLinked to original sources

arXiv2025

Origin of the voltage gap and recombination losses in all-perovskite tandem solar cells

All-perovskite tandem solar cells with narrow and wide bandgap perovskite absorbers are promising candidates for low-cost and high efficiency photovoltaic applications. However, the open circuit voltage of typical tandem structures is generally smaller than the sum of the individual voltages in the single-junction form; a quantity we call the voltage gap. Subcell optimization can only begin once nonradiative losses associated with each absorber layer can be properly identified. To address this, we used absolute electroluminescence hyperspectral imaging to construct external radiative efficiency maps of each subcell within the tandem stack and compare these measurements with single junction devices. These measurements were then combined with additional electro-optical characterization and modeling to construct subcell current vs voltage curves. We find that the narrow band gap subcell contributes the most towards the voltage gap and therefore fabrication and processing efforts should focus on reducing nonradiative recombination losses within the narrow band gap absorber.

physics.optics↗

arXiv2025

Comparison of Electroluminescence and Photoluminescence Imaging of Mixed-Cation Mixed-Halide Perovskite Solar Cells at Low Temperatures

Halide perovskites have emerged as promising candidates for high-performance solar cells. This study investigates the temperature-dependent optoelectronic properties of mixed-cation mixed-halide perovskite solar cells using electroluminescence (EL) and photoluminescence (PL) hyperspectral imaging, along with current-voltage analysis. Luminescence images, which were converted to EL and PL external radiative efficiency (ERE) maps, revealed significant changes in the optoelectronic behavior of these devices at low temperatures. Specifically, we found that a significant source of heterogeneity in the low-temperature EL ERE maps below 240 K is related to local charge injection and extraction bottlenecks, whereas PL ERE maps show suppressed non-radiative recombination and significant improvements in efficiency throughout the investigated temperature range. The spatial distribution of ERE and its variation with applied current were analyzed, offering insights into charge-carrier dynamics and defect behavior. Our results reveal that while the perovskite layer exhibits enhanced ERE at low temperatures, charge injection barriers at the interfaces of the perovskite solar cells significantly suppress EL and degrade the fill factor below 240 K. These findings reveal that a deeper understanding of the performance of perovskite solar cells under low-temperature conditions is an essential step toward their potential application in space power systems and advanced semiconductor devices.

cond-mat.mtrl-sci↗

arXiv2025

Accurate Performance Characterization, Reporting, and Benchmarking for Indoor Photovoltaics

Indoor photovoltaics (IPVs) provide a promising solution for powering Internet-of-Things smart devices, which has led to a surge in IPV research. However, the diverse lighting scenarios adopted in IPV studies pose unique challenges in characterization, reporting, and benchmarking, which may obscure genuine performance improvements and result in inaccurate conclusions due to characterization errors. This study provides a comprehensive, quantitative analysis of these challenges, investigating them through the experimental characterization of IPVs covering a broad performance parameter space, including c-Si, a-Si:H, perovskite, and organic devices. We reveal that many of these challenges can lead to unacceptable error levels in IPV performance parameters, with the angular interplay among the test light source, measuring device, and IPV being particularly detrimental under diffuse indoor illumination. To address these characterization challenges, we evaluate practical protocols to mitigate them. We additionally analyze different benchmarking protocols, revealing the strengths of the reference-cell method and the limitations and solutions related to the indoor spectral coincidence concept. To facilitate the implementation of these findings, we provide comprehensive characterization, reporting, and benchmarking checklists. By enabling reliable performance evaluation and benchmarking, we anticipate that our analyses and guidelines will stimulate further advancements in IPVs, facilitating the realization of their full potential.

physics.app-ph↗