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Probing carrier dynamics below the surface of solar cells
Optically probed the charge carrier lifetime below the surface of solar materials using two-photon (2P) time-resolved PL mapping, and demonstrated that the traditional one-photon (1P) technique can underestimate the bulk lifetime in CdTe by 10x.
Significance and Impact
Improving carrier lifetime is a critical component in boosting solar cell efficiencies, but accurately measuring the bulk carrier lifetime is one of the greatest challenges in evaluating solar materials. 2P tomography can non-destructively map bulk lifetime, surface recombination and other properties within photovoltaic materials to locate areas of reduced device performance.
- Current optical techniques such as 1P photoluminescence probe the surface of solar cells where surface defects can hide true bulk lifetime.
- 2P optical excitation allows excitation below the surface of the sample and thus enables non-destructive measurement of bulk properties.
- Multidimensional maps of lifetime and emission spectra were created. 3D lifetime tomography is now possible and currently under development.
E. S. Barnard, E. T. Hoke, S. T. Connor, J. R. Groves, T. Kuykendall, Z. Yan, E. C. Samulon, E. D. Bourret-Courchesne, S. Aloni, P. J. Schuck, C. H. Peters & B. E. Hardin. Scientific Reports 2013 3, 2098.