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Band-to-band photoluminescence (PL) imaging is one of the experimental techniques widely used to assess non-radiative recombination rates at a fixed incident light intensity. Minority carrier lifetimes in semiconductors such as mc-Si are also affected by optical injection levels. These can be measured by transient photoconductance (TPC). In this paper, PL imaging of shunts and TPC lifetime results for incident intensities of up to 50 Suns are compared for multiple samples of mc-Si. 

This paper discusses our experimental results obtained for several p-type polycrystalline Si wafers using transient photoconductance decay method in combination with a numerical model that accounts for the carrier density dependence of recombination lifetime. Using peak illumination intensities of up to 65 Suns, we are able to estimate the recombination rates for the various carrier recombination mechanisms separately. The model with such realistic recombination parameters produces a realistic diffusion length of minority carriers in Si at high optical injection. Our approach can be applied to the characterization of semiconductor materials for concentrator photovoltaics as well as to design of optoelectronic devices. 

This paper describes and discusses several recent faculty-student research activities at Lincoln University (PA), an HBCU. Specifically, it makes connections between NSF-sponsored faculty research and the projects that several undergraduate Engineering Science and Physics students have been working on. The Engineering Science is a relatively new major at Lincoln. New research experiences are particularly useful, so integrated learning is an attractive methodology for some of the engineering courses. The paper includes several case-studies detailing the student projects in connection to their academic progress. It also suggests the opportunities for our students upon graduation. The key findings of this study are that the research activities enabled by this research initiation grant are sufficiently diverse; they provide necessary supplements for the courses taught to students who specialize in electrical engineering. Research experiences that students get through this project are particularly useful for their future graduate studies and industry careers. 

High levels of carrier injection in polycrystalline Si may arise, for example, in solar cells under concentrated sunlight. Mechanisms for non-radiative carrier recombination include trap-mediated SRH and higher-order processes, e.g., Auger recombination [1]. In this paper we present our experimental results for intensity-dependent carrier lifetimes and conduction currents in polycrystalline Si wafers illuminated with pulses of up to 50 Sun intensity. We also use a computational model for carrier transport that includes both SRH and Auger recombination mechanisms, in order to explain our experiments. The model allows quantifying recombination rate dependence on carrier concentration. Our goal is to relate the recombination rates to Si microstructure and defect densities [2] that are revealed by IR PL images. We acknowledge the NSF support through grant 1505377. [1] A. Richter, S.W. Glunz, F. Werner, J. Schmidt, and A. Cuevas, Improved quantitative description of Auger recombination in crystalline silicon, Phys. Rev. B 86, 165202 (2012). [2] H. C. Sio, T. Trupke, D. Macdonald, Quantifying carrier recombination at grain boundaries in multicrystalline silicon wafers through photoluminescence imaging. J. Appl. Phys. 116, 244905 (2014). 

In this paper we discuss our experimental data obtained for several Si PV cell samples. From the I-V curves measured under various optical irradiance levels, we extracted the fill factors and the series and shunt resistances of the solar cells. For some of our samples, the solar cell efficiencies decrease even at illuminating power densities less than 1 Sun due to reductions in fill factors. Theoretical analysis suggests the reason for the observed dependences of PV cell circuit parameters on optical injection can be defect-mediated carrier recombination.