| Autor: |
Yoon Y; Physical Measurement Laboratory , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States.; Maryland NanoCenter , University of Maryland , College Park , Maryland 20742 , United States., Yang WD; Physical Measurement Laboratory , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States.; Maryland NanoCenter , University of Maryland , College Park , Maryland 20742 , United States., Ha D; Physical Measurement Laboratory , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States.; Maryland NanoCenter , University of Maryland , College Park , Maryland 20742 , United States., Haney PM; Physical Measurement Laboratory , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States., Hirsch D; Fraunhofer Institute for Organic Electronics , Electron Beam and Plasma Technology FEP , Winterbergstrasse 28 , 01277 Dresden , Germany., Yoon HP; Department of Electrical and Computer Engineering , University of Utah , Salt Lake City , Utah 84112 , United States., Sharma R; Physical Measurement Laboratory , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States., Zhitenev NB; Physical Measurement Laboratory , National Institute of Standards and Technology , Gaithersburg , Maryland 20899 , United States. |
| Abstrakt: |
Solar cells made of polycrystalline thin-films can outperform their single-crystalline counterparts despite the presence of grain boundaries (GBs). To unveil the influence of GBs, high spatial resolution characterization techniques are needed to measure local properties in their vicinity. However, results obtained using single technique may provide limited aspects about the GB effect. Here, we employ two techniques, near-field scanning photocurrent microscopy (NSPM) and scanning transmission electron microscope based cathodoluminescence spectroscopy (STEM-CL), to characterize CdTe solar cells at the nanoscale. The signal contrast from the grain interiors (GIs) to the GBs, for high-efficiency cells where CdTe is deposited at a high substrate temperature (500 °C) and treated by CdCl 2 , is found reverse from one technique to another. NSPM reveals increased photocurrents at the GBs, while STEM-CL shows reduced CL intensity and energy redshifts of the spectral peak at the GBs. The results are attributed to the increased nonradiative recombination and the band bending mediated by the surface defects and the shallow-level defects at GBs, respectively. We discuss the advantages of sample geometry for room-temperature STEM-CL and present numerical simulations as well as analytical models to extract the ratio of GB recombination velocity to minority carrier diffusivity that can be used for evaluating the GB effect in other polycrystalline solar cells. |
