8 October 2014 Sub-bandgap laser annealing of room temperature deposited polycrystalline CdTe
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We investigate how post-deposition laser annealing can be used to improve structural and electronic quality of room-temperature deposited CdTe. We use continuous-wave, 1064 nm laser light to anneal CdTe solar cell stacks prior to back contact deposition. Sub-bandgap optical absorption measurements by photothermal deflection spectroscopy show a reduction of sub-bandgap defects due to the annealing process. Since the 1064 nm light is only partially absorbed, in situ monitoring of the transmitted light during laser annealing gives real-time information about changes in the material. These results reveal an evolution of electronic defect annealing and surface roughness modification with laser exposure time. This hypothesis is supported by electron microscopy. Two distinct annealing regimes emerge: one at low laser power where electronic defect annealing saturates after about one minute exposure and another at high power where structural defects are annealed after several minutes exposure. Temperatures reached during laser annealing are estimated by finite element modeling of the thermal transport due to heat generation from optical absorption.
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Brian J. Simonds, Brian J. Simonds, Sudhajit Misra, Sudhajit Misra, Naba Paudel, Naba Paudel, Koen Vandewal, Koen Vandewal, Alberto Salleo, Alberto Salleo, Christos Ferekides, Christos Ferekides, Michael A. Scarpulla, Michael A. Scarpulla, "Sub-bandgap laser annealing of room temperature deposited polycrystalline CdTe", Proc. SPIE 9180, Laser Processing and Fabrication for Solar, Displays, and Optoelectronic Devices III, 91800F (8 October 2014); doi: 10.1117/12.2062178; https://doi.org/10.1117/12.2062178

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