Abstract-Thin Film Polycrystalline Silicon Solar Cells Studied by Transient Terahertz Probe Spectroscopy

• Peter Pikna^a, 
• Volodymyr Skoromets^b, 
• Christiane Becker^c, 
• Antonín Fejfar^a, 
• Petr Kužel^b, 

• ^a Institute of Physics ASCR, Cukrovarnická 10, 16253 Prague 6, Czech Republic
• ^b Institute of Physics ASCR, Na Slovance 2, 18221 Prague 8, Czech Republic
• ^c Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Kekuléstraße 5, 12489 Berlin, German

http://www.sciencedirect.com/science/article/pii/S1876610216315387
Thin film polycrystalline silicon (poly-Si) solar cells were annealed in hydrogen plasma or in water vapour to suppress electrical activity of defects and impurities (passivation). The hydrogen plasma passivation procedure was optimized and a modification of several hydrogenation parameters was suggested, e.g. higher hydrogen pressure of 300 Pa and keeping bias voltage V_bias constant during the whole passivation process until the plasma was switched off. Since the plasma hydrogenation process was run as a closed system (without hydrogen flow) and the achieved passivation results (up to 497 mV) were close to the limit for poly-Si (500 mV), the generally accepted necessity to operate the process with a hydrogen flow was called into question. Samples passivated in a hydrogen plasma at different processing conditions were analyzed by transient terahertz probe spectroscopy and Suns-V_OC method to measure a solar cell's charge carrier lifetime and its open-circuit voltage V_OC, respectively. A correlation of these measured parameters was observed even though both these techniques characterize solar cells in completely different states. The transient terahertz probe spectroscopy appears to be a useful tool for a contactless investigation of materials where ultrafast processes of ns-long lifetimes play a crucial role, e.g. nanostructured objects and materials.

Abstract-Conductivity Mechanisms in Sb-doped SnO2 Nanoparticle Assemblies: Dc and Terahertz Regime

Volodymyr Skoromets , Hynek Němec , Jaromír Kopeček , Petr Kuzel , Kristina Peters , Dina Fattakhova-Rohlfing , Aliaksei Vetushka , Martin Müller , Kristína Ganzerová , and Antonin Fejfar

J. Phys. Chem. C, Just Accepted Manuscript

DOI: 10.1021/acs.jpcc.5b05091

Publication Date (Web): July 27, 2015

Copyright © 2015 American Chemical Societ

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.5b05091

Assemblies of undoped and antimony-doped tin-oxide nanoparticles synthesized via non-aqueous sol-gel procedure, pressed into pellets, and annealed under various conditions were investigated using time-domain terahertz spectroscopy, scanning electron microscopy, atomic force microscopy and dc conductivity measurements. Combination of these methods made it possible to resolve the conductivity limitations imposed by intrinsic properties of the material and by the morphology of the samples. Percolation of the nanoparticles was confirmed in all samples. The undoped samples exhibit a weak hopping conductivity, whereas band-like conduction of charges partially confined in the nanoparticles dominates in the doped samples. The conductivity of nanoparticles and their connectivity can be greatly controlled during the sample preparation, namely by the calcination temperature and by the order of technological steps. Substantial increase of the conductivity inside nanoparticles and of the charge transport between them is achieved upon calcination at 500°C.

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