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Energies 2016, 9(11), 951; doi:10.3390/en9110951

Optimization of Electrochemically Deposited Highly Doped ZnO Bilayers on Ga-Rich Chalcopyrite Selenide for Cost-Effective Photovoltaic Device Technology

1
National Technical University of Athens, Heroon Polytechniou 9, GR-15780 Athens, Greece
2
Technische Universität Berlin, Institut für Festkörperphysik, Hardenbergstr. 36, DE-10623 Berlin, Germany
3
Helmholtz Zentrum Berlin für Materialien und Energie, Institut für Heterogene Materialsysteme, Hahn-Meitner-Platz 1, DE-14109 Berlin, Germany
*
Author to whom correspondence should be addressed.
Academic Editor: Narottam Das
Received: 30 August 2016 / Revised: 1 November 2016 / Accepted: 1 November 2016 / Published: 15 November 2016
(This article belongs to the Special Issue Nano-Structured Solar Cells)
View Full-Text   |   Download PDF [4025 KB, uploaded 15 November 2016]   |  

Abstract

High quality polycrystalline bilayers of aluminium doped ZnO (Al:ZnO) were successively electrodeposited in the form of columnar structures preferentially oriented along the ( 10 1 ¯ 1 ) crystallographic direction from aqueous solution of zinc nitrate (Zn(NO3)2) at negative electrochemical potential of EC = (−0.8)–(−1.2) V and moderate temperature of 80 °C on gallium rich (30% Ga) chalcopyrite selenide Cu(In,Ga)Se2 (CIGS) with chemically deposited ZnSe buffer (ZnSe/Cu(In,Ga)Se2/Mo/glass). The aluminium doped ZnO layer properties have initially been probed by deposition of Al:ZnO/i-ZnO bilayers directly on Mo/glass substrates. The band-gap energy of the Al:ZnO/i-ZnO reference layers was found to vary from 3.2 to 3.7 eV by varying the AlCl3 solute dopant concentration from 1 to 20 mM. The electrical resistivity of indium-pellet contacted highly doped Al:ZnO sheet of In/Al:ZnO/i-ZnO/Mo/glass reference samples was of the order ρ ~10−5 Ω·cm; the respective carrier concentration of the order 1022 cm−3 is commensurate with that of sputtered Al:ZnO layers. For crystal quality optimization of the bilayers by maintenance of the volatile selenium content of the chalcopyrite, they were subjected to 2-step annealing under successive temperature raise and N2 flux regulation. The hydrostatic compressive strain due to Al3+ incorporation in the ZnO lattice of bilayers processed successively with 5 and 12 mM AlCl3 dopant was εh = −0.046 and the respective stress σh = −20 GPa. The surface reflectivity of maximum 5% over the scanned region of 180–900 nm and the (optical) band gap of Eg = 3.67 eV were indicative of the high optical quality of the electrochemically deposited (ECD) Al:ZnO bilayers. View Full-Text
Keywords: CIGS photovoltaics; oriented Al:ZnO bilayers; ECD process optimization; annealing T-threshold; X-ray diffraction; scanning electron microscopy; transmittance/reflectance spectroscopy; current-voltage measurements; van der Pauw measurement techniques CIGS photovoltaics; oriented Al:ZnO bilayers; ECD process optimization; annealing T-threshold; X-ray diffraction; scanning electron microscopy; transmittance/reflectance spectroscopy; current-voltage measurements; van der Pauw measurement techniques
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MDPI and ACS Style

Papadimitriou, D.N.; Roupakas, G.; Roumeliotis, G.G.; Vogt, P.; Köhler, T. Optimization of Electrochemically Deposited Highly Doped ZnO Bilayers on Ga-Rich Chalcopyrite Selenide for Cost-Effective Photovoltaic Device Technology. Energies 2016, 9, 951.

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