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Dive into the research topics where João Malaquias is active.

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Featured researches published by João Malaquias.


Applied Physics Letters | 2012

Admittance spectroscopy of Cu2ZnSnS4 based thin film solar cells

P. A. Fernandes; A. F Sartori; P.M.P. Salomé; João Malaquias; A.F. da Cunha; M. P. F Graca; J. C. González

In this report, we propose an AC response equivalent circuit model to describe the admittance measurements of Cu2ZnSnS4 thin film solar cell grown by sulphurization of stacked metallic precursors. This circuit describes the contact resistances, the back contact, and the heterojunction with two trap levels. The study of the back contact resistance allowed the estimation of a back contact barrier of 246 meV. The analysis of the trap series with varying temperature revealed defect activation energies of 45 meV and 113 meV. The solar cell’s electrical parameters were obtained from the J-V curve: conversion efficiency, 1.21%; fill factor, 50%; open circuit voltage, 360 mV; and short circuit current density, 6.8 mA/cm2.


Journal of Physics D | 2010

Mo bilayer for thin film photovoltaics revisited

P.M.P. Salomé; João Malaquias; P. A. Fernandes; A.F. da Cunha

Thin film solar cells based on Cu(In,Ga)Se2 as an absorber layer use Mo as the back contact. This metal is widely used in research and in industry but despite this, there are only a few published studies on the properties of Mo. Properties such as low resistivity and good adhesion to soda lime glass are hard to obtain at the same time. These properties are dependent on the deposition conditions and are associated with the overall stress state of the film. In this report, a study of the deposition of a Mo bilayer is carried out by analysing first single and then bilayers. The best properties of the bilayer were achieved when the bottom layer was deposited at 10 ? 10?3?mbar with a thickness of 500?nm and the top layer deposited at 1 ? 10?3?mbar with a thickness of 300?nm. The films deposited under these conditions showed good adhesion and a sheet resistivity lower than 0.8??.


Scientific Reports | 2017

Deliberate and Accidental Gas-Phase Alkali Doping of Chalcogenide Semiconductors: Cu(In,Ga)Se2

Diego Colombara; Ulrich Berner; A. Ciccioli; João Malaquias; Tobias Bertram; Alexandre Crossay; Michael Schöneich; Helen Meadows; David Regesch; Simona Delsante; G. Gigli; Nathalie Valle; J. Guillot; Brahime El Adib; Patrick Grysan; Phillip J. Dale

Alkali metal doping is essential to achieve highly efficient energy conversion in Cu(In,Ga)Se2 (CIGSe) solar cells. Doping is normally achieved through solid state reactions, but recent observations of gas-phase alkali transport in the kesterite sulfide (Cu2ZnSnS4) system (re)open the way to a novel gas-phase doping strategy. However, the current understanding of gas-phase alkali transport is very limited. This work (i) shows that CIGSe device efficiency can be improved from 2% to 8% by gas-phase sodium incorporation alone, (ii) identifies the most likely routes for gas-phase alkali transport based on mass spectrometric studies, (iii) provides thermochemical computations to rationalize the observations and (iv) critically discusses the subject literature with the aim to better understand the chemical basis of the phenomenon. These results suggest that accidental alkali metal doping occurs all the time, that a controlled vapor pressure of alkali metal could be applied during growth to dope the semiconductor, and that it may have to be accounted for during the currently used solid state doping routes. It is concluded that alkali gas-phase transport occurs through a plurality of routes and cannot be attributed to one single source.


Solar Energy Materials and Solar Cells | 2012

Growth and characterization of Cu2ZnSn(S,Se)4 thin films for solar cells

P.M.P. Salomé; João Malaquias; P. A. Fernandes; M. S Ferreira; A.F. da Cunha; J. P. Leitão; J. C. González; F. M. Matinaga


Solar Energy Materials and Solar Cells | 2013

Effects of sulphurization time on Cu2ZnSnS4 absorbers and thin films solar cells obtained from metallic precursors

P. A. Fernandes; P.M.P. Salomé; A. F Sartori; João Malaquias; A.F. da Cunha; Bjoern-Arvid Schubert; J. C. González; G.M. Ribeiro


Solar Energy Materials and Solar Cells | 2010

Growth pressure dependence of Cu2ZnSnSe4 properties

P.M.P. Salomé; P. A. Fernandes; A.F. da Cunha; J. P. Leitão; João Malaquias; A Weber; J. C. González; M.I.N. da Silva


Thin Solid Films | 2011

Assessment of the potential of tin sulphide thin films prepared by sulphurization of metallic precursors as cell absorbers

João Malaquias; P. A. Fernandes; P.M.P. Salomé; A.F. da Cunha


Advanced Energy Materials | 2014

Cu-rich precursors improve kesterite solar cells

Marina Mousel; Torsten Schwarz; Rabie Djemour; Thomas Paul Weiss; Jan Sendler; João Malaquias; Alex Redinger; Oana Cojocaru-Mirédin; Pyuck-Pa Choi; Susanne Siebentritt


Solar Energy Materials and Solar Cells | 2011

The influence of hydrogen in the incorporation of Zn during the growth of Cu2ZnSnS4 thin films

P.M.P. Salomé; João Malaquias; P. A. Fernandes; M. S Ferreira; J. P. Leitão; A.F. da Cunha; J. C. González; F. N Matinaga; G.M. Ribeiro; Emilson R. Viana


Electrochimica Acta | 2013

Electrodeposition of Cu–In alloys from a choline chloride based deep eutectic solvent for photovoltaic applications

João Malaquias; Marc Steichen; Matthieu Thomassey; Phillip J. Dale

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Marc Steichen

University of Luxembourg

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J. C. González

Universidade Federal de Minas Gerais

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David Regesch

University of Luxembourg

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Helen Meadows

University of Luxembourg

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Jan Sendler

University of Luxembourg

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