On the formation mechanisms of Zn-rich Cu2ZnSnS4 films prepared by sulfurization of metallic stacks

The future development of Cu2ZnSnS4 (CZTS) as an alternative absorber for low cost and high efficiency thin film photovoltaic modules depends strongly on the understanding and control of the formation of secondary phases in this system. With this aim, a detailed chemical-physical characterization of...

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Bibliographic Details
Published in:Solar energy materials and solar cells 2013-05, Vol.112, p.97-105
Main Authors: Fairbrother, Andrew, Fontané, Xavier, Izquierdo-Roca, Victor, Espíndola-Rodríguez, Moises, López-Marino, Simon, Placidi, Marcel, Calvo-Barrio, Lorenzo, Pérez-Rodríguez, Alejandro, Saucedo, Edgardo
Format: Article
Language:English
Subjects:
Annealing
Applied sciences
Auger spectroscopy
CZT
CZTS
Direct energy conversion and energy accumulation
Electrical engineering. Electrical power engineering
Electrical power engineering
Energy
Equipments, installations and applications
Exact sciences and technology
Formation mechanism
Kesterite
Natural energy
Phase formation
Phases
Photoelectric conversion
Photovoltaic cells
Photovoltaic conversion
Raman spectroscopy
Solar cells
Solar cells. Photoelectrochemical cells
Solar energy
Stacks
Sulfurization
Zinc
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Summary:The future development of Cu2ZnSnS4 (CZTS) as an alternative absorber for low cost and high efficiency thin film photovoltaic modules depends strongly on the understanding and control of the formation of secondary phases in this system. With this aim, a detailed chemical-physical characterization of Zn-rich CZTS films prepared by sulfurization of metallic stacks is presented, combining x-ray diffraction, Raman, and Auger spectroscopy. Under such conditions a reaction pathway for the formation of CZTS by a solid–liquid–gas reaction with binary compounds as intermediates is proposed. This is supported by the detailed depth-resolved analysis of the films annealed at different temperatures and times. The experimental data support a formation mechanism of CZTS that proceeds rapidly when a eutectic Cu2S+SnS mixture melts above 480°C, acting as a flux to react the remaining solid binary phases and sulfur gas present in the annealing atmosphere. During reaction Cu and Sn are completely consumed, while excess Zn segregates towards the back contact regions as shown by a combined Raman–Auger depth-resolved analysis. Using the presented thermal treatment process a device with 5.5% efficiency and a maximum external quantum efficiency of 79% is obtained. [Display omitted] ► Chemical-physical depth-resolved analysis on the formation mechanisms of Cu2ZnSnS4. ► Evidence of a Cu2S+SnS eutectic mixture being critical for Cu2ZnSnS4 formation. ► Proposed reaction via a solid–liquid–gas reaction of binary compounds and sulfur. ► Preparation of a 5.5% efficiency photovoltaic device with sulfur-pure Cu2ZnSnS4.
ISSN:0927-0248
1879-3398
DOI:10.1016/j.solmat.2013.01.015