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Communication Dans Un Congrès Année : 2024

ZnMgO by ultrasonic spray pyrolysis as a buffer layer in sustainable thin-film solar cells: study of the temperature dependence of electrical transport properties

Résumé

Recently ZnMgO demonstrated a crucial interest in thin-film solar cells as buffer layers to replace toxic and nonabundant elements such as cadmium (crustal abundance (CA): 0.25 ppm) or indium (CA: 0.15 ppm). Indeed, (i) it contains only abundant and nontoxic elements (Zn, CA: 70 ppm, Mg, CA: 23300 ppm); (ii) can be synthesized using energy efficient, low cost and industry scalable techniques such as ultrasonic spray pyrolysis; (iii) its properties can be widely modulated by changing the Mg composition. In this work, ZnMgO thin films were deposited and optimized using a two-step process based on ultrasonic spray pyrolysis technique and thermal post annealing. In these films, the understanding and control of the electrical properties are of crucial importance to be integrated as buffer layer in thin-film solar cells where the band alignment, the carrier concentration and density of defects are the main keys to optimize the heterointerface with the absorber. The underlying mechanisms are not yet fully investigated and we propose here a comprehensive study of these electrical properties with respect to measurement temperature (40 K to 340 K), annealing temperature (520 K to 770 K) and Mg composition (0 % to 5 %). The optimization of ohmic contacts on ZnMgO was conducted using aluminum and that of Schottky contacts was performed using gold with the thermal evaporation technique. The transport properties were measured using van der Pauw technique and I-V-T (current-voltage with respect to temperature). We have developed a model to analyze the transport properties with respect to the temperature and magnesium composition by considering the ionized impurity and phonon scattering as new approach to investigate the shallow donors’ properties in ZnMgO. In particular, this combined experimental/theoretical approach gives a way to explain the origin of the resistivity variation with the temperature as related to a decrease in the concentration of shallow donors, an increase in their activation energy and the presence of a compensating deep defects in ZnMgO. The electrical results were correlated to the optical transmission in particular to analyze the variation of bandgap and Urbach energy correlated to the transport properties variation. Indeed, the resistivity trend, in the 0.01 Ohm.cm – 10 Ohm.cm range, is well correlated to the variation of the bandgap with Mg composition which increases from 3.28 eV to 3.36 eV and Urbach energy varying in the 0.060 eV – 0.100 eV range. This comprehensive investigation of the electrical properties gives better understanding of the complex mechanisms involved in these films and thus permit to optimize their use in sustainable solar cells as buffer layers.
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Dates et versions

hal-04625062 , version 1 (25-06-2024)

Identifiants

  • HAL Id : hal-04625062 , version 1

Citer

Victor Colas, Wafae El Berjali, Krishna Lone, Sidi Ould Saad Hamady. ZnMgO by ultrasonic spray pyrolysis as a buffer layer in sustainable thin-film solar cells: study of the temperature dependence of electrical transport properties. European Materials Research Society (E-MRS) Spring Meeting, May 2024, Strasbourg, France. ⟨hal-04625062⟩
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