Ge incorporation in kesterite thin films by solution processing route: An in-depth study of structural and optoelectronic properties

• Published in: Journal of alloys and compounds Vol. 921; p. 166184
• Main Authors: Mora-Herrera, D., Shaji, S., Pal, Mou
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15-11-2022; Elsevier BV
• Subjects: Antisite defects; Band gap tuning; Chemical composition; Copper zinc tin sulfide; Cu2ZnSn1-xGexS4 thin films; Electronic energy levels; Electronic properties; Energy gap; Germanium; Molecular ink; Optical properties; Optoelectronics; Oxidation; Photoelectrons; Photovoltaic cells; Raman spectra; Solar cells; Solution processing; Spectrum analysis; Thin films; Tin; Valence band; X ray photoelectron spectroscopy; Electronic energy levels; Molecular ink; Band gap tuning; Solution processing; Cu2ZnSn1-xGexS4 thin films
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.166184

Herein, we report a promising solution-processing method for the controlled incorporation of germanium (Ge) into Cu2ZnSnS4 (CZTS) films using a nontoxic molecular ink. The effect of Ge concentration on structural, optical, electrical and electronic properties of the films were systematically investigated. The successful Ge alloying in CZTS was confirmed by XRD analysis and exploring the sensitivity of Raman scattering. The as-synthesized Cu2ZnSn1-xGexS4 (CZTGS; x = 0, 0.1, 0.15, 0.2 and 0.25) films exhibit strong absorption in the visible region with the gradual increment in the band gap energy from 1.46 to 1.61 eV by increasing x from 0 to 0.25. A decrease in Urbach energy at higher [Ge]/[Sn + Ge] ratio supports the reduction of overall disorder into the system. The information about the correct oxidation states of the constituent elements and optimal chemical composition of the CZTGS films was obtained from X-ray photoelectron spectroscopy (XPS). The decrease in SnII/SnIV signal ratio with the increase in Ge further supports the suppression of deep-trap SnZn antisite defects. The XPS valence band spectra reveal that the position of valence band maximum ascended from 0.09 to 0.15 eV with increasing Ge content in the films. Several relevant optical constants were determined of the CZTGS films which are important for applications in solar cell devices as well as for simulation purpose.
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•Highly stable Cu2ZnSn1−xGexS4 (0 ≤ x ≤ 0.25) thin films were obtained by molecular ink approach.•Ge incorporation in kesterite lattice reduces the Urbach energy.•Dielectric loss in kesterite films is decreased by increasing Ge/Sn ratio.•XPS valence band spectra reveals the ascendance of valence band maximum with Ge.