Role of hexamethylenetetramine/zinc nitrate hexahydrate molar ratio in controlling structural, morphological and optical properties of ZnO thin films synthesized by CBD

Alphonse Déssoudji Gboglo; Mazabalo Baneto; Ognanmi Ako; Muthiah Haris; Muthusamy Senthilkuma; Alphonse Déssoudji Gboglo; Mazabalo Baneto; Ognanmi Ako; Muthiah Haris; Muthusamy Senthilkuma

doi:10.3934/matersci.2025039

AIMS Materials Science

2025, Volume 12, Issue 4: 893-908. doi: 10.3934/matersci.2025039

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Research article

Role of hexamethylenetetramine/zinc nitrate hexahydrate molar ratio in controlling structural, morphological and optical properties of ZnO thin films synthesized by CBD

1.
Centre d'Excellence Régional pour la Maîtrise de l'Electricité (CERME), University of Lomé, 01BP 1515, Lomé, Togo
2.
Laboratory on Solar Energy, Department of Physics, Faculty of Sciences, University of Lomé, 01BP 1515, Lomé, Togo
3.
School of Arts and Natural Sciences, Joy University, Raja Nagar, Vadakangulam, Near Kanyakumari, Tirunelveli Dist.-627116, Tamil Nadu, India

Received: 11 June 2025 Revised: 31 July 2025 Accepted: 18 August 2025 Published: 05 September 2025

The present study examines the role of the hexamethylenetetramine (HMTA)-to-zinc nitrate hexahydrate (ZNH) molar ratio in controlling the physical properties of zinc oxide (ZnO) thin films obtained by chemical bath deposition (CBD) for potential applications in dye-sensitized solar cells (DSSCs). ZnO thin films were synthesized on glass substrates using aqueous solutions with different HMTA-to-ZNH molar ratios of 0, 1, 2, 3, 4, 5, and 6. The results show that this parameter strongly influences the crystallinity, morphology, and optical characteristics of the films. The X-ray diffraction analysis shows that all the ZnO thin films synthesized are polycrystalline and crystallize in a hexagonal wurtzite structure, with a fluctuating variation in crystallite size (9.5 to 43.7 nm), indicating crystal growth modulated by HMTA. The presence of characteristic functional groups and chemical bonds in ZnO thin films was confirmed by Fourier transform infrared spectroscopy. Scanning electron microscope images revealed that the molar ratio of HMTA/ZNH in the bath solution affected the morphology of the films through grain shape. The films became more compact as molar ratio increased, showing the presence of agglomerated nanotubes. UV-visible analysis showed that films obtained with HMTA/ZNH molar ratio of 4 exhibited the highest transmittance (85%) while those elaborated without HMTA exhibited the lowest transmittance (60%) indicating the impact of HMTA on physical properties of ZnO thin films. Based on structural, morphological, and optical properties, ZnO thin films obtained with HMTA/ZNH molar ratio of 4 are more suitable to be used as a compact electron transport layer in DSSCs to limit charges recombination.
- zinc oxide,
- thin films,
- hexamethylenetetramine,
- zinc nitrate hexahydrate,
- molar ratio,
- chemical bath deposition
Citation: Alphonse Déssoudji Gboglo, Mazabalo Baneto, Ognanmi Ako, Muthiah Haris, Muthusamy Senthilkuma. Role of hexamethylenetetramine/zinc nitrate hexahydrate molar ratio in controlling structural, morphological and optical properties of ZnO thin films synthesized by CBD[J]. AIMS Materials Science, 2025, 12(4): 893-908. doi: 10.3934/matersci.2025039

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Abstract

The present study examines the role of the hexamethylenetetramine (HMTA)-to-zinc nitrate hexahydrate (ZNH) molar ratio in controlling the physical properties of zinc oxide (ZnO) thin films obtained by chemical bath deposition (CBD) for potential applications in dye-sensitized solar cells (DSSCs). ZnO thin films were synthesized on glass substrates using aqueous solutions with different HMTA-to-ZNH molar ratios of 0, 1, 2, 3, 4, 5, and 6. The results show that this parameter strongly influences the crystallinity, morphology, and optical characteristics of the films. The X-ray diffraction analysis shows that all the ZnO thin films synthesized are polycrystalline and crystallize in a hexagonal wurtzite structure, with a fluctuating variation in crystallite size (9.5 to 43.7 nm), indicating crystal growth modulated by HMTA. The presence of characteristic functional groups and chemical bonds in ZnO thin films was confirmed by Fourier transform infrared spectroscopy. Scanning electron microscope images revealed that the molar ratio of HMTA/ZNH in the bath solution affected the morphology of the films through grain shape. The films became more compact as molar ratio increased, showing the presence of agglomerated nanotubes. UV-visible analysis showed that films obtained with HMTA/ZNH molar ratio of 4 exhibited the highest transmittance (85%) while those elaborated without HMTA exhibited the lowest transmittance (60%) indicating the impact of HMTA on physical properties of ZnO thin films. Based on structural, morphological, and optical properties, ZnO thin films obtained with HMTA/ZNH molar ratio of 4 are more suitable to be used as a compact electron transport layer in DSSCs to limit charges recombination.

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