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13. Structure and optical properties of La-doped ZnO thin films at room temperature

Author

Sugihartono Iwan, Soegijono Bambang, Handoko Erfan, Tiam Tan Swee, and Umar Akrajas Ali

Subjects
la-doped zno, thin films, ultrasonic spray pyrolysis, structure, photoluminescence, Clay industries. Ceramics. Glass, TP785-869
Abstract

La-doped ZnO (with 0, 1, 5 and 7 wt.% La) thin films were deposited on Si substrates by ultrasonic spray pyrolysis, using frequency of 1.7MHz, and heated at 450°C for 15min. The effect of La addition on the structural and optical properties of ZnO thin films was analysed. X-ray diffraction patterns confirmed that all prepared thin films had a polycrystalline hexagonal wurtzite structure with highly preferred texture in the (002) plane in the case of the ZnO containing 7 wt.% La. Atomic force microscopy analyses confirmed that the surface morphology is affected by La addition and the root mean square (RMS) roughness tended to be higher by increasing La content. The optical band gap energies of the La-doped thin films are smaller than that of the undoped ZnO. The photoluminescence properties of the prepared thin films confirmed that there was a significant redshift of DLE to wavelength of 711 nm when 1wt.% of La was incorporated in ZnO structure. It was proposed that the incorporation of La into the ZnO structure caused the oxygen atoms to have a strong bond with La.

Published
2023
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29. Enhancing the Phase Crystallinity of Buried Layer Perovskites through Organic Salt Molecule‐Assisted Crystal Growth.

Author

Umar, Akrajas Ali, Devkota, Nim Bahadur, Dai, Shijie, Ahmed, Waqar, Li, Xiaoguo, Wang, Jiao, Yu, Anran, and Zhan, Yiqiang

Subjects
SOLAR cells, CRYSTAL growth, SURFACE structure, SALT crystals, METHENAMINE
Abstract

The performance and stability of perovskite solar cells rely crucially on the purity of their active perovskite phase. While the two‐step method has emerged as a well‐known technique for fabricating high‐performance cells, it suffers from significant PbI2 phase impurities at the buried layer due to inefficient diffusion of cationic molecules into the preprepared PbI2 layer. Herein, a simple yet highly effective method is presented to boost phase purity within the buried layer by introducing formamidinium iodide (FAI) seed molecules into the underlying PbI2 layer. X‐Ray diffraction analysis result reveals that this process significantly reduces the PbI2 phase and enhances the purity of the perovskite's phase. It is also observed that this technique can produce perovskite layer with a remarkably smooth surface structure and large interconnected crystal grains, forming a continuous layer. These characteristics are subjected to further enhancement when hexamethylenetetramine molecules are concurrently introduced with FAI into the PbI2 layer. Solar cells fabricated using this method, with an active area of 0.1 cm2, achieve a remarkable power conversion efficiency of up to 24.52% with Voc as high as 1.18 V, representing a substantial improvement over cells produced using the standard two‐step method, which attains only 22.18% efficiency. With its simple yet impactful approach, the present method should find widespread adoption in the production of high‐performance perovskite solar cells. [ABSTRACT FROM AUTHOR]

Published
2024
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30. Enhancing cyclic voltammetry performance with N-graphene -supported coupled NiO/TiO2 hollow nanospheres as superior anode material.

Author

Azis, Thamrin, Ashari, Lintan, Muzakkar, Muhammad Zakir, Nurdin, Muhammad, Mulkiyan, La Ode Muhammad Zuhdi, Salim, La Ode Agus, Edihar, Muh, and Umar, Akrajas Ali

Abstract

In this work, we aim to study and improve the electrochemical performance of a unique thin film-structured composite nitrogen-doped graphene (NGr) combined with NiO/TiO2 hollow nanospheres coupled by synergistic hydrothermal method. NGr@NiO/TiO2 nanocomposites have been successfully synthesized as indicated by their characteristics through several rational characterization techniques such as the morphological shape of NiO/TiO2 hollow nanospheres that are evenly distributed on the surface of N-graphene with particle distribution in the range of 79.78–362.13 nm with an average diameter of 130 nm. In addition, the crystal structures of carbon from NGr, NiO, and TiO2 (anatase and rutile) have been confirmed and proven by spectra showing the presence of C–N stretching primary amides (1400 cm−1), Ni–O stretching (700 cm−1) and Ti–O–Ti bond (425 cm−1), respectively. To enhance the performance of cyclic voltammetry (CV) in electrochemical testing, adjustments are made to parameters such as cycle effect, scan rate, and composition, ensuring the production of reversible voltammograms under each condition. The results indicate that reversible voltammograms are observed under each condition, with a composite ratio of 80:15:5 (wt%). Slower scan rates are associated with higher specific capacity (Cps), with the Cps values for the NGr@NiO/TiO2 electrode being 741.02 F/g (80:10:10), 408.53 F/g (80:5:10), and 839.83 F/g (80:15:5), respectively. However, the highest Cps is recorded for NGr@NiO at 1959.71 F/g. Based on these findings, it is revealed that further comprehensive electrochemical testing of the NGr@NiO/TiO2 nanocomposite is necessary, to fully explore its potential and applicability in the development of alkaline ion batteries (AIBs) such as Li/Na/K. [ABSTRACT FROM AUTHOR]

Published
2024
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