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"Seng oksida (ZnO) merupakan material semikonduktor dengan aplikasi yang sangat luas dalam berbagai bidang seperti elektronik, optoelektronik, fotokatalisis, hingga biomedis. Salah satu aplikasi yang marak diteliti saat ini adalah penggunaan ZnO sebagai lapisan anoda untuk sel surya tersensitasi zat pewarna (dye-sensitized solar cell, DSSC). Dalam pembuatan sel surya, kondisi morfologi natural lapisan semikonduktor oksida sangat berpengaruh pada interaksi penyerapan cahaya. Bentuk morfologi yang baik adalah struktur one-dimensional (1D) yang tersusun secara paralel dan melekat secara vertikal pada substrat kaca konduktif. Akan tetapi, struktur ini tidak mudah didapat pada sintesis dengan metode kimiawi basah. Pertumbuhan nanostruktur dengan arah yang tidak terorientasi akan mengakibatkan rendahnya kristalinitas dan energi celah pita (Eg) yang tinggi. Hal ini dapat menyebabkan rendahnya kemampuan penyerapan zat pewarna (dye) yang memberikan hasil DSSC dengan efisiensi rendah. Pada penelitian ini, dilakukan sintesis nanostruktur ZnO di atas substrat kaca konduktif dengan bahan dasar seng nitrat tetrahidrat (Zn(NO3)2.4H2O, Zn-nitrat) dan heksametilentetraamin (C6H12N4, HMTA). Untuk meningkatkan kestabilan lapisan ZnO di atas substrat, dilakukan penempelan lapisan bibit terlebih dahulu dengan menggunakan metode spin-coating. Lapisan bibit ini dibuat dengan menggunakan larutan yang disintesis pada suhu 0oC. Setelah proses spin-coating, lapisan nanostruktur ZnO ditumbuhkan dengan menggunakan metode chemical bath deposition (CBD). Untuk meningkatkan kristalinitas nanostruktur ZnO, dilakukan proses pasca-hidrotermal, yang terbagi menjadi 2 variasi. Pada variasi pertama, reaksi dilakukan dalam reaktor hidrotermal pada 150oC selama 3 jam. Pada variasi kedua, reaksi dilakukan dalam reaktor tertutup dengan penambahan gas nitrogen (N2) 1 bar pada suhu 100oC selama 1 jam. Hasil penelitian menunjukkan bahwa perlakuan pasca-hidrotermal, menhasilkan lapisan nanostruktur ZnO dengan kristalinitas yang lebih tinggi, ditandai dengan intensitas puncak difraksi yang lebih tajam dibandingkan dengan ZnO hasil as-synthesized. Naiknya kristalinitas tersebut selanjutnya memicu penurunan energi celah pita (Eg) sehingga lapisan nanostruktur ZnO dapat menyerap cahaya pada panjang gelombang yang lebih besar. Selain itu, morfologi yang yang terlihat dari hasil SEM juga menunjukkan perbaikan setelah proses pasca-hidrotermal. Hal ini terlihat orientasi nanostruktur ZnO yang semula tidak beraturan menjadi tegak vertikal. Dalam penelitian ini, diketahui bahwa perbedaan kondisi pasca-hidrotermal menghasilkan pertumbuhan nanostruktur dengan bentuk yang berbeda. Pada variasi pertama, didapat hasil sintesis berupa nanorods ZnO, sedangkan variasi kedua menghasilkan nanorods dan nanotubes ZnO. Nanostruktur ZnO di atas substrat kaca konduktif yang telah dihasilkan selanjutnya digunakan sebagai lapisan anoda pada DSSC. Pada penelitian ini, terlihat bahwa perbedaan variasi proses pasca-hidrotermal mempengaruhi kemampuan penyerapan warna (dye loading). Anoda yang dihasilkan dari proses pasca-hidrotermal yang menggunakan penambahan gas N2 mampu menyerap za pewarna lebih banyak. Hal ini diduga disebabkan oleh adanya struktur nanotubes yang memiliki pori/rongga. Namun demikian, efisiensi tertinggi diraih oleh anoda setelah perlakuan pasca-hidrotermal tanpa gas N2, yaitu sebesar 0,12%. Nilai ini bersesuaian dengan ukuran kristalit yang paling stabil dan energi celah pita paling rendah yang didapat dari perhitungan. Pada penelitian, diameter kristalit dan energi celah pita pada sampel dengan efisiensi tertinggi adalah sebesar ~18 nm dan 3,17 eV.

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Zinc oxide (ZnO) is a semiconductor material with a very broad application in many fields, such as electronics, optoelectronic, photocatalyst, and biomedicine. One application that widely examined nowadays is its use as an anode layer for dye-sensitized solar cells (DSSC). In solar cells fabrication, the nature of morphological conditions of the oxide semiconductor layer greatly affect the interaction of light absorption. Good morphology is a one-dimensional structure (1D) arranged in parallel and attached vertically on a conductive glass substrate. However, this structure is not easily obtained in the synthesis via wet chemical method. Nanostructures with non-oriented growth will result in lower crystallinity and higher band gap energy (Eg) is high. This can lead to low dye absorption that results in DSSC with low efficiency.

In this study, synthesis of ZnO nanostructures on a conductive glass substrate was carried out using zinc nitrate tetrahydrate (Zn(NO3)2.4H2O, Zn-nitrate) and heksametilentetraamin (C6H12N4, HMTA) at 0oC. To improve the stability of ZnO layer on the substrate, seeding layers were attached using spin-coating method. After the spin-coating process, the seeding layers were grown using chemical bath deposition (CBD). To improve the crystallinity of nanostructured ZnO, post-hydrothermal process was performed afterward. This process was divided into two variations. In the first variation, the reaction is carried out in a hydrothermal reactor at 150oC for 3 hours. While in the second variation, the reaction is carried out in a closed reactor with the addition of 1 bar nitrogen gas (N2) at 100° C for 1 hour.

The results showed that post-hydrothermal treatment had improved the ZnO nanostructures layer. The diffraction peaks were sharper than the as-synthesized ZnO nanostructure, indicating higher crystallinity. As a consequence, the band gap energy would be lowered. In addition, the morphology also showed improvement in the nanostructures orientation after a post-hydrothermal process. In this research, the difference in the post-hydrothermal conditions generated different shapes of ZnO nanostructures. The first variation resulted ZnO nanorods, while the second variation produced ZnO nanorods and nanotubes.

In this study, it appeared that post-hydrothermal process variations affected the dye loading capacity of the ZnO nanostructure layers. When used as anodes in DSSC, the layer obtained from post-hydrothermal process using N2 gas additions showed a higher dye absorption. The presence of nanotubes structure was assumed to gave this contribution, since this structure had pores / cavities that could absorbed more dyes. However, the highest efficiency achieved by the anode after post-hydrothermal treatment without N2 gas, with the value of 0.12%. This corresponded with the most stable crystallites size and lowest band gap energy obtained from the calculation. In the study, the crystallites size and the band gap energy of this sample were given as ~ 18 nm and 3.17 eV."

"Zinc oxide (ZnO) nanorods have been considered as a potential semiconductor oxide material for the application of dye-sensitized solar cells (DSSC). Various experiments have been conducted to improve its nanostructural characteristics and functional properties in order to make it well suited for enhancing DSSC’ performance. Inspired by such studies, the ZnO nanorods array was grown on indium tin oxide (InSn2O3, ITO) substrate in the present work. For this purpose, a seed solution was prepared at low temperature (0oC) using zinc nitrate tetrahydrate and hexamethylenetetramine. The ZnO seed layers were deposited onto ITO glass using a spin-coating technique and further annealed at two different temperatures, 200 and 400 oC. The seeding was also varied between one, three and five layers, prior to the growing process using the chemical bath deposition method (CBD). The results showed that the annealing temperatures significantly influenced the ZnO nanorods’ growth. The optimal condition was achieved by using three seed layers annealed at 200oC, providing an average diameter of 157.58 nm, the biggest crystallite size (up to 59.63 nm), and a band-gap energy (Eg) of 3.27 eV. Based on the obtained properties, the growth of ZnO nanorods on ITO substrate in this work has the potential to be used for the application of dye-sensitized solar cells."

"Among semiconductors, zinc oxide (ZnO) has received great attention due to its wide band-gap and high electron mobility, resulting in various strategic applications. Controlling the physical properties of ZnO is therefore a critical issue in the fabrication of related electronic and optical devices. In this study, ZnO nanorods layers were grown on an ITO glass substrate via chemical bath deposition at low temperature. Prior to the growing process, the layers were deposited using a spin-coating technique. The seeding solution was made by dissolving zinc nitrate tetrahydrate and hexamethylene tetraamine in cold water (0oC) for an hour using a cooler bath. The as-synthesized ZnOs were further subjected to different post-hydrothermal treatment series at a temperature of 150oC for three hours at atmospheric pressure and at 100°C for one hour under one bar of nitrogen gas (N2) pressure. The characterization was performed using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and UV-Vis spectroscopy. The SEM results showed that the ZnO nanorods were grown as a vertically aligned hexagonal structure, while the XRD patterns showed a high intensity at the (002) plane. On the basis of investigation, it was found that under post-hydrothermal treatment at 150oC for three hours with atmospheric pressure, the synthesis procedure resulted in nanostructures in the form of ZnO rods. Meanwhile, post-hydrothermal treatment at 100°C for one hour under one bar of nitrogen gas (N2) produced ZnO rods and tubes. In general, the post-hydrothermal process provided a high degree of crystallinity. The optimum ZnO layer was obtained after post-hydrothermal treatment at 150oC for three hours at atmospheric pressure, with a crystallite size and band-gap energy of ~18 nm and 3.20 eV, respectively."