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    Enhanced photovoltaic performance of silicon-based solar cell through optimization of Ga-doped ZnO layer
    (Iop Publishing Ltd, 2023) Erkan, Serkan; Altuntepe, Ali; Yazici, Duygu; Olgar, Mehmet Ali; Zan, Recep
    In the present study, the impact of deposition pressure and substrate temperature of Ga-doped Zinc Oxide (GZO) thin film and the photovoltaic performance of this structure as a transparent conductive oxide (TCE) layer in silicon-based solar cell were investigated. Implementing a single target of GZO, the structural, optical, and electrical properties of 350 nm thick GZO thin films with various deposition pressure (5 mTorr, 10 mTorr, 15 mTorr and 20 mTorr) at room temperature (RT) and substrate temperature (RT, 150 degrees C, 200 degrees C, 250 degrees C) at 15 mTorr deposition pressure were fabricated using RF magnetron sputtering technique. The aim here was to find out the GZO films with the optimum pressure and substrate temperature to incorporate them into solar cell as a TCE layer. The X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques were used to determine the structural properties of all samples. The optical transmission measurements were performed using spectroscopic Ellipsometer and the band gap values were calculated by Tauc plot using optical transmission data. In addition, the electrical characterization of the GZO samples were analyzed by the Van der Pauw method and Hall measurements. Finally, the most promising GZO thin film was determined based on the structural and optoelectrical characterization. The findings indicated that the XRD pattern of all the prepared films was dominated by (002) preferential orientation irrespective of the deposition pressure and substrate temperature. The AFM measurements showed that all the samples had a dense surface morphology regardless of the deposition pressures, but the surface morphology of the samples was clearly changed upon increasing substrate temperatures. The transmission values of the film did not significantly alter (similar to 82%) when the deposition pressures except for the substrate temperature of 200 degrees C (86%) were changed. The band gap values were calculated between 3.30 eV and 3.36 eV, which can be associated with enhancement of crystalline quality of the films. The lowest resistivity and the highest carrier concentration values belonged to the film fabricated at 15 mTorr@200 degrees C by 2.0 x 10-3 omega.cm and 1.6 x 1020 cm-3, respectively. Both increasing the deposition pressure (up to 15 mTorr) and substrate temperature (up to 200 degrees C) contributes to improving the crystallite size, widening the optical band gap, lowering the resistivity, and increasing the carrier concentration. In order to evaluate and compare the effect of both deposition pressure and substrate temperature, Silicon-based solar cells were fabricated using the most promising layers (15 mTorr@RT, 15 mTorr@200 degrees C). The cell performance with the GZO thin film as a TCE layer showed that varying both the pressure and substrate temperature of the GZO film contributed to enhancing the solar cell parameters. Thus, the conversion efficiency increased from 9.24% to 12.6% with the sequential optimization of pressure and temperature. It can be concluded that the pressure applied during the deposition and substrate temperature had a significant impact on the properties of GZO thin films and its photovoltaic performance of solar cell used as TCE layer.
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    Performance of Si-based solar cell utilizing optimized Al-doped ZnO films as TCO layer
    (Springer, 2023) Altuntepe, Ali; Erkan, Serkan; Hasret, Onur; Yagmyrov, Atajan; Yazici, Duygu; Tomakin, Murat; Olgar, Mehmet Ali
    Aluminum-doped zinc oxide (AZO) is one of the most popular transparent conducting oxide layers that can be employed in many optoelectronic applications in particular in photovoltaic devices due to being a low-cost and nontoxic material. In this study, we report on the effect of deposition pressure and substrate temperature on the properties of AZO films and solar cell performance by employing the optimized films. This study consists of two stages, the first of which concerns the optimization deposition pressure while the second is the substrate temperature of AZO films by evaluating the structural, optical, and electrical properties of the films. The deposited AZO thin film under 10 mTorr deposition pressure exhibited high optical transmission (89.9%), low electrical resistivity (9.1 x 10(-2) omega.cm), and high carrier concentration (3.74 x 10(19) cm(-3)) among the others. The impact of substrate temperature was then investigated using this deposition pressure at room temperature, 150, 200, and 250 ?. The deposited AZO films at 150 ? temperature were found to possess the highest optical transmission (91.1%), lowest resistivity (9.9 x 10(-4) omega.cm), and highest carrier concentration (1.1 x 10(20) cm(-3)) values. Hence, the 10 mTorr deposition pressure and 150 ? substrate temperature were selected as the optimum growth parameters to obtain AZO films, which were then employed in the cell structure. It was, thus, revealed that utilizing AZO films in silicon-based solar cell using such parameters led to the enhancement in the cell efficiency.