Investigation of recombination mechanisms of CdTe solar cells with different buffer layers

In this study, close-spaced sublimation (CSS) grown cadmium telluride (CdTe) thin films with good adhesion to 100 µm thin Schott D263T ultra-thin glass (UTG) were investigated. Cadmium chloride (CdCl2) treatment in vacuum ambient was executed to enhance the film quality and optoelectrical properties of CdTe thin film. The post-deposition annealing temperature ranging from 360–420 °C was examined to improve the CdTe film quality on UTG substrate. Various characterization techniques have been used to observe the compositional, morphological, optical, as well as electrical properties. Scanning electron microscopy (SEM) verified that the CdTe morphology and grain size could be controlled via CdCl2 treatment temperature. Energy Dispersive X-Ray Analysis (EDX) results confirmed that the annealing temperature range of 375–390 °C yielded the stoichiometric CdTe films. UV-Vis analysis estimated the post-treatment bandgap energy in the range of 1.39–1.46 eV. Carrier concentration and resistivity were obtained in the order of 1013 cm−3 and 104 Ω-cm, respectively. All the experimental results established that the CdCl2 treatment temperature range of 390–405 °C might be considered as the optimum process temperature for the deposition of CdTe solar cell on UTG substrate in close-spaced sublimation (CSS) method.

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“…CdTe thin-film solar cells are a promising choice for terrestrial utilization [1]. CdTe has an optimal direct band gap of 1.5 eV [2].…”

Section: Introductionmentioning

confidence: 99%

Impact of CdCl2 Treatment in CdTe Thin Film Grown on Ultra-Thin Glass Substrate via Close Spaced Sublimation

2021

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“…6 The band structure of semiconductors provide appropriate band alignment which help carriers generated in the window layer and absorber layer be collected, enhancing the quantum efficiency throughout the whole visible wavelength range. This can also explain why the quantum efficiency in the short wavelength region was enhanced though CdSe 1-x S x films have smaller E g than CdS film [15,17].…”

Section: The Electronic Structure Of Cdse 12x S X Filmsmentioning

confidence: 94%

“…Using CdSe window layer can enhance J sc [11][12][13][14] but the open circuit voltage (V OC ) and fill factor (FF) decrease [11,12]. The work of ours and others shows that using CdS/CdSe composite window layer can enhance J sc and maintain V OC and thus improve the device efficiency [15][16][17][18][19]. To find out the reasons for this, some work has been done.…”

Section: Introductionmentioning

confidence: 90%

“…Our previous work shows that CdSe films can act as a protective layer to avoid the excessive CdS consumption during the high-temperature device preparation process, guaranteeing good pn junction [15]. The buffer/absorber interface can be modified and interface recombination is reduced using CdS/CdSe composite window layer [17]. However, the mechanism of the high quantum efficiency in the short wavelength region remains unknown.…”

Section: Introductionmentioning

confidence: 99%

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Properties of CdSe1−xSx films by magnetron sputtering and their role in CdTe solar cells

Wang

et al. 2020

J Mater Sci: Mater Electron

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CdS/CdSe composite window layer is a better candidate than CdS or CdSe single layer for CdTe solar cells. In order to find the underlying reason, the properties of co-sputtered CdSe 1-x S x thin films with different compositions (0 x 1) were examined. XRD patterns show that all CdSe 1-x S x films (0 x 1) are polycrystalline with hexagonal structures and the prominent peak position shows an increasing trend with the increase of x. This suggests that CdSe 1-x S x window layer with a gradient composition, formed during the hightemperature growth and heat treatment of CdTe films, has the gradient lattice constant, meaning the less defect density. This is beneficial to the device performance. Hall measurements show that CdS 1-x Se x films (x C 0.772) are n-type semiconductors with carrier concentrations ranging from 10 15 cm -3 to 10 16 cm -3 . It reveals that CdS/CdSe bi-layers can form a strong built-in electric field with CdTe layer as CdS does. The electronic band structure of CdSe 1-x S x window layer with a gradient composition suggests that the spikes formed in the conduction band are lower than 0.3 eV, which would not impede the electron transport. The valence band alignment is beneficial for the hole transport. Therefore, an appropriate band alignment can be formed between CdSe 1-x S x and CdTe layers. These results reveal that CdSe 1-x S x film is a good candidate as the window layer for high-efficiency CdTe solar cells considering its structural, optical and electrical properties as well as its electronic structure.

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“…The Voc is the maximum possible voltage from a solar cell. An expression for Voc [46] is presented by setting the J=0 in the Eq. ( 3)…”

Section: Numerical Modelingmentioning

confidence: 99%

Thin oxide buffer layers for avoiding leaks in CIGS solar cells; a theoretical analysis

Ghamsari-Yazdel

Gharibshahian

Sharbati

2021

J Mater Sci: Mater Electron

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The purpose of this research is the performance improvement of the CIGS/CdS/ZnO solar cells, while the CdS buffer layer is too thin. Enhancement of photocurrent by decreasing the thickness of CdS buffer layer is expected from a reduced parasitic absorption at short wavelengths. However, the formation of pinholes due to the too-thin CdS buffer layer and a non-uniform coverage of the CIGS surface degrades the solar cell performance by reducing fill factor (FF) and open-circuit voltage (Voc). This degradation is because the direct contact of ZnO and CIGS could exist in pinholes, and the formation of the cliff-like band alignment at CIGS/ZnO interface increases the recombination rate. In this work, to eliminate this destructive effect in the CIGS solar cells with a thin CdS layer, ZnO window layer has been replaced by a suitable thin oxide layer as an intermediate buffer layer. By the proposed oxides, the band alignment between the CIGS layer and the adjacent layer is optimized, while pinholes occurred. It is found that the proposed buffer-less CIGS solar cell leading to the efficiency improvement from 17.6 % to 18.8%.

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Investigation of recombination mechanisms of CdTe solar cells with different buffer layers

Cited by 21 publications

References 33 publications

Impact of CdCl2 Treatment in CdTe Thin Film Grown on Ultra-Thin Glass Substrate via Close Spaced Sublimation

Impact of CdCl2 Treatment in CdTe Thin Film Grown on Ultra-Thin Glass Substrate via Close Spaced Sublimation

Properties of CdSe1−xSx films by magnetron sputtering and their role in CdTe solar cells

Thin oxide buffer layers for avoiding leaks in CIGS solar cells; a theoretical analysis

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