Enhanced Carrier Collection in Cd/In-Based Dual Buffers in Kesterite Thin-Film Solar Cells from Nanoparticle Inks
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ABSTRACT:
SUBMITTER: Campbell S
PROVIDER: S-EPMC10646902 | biostudies-literature | 2023 Oct
REPOSITORIES: biostudies-literature
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Project description:Cadmium sulfide (CdS) buffer layer is commonly used in Kesterite Cu2 ZnSn(S,Se)4 (CZTSSe) thin film solar cells. However, the toxicity of Cadmium (Cd) and perilous waste, which is generated during the deposition process (chemical bath deposition), and the narrow bandgap (≈2.4 eV) of CdS restrict its large-scale future application. Herein, the atomic layer deposition (ALD) method is proposed to deposit zinc-tin-oxide (ZTO) as a buffer layer in Ag-doped CZTSSe solar cells. It is found that the ZTO buffer layer improves the band alignment at the Ag-CZTSSe/ZTO heterojunction interface. The smaller contact potential difference of the ZTO facilitates the extraction of charge carriers and promotes carrier transport. The better p-n junction quality helps to improve the open-circuit voltage (VOC ) and fill factor (FF). Meanwhile, the wider bandgap of ZTO assists to transfer more photons to the CZTSSe absorber, and more photocarriers are generated thus improving short-circuit current density (Jsc). Ultimately, Ag-CZTSSe/ZTO device with 10 nm thick ZTO layer and 5:1 (Zn:Sn) ratio, Sn/(Sn + Zn): 0.28 deliver a superior power conversion efficiency (PCE) of 11.8%. As far as it is known that 11.8% is the highest efficiency among Cd-free kesterite thin film solar cells.
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Project description:This manuscript investigates the efficient synthesis of copper zinc tin sulfide (CZTS) nanoparticles for CZTS thin film solar cell applications with a primary focus on environmental sustainability. Underpinning the investigation is an initial life-cycle assessment (LCA) analysis. This LCA analysis is conducted to evaluate the environmental impact of different synthesis volumes, providing crucial insights into the sustainability of the synthesis process by considering the flows of material and energy associated with the process. Life-cycle assessment results demonstrate that significant reductions to the environmental impact can be made by increasing the synthesis volume of CZTS nanoparticle ink. Using a 5-fold increase in volume can reduce all 11 investigated environmental impacts by up to 35.6%, six of these impacts demonstrating reductions >10% and the amount of global warming potential is reduced by 21.4%. Motivated by the LCA results, COMSOL simulations are employed to understand the fluid flow patterns in large-scale fabrication. Various sizes and speeds of stirrer bars are investigated in these simulations, and it is determined that a 50 mm stir bar at 200 rpm represents the optimal configuration for the synthesis process in a 500 mL flask. Subsequently, large-batch CZTS nanoparticle inks are synthesized using these parameters and compared to small-batch samples. The light absorbers are characterized using Raman spectroscopy and X-ray diffraction, confirming favorable properties with close-to-ideal elemental ratios in large-batch synthesis. Finally, solar cell devices fabricated utilizing CZTSSe absorbers from the large volume synthesis process demonstrate comparable performance to those fabricated using small-batch synthesis, with uniform power conversion efficiencies of around 5% across the substrate. This study highlights the potential of large-volume CZTS nanoparticle synthesis for efficient and environmentally friendly CZTS solar cell fabrication, contributing to the advancement of sustainable renewable energy technologies.
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Project description:Solar cells play an increasing role in global electricity production, and it is critical to maximize their conversion efficiency to ensure the highest possible production. The number of photons entering the absorbing layer of the solar cell plays an important role in achieving a high conversion efficiency. Metal nanoparticles supporting localized surface plasmon resonances (LSPRs) have for years been suggested for increasing light in-coupling for solar cell applications. However, most studies have focused on materials exhibiting strong LSPRs, which often come with the drawback of considerable light absorption within the solar spectrum, limiting their applications and widespread use. Recently, aluminum (Al) nanoparticles have gained increasing interest due to their tuneable LSPRs in the ultraviolet and visible regions of the spectrum. In this study, we present an ideal configuration for maximizing light in-coupling into a standard textured crystalline silicon (c-Si) solar cell by determining the optimal Al nanoparticle and anti-reflection coating (ARC) parameters. The best-case parameters increase the number of photons absorbed by up to 3.3%. We give a complete description of the dominating light-matter interaction mechanisms leading to the enhancement and reveal that the increase is due to the nanoparticles optically exhibiting both particle- and thin-film characteristics, which has not been demonstrated in earlier works.
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Project description:Bandgap gradient is a proven approach for improving the open-circuit voltages (VOCs) in Cu(In,Ga)Se2 and Cu(Zn,Sn)Se2 thin-film solar cells, but has not been realized in Cd(Se,Te) thin-film solar cells, a leading thin-film solar cell technology in the photovoltaic market. Here, we demonstrate the realization of a bandgap gradient in Cd(Se,Te) thin-film solar cells by introducing a Cd(O,S,Se,Te) region with the same crystal structure of the absorber near the front junction. The formation of such a region is enabled by incorporating oxygenated CdS and CdSe layers. We show that the introduction of the bandgap gradient reduces the hole density in the front junction region and introduces a small spike in the band alignment between this and the absorber regions, effectively suppressing the nonradiative recombination therein and leading to improved VOCs in Cd(Se,Te) solar cells using commercial SnO2 buffers. A champion device achieves an efficiency of 20.03% with a VOC of 0.863 V.
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Project description:Electrodeposition (ED) technology is a low-cost industrial candidate for solar cell fabrication. However, the practical aspects of controlling deposit morphology and composition have not been significantly addressed because of the complex co-plating variables that still need to be understood for multinary alloy ED. This work addresses these practical aspects on how to control composition and deposit morphology using co-electrodeposited kesterite alloy precursors as a case study. The alloy precursors co-plated under the optimized conditions from a mixed thiosulfate-sulfite electrolyte bath show uniform, smooth, and compact film morphology as well as uniform distribution of composition, well suited for efficient kesterite absorbers, finally delivering a Cu2ZnSnS4 (CZTS) thin-film solar cell with 7.4% efficiency based on a configuration Mo/CZTS/CdS/ZnO/aluminum-doped ZnO. This work underscores that alloy ED, with the advantage of controllable composition and morphology, holds promise for low-cost industrial manufacture of thin-film solar cells.
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Project description:Organic-inorganic halide perovskites have emerged as one of the most promising materials for photovoltaic applications. Because of the polycrystalline nature of perovskite thin films, it is crucial to investigate the impact of microstructures on device performance. In this study, we employ ramp-annealing to tailor the texture of perovskite thin films via controlling the nucleation of perovskite grains. Electrochemical impedance spectroscopy studies further suggest that the thin film texture impacts not only the charge collection at the contact but also the carrier transport in the bulk perovskite layer. The combination of the two effects leads to enhanced performance in devices constructed of preferentially oriented perovskite thin films.
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Project description:For successful long-term deployment and operation of kesterites Cu2ZnSn(S x Se1-x )4 (CZTSSe) as light-absorber materials for photovoltaics, device stability and recovery in kesterite solar cells are investigated. A low-temperature heat treatment is applied to overcome the poor charge extraction that developed in the natural aging process. It is suggested that defect states at aged CZTSSe/CdS heterojunctions were reduced, while apparent doping density in the CZTSSe absorber increased due to Cd/Zn interdiffusion at the heterojunction during the annealing process. In situ annealing experiments in a transmission electron microscope were used to investigate the elemental diffusion at the CZTSSe/CdS heterojunction. This study reveals the critical role of heat treatment to enhance the absorber/Mo back contact, improve the quality of the absorber/buffer heterojunction, and recover the device performance in aged kesterite thin-film solar cells.
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Project description:The formation of molybdenum diselenide (MoSe2) is widely observed at the back-contact interface for copper zinc tin selenide (CZTSe) thin-film solar cells. Depending on individual selenium (Se) supply and thermal conditions for forming CZTSe absorbers on molybdenum (Mo) substrates, the thickness of MoSe2 can vary from a few hundreds of nanometers up to ≈ 1 μm, which is comparable to the commonly adopted thickness of 1 ~ 1.5 μm for CZTSe absorbers. In this study, for controlling the thickness of interfacial MoSe2, thin diffusion barrier layers of silicon oxynitride (SiOxNy) are deposited onto Mo layers prior to the growth of CZTSe absorbers in the fabrication process. As a result, a reduction in the thicknesses of MoSe2 layers is achieved. In terms of energy conversion efficiency (η), CZTSe solar cells grown on Mo/SiOxNy back contacts suffer a deterioration as the SiOxNy layers get thicker. CZTSe solar cells grown on Mo/SiOxNy/Mo back contacts preserve their efficiencies at ≈ 11% with thin 10 nm SiOxNy layers.
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Project description:In this work, the working performance of Platinum (Pt), solvent-free nanoparticle (NP)-based strain sensors made on a flexible substrate has been studied. First, a new model has been developed in order to explain sensor behaviour under strain in a more effective manner than what has been previously reported. The proposed model also highlights the difference between sensors based on solvent-free and solvent-based NPs. As a second step, the ability of atomic layer deposition (ALD) developed Al2O3 (alumina) thin films to act as protective coatings against humidity while in adverse conditions (i.e., variations in relative humidity and repeated mechanical stress) has been evaluated. Two different alumina thicknesses (5 and 11 nm) have been tested and their effect on protection against humidity is studied by monitoring sensor resistance. Even in the case of adverse working conditions and for increased mechanical strain (up to 1.2%), it is found that an alumina layer of 11 nm provides sufficient sensor protection, while the proposed model remains valid. This certifies the appropriateness of the proposed strain-sensing technology for demanding applications, such as e-skin and pressure or flow sensing, as well as the possibility of developing a comprehensive computational tool for NP-based devices.
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Project description:Cu₂ZnSnS₄ (CZTS) is a promising candidate material for photovoltaic applications; hence, ecofriendly methods are required to fabricate CZTS films. In this work, we fabricated CZTS nanocrystal inks by a wet ball milling method, with the use of only nontoxic solvents, followed by filtration. We performed centrifugation to screen the as-milled CZTS and obtain nanocrystals. The distribution of CZTS nanoparticles during centrifugation was examined and nanocrystal inks were obtained after the final centrifugal treatment. The as-fabricated CZTS nanocrystal inks were used to deposit CZTS precursors with precisely controlled CZTS films by a spin-coating method followed by a rapid high pressure sulfur annealing method. Both the grain growth and crystallinity of the CZTS films were promoted and the composition was adjusted from S poor to S-rich by the annealing. XRD and Raman characterization showed no secondary phases in the annealed film, the absence of the detrimental phases. A solar cell efficiency of 6.2% (open circuit voltage: Voc = 633.3 mV, short circuit current: Jsc = 17.6 mA/cm², and fill factor: FF = 55.8%) with an area of 0.2 cm² was achieved based on the annealed CZTS film as the absorber layer.
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