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1.
Cu 2ZnSnS 4(CZTS) thin‐film solar cell absorbers with different bandgaps can be produced by parameter variation during thermal treatments. Here, the effects of varied annealing time in a sulfur atmosphere and an ordering treatment of the absorber are compared. Chemical changes in the surface due to ordering are examined, and a downshift of the valence band edge is observed. With the goal to obtain different band alignments, these CZTS absorbers are combined with Zn 1?xSn xO y (ZTO) or CdS buffer layers to produce complete devices. A high open circuit voltage of 809 mV is obtained for an ordered CZTS absorber with CdS buffer layer, while a 9.7% device is obtained utilizing a Cd free ZTO buffer layer. The best performing devices are produced with a very rapid 1 min sulfurization, resulting in very small grains. 相似文献
2.
Sulfurization with various atmosphere and postheat treatments has been reported for earth abundant kesterite Cu 2ZnSnS 4 (CZTS) preparation as cost‐effective material for next‐generation solar cells. A full understanding of the nanoscale microstructure and chemistry of CZTS/CdS interface obtained from these different fabrication routes is currently lacking, yet is critical to developing optimal processing routes for high‐performance kesterite solar cells. Here, the first detailed investigation of the interfacial microstructure and chemistry of CdS/Cu 2ZnSnS 4 heterojunctions is presented. For CZTS obtained from sulfurization in a sulfur‐only atmosphere where highly defective surfaces are present, air annealing followed by etching in the initial stage of chemical bath deposition (CBD) process can effectively eliminate interfacial defects and allow the epitaxial growth of CBD‐CdS, improving the minority lifetime, open circuit voltage ( VOC), and fill factor (FF) of the devices, while blocking Cd diffusion and deteriorating short circuit current ( Jsc). For CZTS from sulfurization in a combined sulfur and SnS atmosphere where CBD‐CdS can directly epitaxially grow on CZTS and Cd‐diffusion is clearly observed, associated devices show the longest lifetime and the highest efficiency of 8.76%. Epitaxial growth of CdS and Cd diffusion into CZTS are found to be two crucial features minimizing interfacial recombination and achieving high‐efficiency devices. This will not only enhance the understanding of the device structure and physics of kesterite based solar cells, but also provide an effective way for designing other chalcogenide heterojunction solar cells. 相似文献
3.
The reduction in electronic recombination losses by the passivation of surfaces is a key factor enabling high‐efficiency solar cells. Here a strategy to passivate surface trap states of TiO 2 films used as cathode interlayers in organic photovoltaics (OPVs) through applying alumina (Al 2O 3) or zirconia (ZrO 2) insulating nanolayers by thermal atomic layer deposition (ALD) is investigated. The results suggest that the surface traps in TiO 2 are oxygen vacancies, which cause undesirable recombination and high electron extraction barrier, reducing the open‐circuit voltage and the short‐circuit current of the complete OPV device. It is found that the ALD metal oxides enable excellent passivation of the TiO 2 surface followed by a downward shift of the conduction band minimum. OPV devices based on different photoactive layers and using the passivated TiO 2 electron extraction layers exhibit a significant enhancement of more than 30% in their power conversion efficiencies compared to their reference devices without the insulating metal oxide nanolayers. This is a result of significant suppression of charge recombination and enhanced electron extraction rates at the TiO 2/ALD metal oxide/organic interface. 相似文献
4.
High‐performance Cu 2ZnSnS 4 photovoltaic devices are demonstrated using electrodeposition of metal stacks and annealing of a CuZnSn precursor in a sulfur atmosphere. A champion electroplated Cu 2ZnSnS 4 solar cell achieves a power conversion efficiency of 7.3%, which is a record efficiency for electrodeposited Cu 2ZnSnS 4 solar devices. The device performance points to electrodeposition and annealing as a low‐cost and viable approach to earth‐abundant solar cell fabrication. 相似文献
5.
This study offers new insight into the role of Na in Cu 2ZnSnS 4 (CZTS) thin film solar cells by studying samples with a spatially varying alkali distribution. This is achieved by omitting a diffusion barrier between the soda‐lime glass substrate and the Mo back contact, where compositional variations of the glass inherently result in non‐uniform alkali distributions in the CZTS. By correlating light beam induced current (LBIC) maps with secondary ion mass spectrometry composition maps, it is shown that samples containing regions of higher Na concentration (“hot spots”) have corresponding LBIC hot spots on comparable length scales. Samples containing an alkali diffusion barrier have lower LBIC dispersion; thus, LBIC can be used to evaluate non‐uniformity in CZTS devices, where a common cause is Na inhomogeneity. Moreover, it is shown that the Na hot spots are strongly correlated with other compositional variations in the device, including increased Cu in‐diffusion with the underlying MoS 2 layer and decreased diffusion of Cd to the back contact. Neither of these effects are well understood in CZTS devices, and neither have previously been correlated with the presence or absence of Na. 相似文献
6.
A N, N-dimethylformamide and thiourea-based route is developed to fabricate submicron (0.55 and 0.75 µm) thick CuIn(S,Se) 2 (CISSe) thin films for photovoltaic applications, addressing challenges of material usage, throughput, and manufacturing costs. However, reducing the absorber film thickness below 1 µm in a regular CISSe solar cell decreases the device efficiency due to losses at the highly-recombinative, and mediocre-reflective Mo/CISSe rear interface. For the first time, to mitigate the rear recombination losses, a novel rear contacting structure involving a surface passivation layer and point contact openings is developed for solution processed CISSe films and demonstrated in tangible devices. An atomic layer deposited Al 2O 3 film is employed to passivate the Mo/CISSe rear surface while precipitates formed via chemical bath deposition of CdS are used to generate nanosized point openings. Consequently, Al 2O 3 passivated CISSe solar cells show an increase in the open-circuit voltage (V OC) and short-circuit current density when compared to reference cells with equivalent absorber thicknesses. Notably, a V OC increase of 59 mV contributes to active area efficiencies of 14.2% for rear passivated devices with 0.75 µm thick absorber layers, the highest reported value for submicron-based solution processed, low bandgap CISSe solar cells. 相似文献
7.
Nanolayers of Al 2O 3 and TiO 2 coatings were applied to lithium‐ and manganese‐rich cathode powder Li 1.2Ni 0.13Mn 0.54Co 0.13O 2 using an atomic layer deposition (ALD) method. The ALD coatings exhibited different surface morphologies; the Al 2O 3 surface film appeared to be uniform and conformal, while the TiO 2 layers appeared as particulates across the material surface. In a Li‐cell, the Al 2O 3 surface film was stable during repeated charge and discharge, and this improved the cell cycling stability, despite a high surface impedance. The TiO 2 layer was found to be more reactive with Li and formed a Li xTiO 2 interface, which led to a slight increase in cell capacity. However, the repetitive insertion/extraction process for the Li + ions caused erosion of the surface protective TiO 2 film, which led to degradation in cell performance, particularly at high temperature. For cells comprised of the coated Li 1.2Ni 0.13Mn 0.54Co 0.13O 2 and an anode of meso‐carbon‐micro‐beads (MCMB), the cycling stability introduced by ALD was not enough to overcome the electrochemical instability of MCMB graphite. Therefore, protection of the cathode materials by ALD Al 2O 3 or TiO 2 can address some of the capacity fading issues related to the Li‐rich cathode at room temperature. 相似文献
8.
In the few past years, the economic and eco-friendly Cu2ZnSnS4 (CZTS) solar cells have caught lots of attentions. However, due to rather poor efficiency, identifying deficiencies and making improvements is necessary. In the present study, the performance improvement of ultrathin CZTS solar cells was achieved through (1) incorporation of anti-reflective coating (ARC) on the surface of cell and (2) embedding Al plasmonic nanostructures with different radius, periods, and vertical positions in the absorber layer. Various thicknesses of CZTS absorber layer were simulated optically and electrically using FDTD and DEVICE solver of Lumerical software. The reference solar cell consists of a 1.5-nm-thick CZTS absorber and exhibit an efficiency of up to 5.67%, short-circuit current density (Jsc) of 18.48 mA cm−2 and open circuit voltage of 0.58 V. Result showed a remarkable performance enhancement of the solar cell in spite of a very thin absorber layer. For a 500-μm-thick CZTS solar cell with the assistance of ARC and embedding Al plasmonic nanostructures, the efficiency is increased to 7.45% due to an increase in Jsc to 22.62 mA cm−2 with an open circuit voltage of 0.62 V. 相似文献
9.
Quaternary semiconducting materials based on the kesterite (A 2BCX 4) mineral structure are the most promising candidates to overtake the current generation of light‐absorbing materials for thin‐film solar cells. Cu 2ZnSnS 4 (CZTS), Cu 2ZnSnSe 4 (CZTSe) and their alloy Cu 2ZnSn(Se,S) 4 consist of abundant, low‐cost and non‐toxic elements, unlike current CdTe and Cu(In,Ga)Se 2 based technologies. Zinc‐blende related structures are formed by quaternary compounds, but the complexity associated with the multi‐component system introduces difficulties in material growth, characterization, and application. First‐principles electronic structure simulations, performed over the past five years, that address the structural, electronic, and defect properties of this family of compounds are reviewed. Initial predictions of the bandgaps and crystal structures have recently been verified experimentally. The calculations highlight the role of atomic disorder on the cation sub‐lattice, as well as phase separation of Cu 2ZnSnS 4 into ZnS and CuSnS 3, on the material performance for light‐to‐electricity conversion in photovoltaic devices. Finally, the current grand challenges for materials modeling of thin‐film solar cells are highlighted. 相似文献
10.
Based on an understanding of atomic layer deposition (ALD) from prior experimental and computational results, all-atom molecular dynamics (MD) simulations are used to model the Al 2O 3 film structure and composition during ALD processing. By separating the large time-scale surface reactions from the small time-scale structural relaxation, we have focused on the growth dynamics of amorphous Al 2O 3 films at the atomic scale. The simulations are able to reproduce some important properties and growth mechanisms of Al 2O 3 ALD films, and hence provide a bridge between atomic-level information and experimental measurements. Information about the evolution of the microscopic structures of the Al 2O 3 films is generated, and the influence of operation parameters on the Al 2O 3 ALD process. The simulations predict a strong influence of the initial surface composition and process temperature on the surface roughness, growth rate and growth mode of the deposited films. 相似文献
11.
To alleviate the limitations of pure sulfide Cu 2ZnSnS 4 (CZTS) thin film, such as band gaps adjustment, antisite defects, secondary phase and microstructure, Cadmium is introduced into CZTS thin film to replace Zn partially to form Cu 2Zn 1?xCd xSnS 4 (CZCTS) thin film by low‐cost sol–gel method. It is demonstrated that the band gaps and crystal structure of CZCTS thin films are affected by the change in Zn/Cd ratio. In addition, the ZnS secondary phase can be decreased and the grain sizes can be improved to some degree by partial replacement of Zn with Cd in CZCTS thin film. The power conversion efficiency of CZTS solar cell device is enhanced significantly from 5.30% to 9.24% (active area efficiency 9.82%) with appropriate ratio of Zn/Cd. The variation of device parameter as a function of Zn/Cd ratio may be attributed to the change in electronic structure of the bulk CZCTS thin film (i.e., phase change from kesterite to stannite), which in turn affects the band alignment at the CZCTS/buffer interface and the charge separation at this interface. 相似文献
12.
Atomic layer deposition (ALD) of Al 2O 3 is applied on a polypropylene separator for lithium‐ion batteries. A thin Al 2O 3 layer (<10 nm) is coated on every surface of the porous polymer microframework without significantly increasing the total separator thickness. The thin Al 2O 3 ALD coating results in significantly suppressed thermal shrinkage, which may lead to improved safety of the batteries. More importantly, the wettability of Al 2O 3 ALD‐coated separators in an extremely polar electrolyte based on pure propylene carbonate (PC) solvent is demonstrated, without any decrease in electrochemical performances such as capacity, rate capability, and cycle life. Finally, a LiCoO 2/natural graphite full cell is demonstrated under extremely severe conditions (pure PC‐based electrolyte and high (4.5 V) upper cut‐off potential), which is enabled by the Al 2O 3 ALD coating on all three components (cathode, anode, and separator). 相似文献
13.
It is well‐known that sodium improves the performance of Cu 2ZnSnS 4 (CZTS) devices, yet the mechanism of the enhancement is still not fully understood. This work aims to present a unified account of the relationships between grain boundaries in CZTS, sodium content at these boundaries, non‐radiative recombination, and surfactant effects that produce large microstructural changes. Using temperature‐dependent photoluminescence measurements, it is demonstrated that samples containing dramatically different grain sizes display identical radiative and non‐radiative decay characteristics when sufficient sodium is present in the film. It is also shown that the sodium concentration needed to efficiently passivate non‐radiative defects is significantly less that the quantity needed to obtain micrometer‐sized CZTS grains. Finally, the high densities of donor‐acceptor pairs that are observed in CZTS films appear to reside within the grains themselves, rather than at grain boundaries. 相似文献
14.
As a wide‐bandgap semiconductor, titanium dioxide (TiO 2) with a porous structure has proven useful in dye‐sensitized solar cells, but its application in low‐cost, high‐efficiency inorganic photovoltaic devices based on materials such as Cu(InGa)Se 2 or Cu 2ZnSnS 4 is limited. Here, a thin film made from solution‐processed TiO 2 nanocrystals is demonstrated as an alternative to intrinsic zinc oxide (i‐ZnO) as the window layer of CuInS xSe 1?x solar cells. The as‐synthesized, well‐dispersed, 6 nm TiO 2 nanocrystals are assembled into thin films with controllable thicknesses of 40, 80, and 160 nm. The TiO 2 nanocrystal films with thicknesses of 40 and 80 nm exhibit conversion efficiencies (6.2% and 6.33%, respectively) that are comparable to that of a layer of the typical sputtered i‐ZnO (6.42%). The conversion efficiency of the devices with a TiO 2 thickness of 160 nm decreases to 2.2%, owing to the large series resistance. A 9‐hour reaction time leads to aggregated nanoparticles with a much‐lower efficiency (2%) than that of the well‐dispersed TiO 2 nanoparticles prepared using a 15‐hour reaction time. Under optimized conditions, the champion TiO 2 nanocrystal‐film‐based device shows even higher efficiency (9.2%) than a control device employing a typical i‐ZnO film (8.6%). 相似文献
15.
In order to assess the contributions of anti‐reflective and passivation effects in microstructured silicon‐based solar light harvesting devices, thin layers of aluminum oxide (Al 2O 3), silicon dioxide (SiO 2), silicon‐rich silicon nitride (SiN x), and indium tin oxide (ITO), with a thickness ranging from 45 to 155 nm, are deposited onto regularly packed arrays of silicon micropillars with radial p/n junctions. Atomic layer deposition of Al 2O 3 yields the best conformal coating over the micropillars. The fact that layers made by low‐pressure chemical vapor deposition (SiO 2 and SiN x) are not conformally deposited on the sidewalls of the Si micropillars do not influence the photoelectrical efficiency. For ITO, a change in composition along the micropillar height is measured, which leads to poor performance. For Al 2O 3, deconvolution of the contributions of passivation and anti‐reflection to the overall efficiency gain exhibits the importance of passivation in micro/nano‐structured Si devices. Al 2O 3‐coated samples perform the best, for both n/p and p/n configured pillars, yielding (relative) increases of 116% and 37% in efficiency of coated versus non‐coated samples for p‐type and n‐type base micropillar arrays, respectively. 相似文献
16.
The identification of performance‐limiting factors is a crucial step in the development of solar cell technologies. Cu 2ZnSn(S,Se) 4‐based solar cells have shown promising power conversion efficiencies in recent years, but their performance remains inferior compared to other thin‐film solar cells. Moreover, the fundamental material characteristics that contribute to this inferior performance are unclear. In this paper, the performance‐limiting role of deep‐trap‐level‐inducing 2Cu Zn+Sn Zn defect clusters is revealed by comparing the defect formation energies and optoelectronic characteristics of Cu 2ZnSnS 4 and Cu 2CdSnS 4. It is shown that these deleterious defect clusters can be suppressed by substituting Zn with Cd in a Cu‐poor compositional region. The substitution of Zn with Cd also significantly reduces the bandgap fluctuations, despite the similarity in the formation energy of the Cu Zn+Zn Cu and Cu Cd+Cd Cu antisites. Detailed investigation of the Cu 2CdSnS 4 series with varying Cu/[Cd+Sn] ratios highlights the importance of Cu‐poor composition, presumably via the presence of V Cu, in improving the optoelectronic properties of the cation‐substituted absorber. Finally, a 7.96% efficient Cu 2CdSnS 4 solar cell is demonstrated, which shows the highest efficiency among fully cation‐substituted absorbers based on Cu 2ZnSnS 4. 相似文献
17.
A new charge recombination layer for inverted tandem polymer solar cells is reported. A bilayer of MoO X/Al 2O 3:ZnO nanolaminate is shown to enable efficient charge recombination in inverted tandem cells. A polymer surface modification on the MoO X/Al 2O 3:ZnO nanolaminate bilayer increases the work function contrast between the two outward surfaces of the charge recombination layer, further improving the performance of tandem solar cells. An analysis of the electrical, optical, and surface properties of the charge recombination layer is presented. Inverted tandem polymer solar cells, with two photoactive layers comprising poly (3‐hexylthiophene) (P3HT):indene‐C 60 bisadduct (IC 60BA) for the bottom cell and poly[(4,8‐bis‐(2‐ethylhexyloxy)‐benzo[1,2‐b:4,5‐b']dithiophene)‐2,6‐diyl‐alt‐(4‐(2‐ethylhexanoyl)‐thieno[3,4‐b]thiophene))‐2,6‐diyl] (PBDTTT‐C):[6,6]‐phenyl C 61 butyric acid methyl ester (PC 60BM) for the top cell, yield an open‐circuit voltage of 1481 mV ± 15 mV, a short‐circuit current density of 7.1 mA cm ?2 ± 0.1 mA cm ?2, and a fill factor of 0.62 ± 0.01, resulting in a power conversion efficiency of 6.5% ± 0.1% under simulated AM 1.5G, 100 mW cm ?2 illumination. 相似文献
18.
Functioning quantum dot (QD) sensitized solar cells have been fabricated using the vacuum deposition technique atomic layer deposition (ALD). Utilizing the incubation period of CdS growth by ALD on TiO 2, we are able to grow QDs of adjustable size which act as sensitizers for solid‐state QD‐sensitized solar cells (ssQDSSC). The size of QDs, studied with transmission electron microscopy (TEM), varied with the number of ALD cycles from 1‐10 nm. Photovoltaic devices with the QDs were fabricated and characterized using a ssQDSSC device architecture with 2,2',7,7'‐tetrakis‐(N,N‐di‐p methoxyphenylamine) 9,9'‐spirobifluorene (spiro‐OMeTAD) as the solid‐state hole conductor. The ALD approach described here can be applied to fabrication of quantum‐confined structures for a variety of applications, including solar electricity and solar fuels. Because ALD provides the ability to deposit many materials in very high aspect ratio substrates, this work introduces a strategy by which material and optical properties of QD sensitizers may be adjusted not only by the size of the particles but also in the future by the composition. 相似文献
19.
Metal‐halide perovskites show promise as highly efficient solar cells, light‐emitting diodes, and other optoelectronic devices. Ensuring long‐term stability is now a major priority. In this study, an ultrathin (2 nm) layer of polyethylenimine ethoxylated (PEIE) is used to functionalize the surface of C 60 for the subsequent deposition of atomic layer deposition (ALD) SnO 2, a commonly used electron contact bilayer for p–i–n devices. The enhanced nucleation results in a more continuous initial ALD SnO 2 layer that exhibits superior barrier properties, protecting Cs 0.25FA 0.75Pb(Br 0.20I 0.80) 3 films upon direct exposure to high temperatures (200 °C) and water. This surface modification with PEIE translates to more stable solar cells under aggressive testing conditions in air at 60 °C under illumination. This type of “built‐in” barrier layer mitigates degradation pathways not addressed by external encapsulation, such as internal halide or metal diffusion, while maintaining high device efficiency up to 18.5%. This nucleation strategy is also extended to ALD VO x films, demonstrating its potential to be broadly applied to other metal oxide contacts and device architectures. 相似文献
20.
The morphology and the electronic properties of monocrystalline Si (c‐Si) with a nano‐textured “black” surface, obtained by a metal‐catalyzed wet etching process, and the improvement by an additional chemical treatment are examined with regard to solar cell applications. Photoluminescence and optical reflectivity measurements show the presence of a nano‐porous Si (np‐Si) phase in the as‐prepared nano‐texture. It is found that an additional wet chemical treatment with the standard clean 1 of the common RCA cleaning process removes the np‐Si fraction and significantly alters the surface of the nano‐structure. Cross‐sectional scanning electron microscopy images reveal a pronounced reduction of the surface area, to values of only 3–6 times that of a planar surface. Electron spin resonance measurements were performed to investigate the type and quantity of defects induced by the nano‐texturing process. The optimized nano‐texture exhibits a Si dangling bond density comparable to planar c‐Si wafers. Electrically detected magnetic resonance spectra reveal an additional paramagnetic defect present in the nano‐textured Si, linked to a hydrogen‐ or oxygen‐related double donor. In addition, initial results on the passivation of surface defects via atomic layer deposition of Al 2O 3 are presented. Photoconductance decay measurements of passivated samples show a tenfold increase of the effective lifetime for nano‐textures which have received the additional etching treatment. The improved electronic quality of the nano‐textured surface makes it an interesting candidate for application as an anti‐reflection surface in solar cells. 相似文献
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