Investigating the Effect of Carbon Nanotube Diameter and Wall Number in Carbon Nanotube/Silicon Heterojunction Solar Cells

Investigating the stability of Ni and Fe nanoparticle distribution and the MWCNT structure in the dry reforming of methane

Catalysts based on Ni and Fe nanoparticles deposited selectively on carbon nanotubes were investigated before and after the dry methane reforming. Three catalysts were synthesized and evaluated, varying the concentration of Ni inside and Fe outside the carbon tubes. BET analysis revealed that the acid treatment opened the ends of the nanotubes and resulted in a higher surface area. Transmission electron microscopy (TEM) showed 24 layers with inner diameter ranging from 4 to 6 nm and outer diameter ranging from 16 to 22 nm. Raman spectroscopy confirmed that after calcination at high temperature the structure of the nanotubes was maintained. X-ray diffraction (XRD) analysis of the catalysts confirmed the presence of NiO (2.6-3.2 nm) and Fe2O3 (4.3 nm) crystallites. The catalytic tests presented high activity in dry methane reform (DRM). The catalysts 10Ni@CNT and 10Ni@CNT/5Fe presented conversions of CH4 (63 and 67%) and CO2 (72 and 88%), respectively, at 800 °C, under atmospheric pressure. Analysis after the reaction showed an increasing ratio of ID/IG, which indicates the formation of defects. The Raman analysis showed that even after calcination at high temperatures the structures of the nanotubes were mostly preserved, and TEM images showed that during the reaction, there were formation of nanotubes occurring randomly.

Optimization and Performance Analysis of a TiO2/i-CH3NH3SnBr3/CsPbI3/Al(BSF) Heterojunction Perovskite Solar Cell for Enhanced Efficiency

This paper reports the simulation and optimization of heterojunction perovskite solar cells (PSCs) with a proposed structure of TiO2/i-CH3NH3SnBr3/CsPbI3/Al(BSF) using SCAPS-1D software. The purpose of this study is to investigate the performance of the PSC with CsPbI3 perovskite active layers and i-CH3NH3SnBr3 as the permeable layer. Therefore, the thicknesses of the layers of the heterojunction perovskite are modified in order to find a better conversion efficiency of the solar cell, where the latter's performance is improved by optimizing the absorber's thickness, which is found to be 1 μm, with a permeable layer of 15 μm. The device efficiency of the i-CH3NH3SnBr3/CsPbI3 heterojunction is improved to 38.98%, and optimized parameters are Voc = 1.21 mV, Jsc = 35.63 mA/cm2, and FF = 89.84%. The acceptor concentration (Na), donor concentration (Nd), defect density, and series and shunt resistances are also investigated.

Recent Insights and Multifactorial Applications of Carbon Nanotubes

Nanotechnology has undergone significant development in recent years, particularly in the fabrication of sensors with a wide range of applications. The backbone of nanotechnology is nanostructures, which are determined on a nanoscale. Nanoparticles are abundant throughout the universe and are thought to be essential building components in the process of planet creation. Nanotechnology is generally concerned with structures that are between 1 and 100 nm in at least one dimension and involves the production of materials or electronics that are that small. Carbon nanotubes (CNTs) are carbon-based nanomaterials that have the structure of tubes. Carbon nanotubes are often referred to as the kings of nanomaterials. The diameter of carbon is determined in nanometers. They are formed from graphite sheets and are available in a variety of colors. Carbon nanotubes have a number of characteristics, including high flexibility, good thermal conductivity, low density, and chemical stability. Carbon nanotubes have played an important part in nanotechnology, semiconductors, optical and other branches of materials engineering owing to their remarkable features. Several of the applications addressed in this review have already been developed and used to benefit people worldwide. CNTs have been discussed in several domains, including industry, construction, adsorption, sensors, silicon chips, water purifiers, and biomedical uses, to show many treatments such as injecting CNTs into kidney cancers in rats, drug delivery, and directing a near-infrared laser at the cancers. With the orderly development of research in this field, additional therapeutic modalities will be identified, mainly for dispersion and densification techniques and targeted drug delivery systems for managing and curing posterior cortical atrophy. This review discusses the characteristics of carbon nanotubes as well as therapeutic applications such as medical diagnostics and drug delivery.

Bias Tunable Photocurrent in Metal-Insulator-Semiconductor Heterostructures with Photoresponse Enhanced by Carbon Nanotubes

Metal-insulator-semiconductor-insulator-metal (MISIM) heterostructures, with rectifying current-voltage characteristics and photosensitivity in the visible and near-infrared spectra, are fabricated and studied. It is shown that the photocurrent can be enhanced by adding a multi-walled carbon nanotube film in the contact region to achieve a responsivity higher than 100   mA   W - 1 under incandescent light of 0.1   mW   cm - 2 . The optoelectrical characteristics of the MISIM heterostructures are investigated at lower and higher biases and are explained by a band model based on two asymmetric back-to-back Schottky barriers. The forward current of the heterojunctions is due to majority-carrier injection over the lower barrier, while the reverse current exhibits two different conduction regimes corresponding to the diffusion of thermal/photo generated carriers and majority-carrier tunneling through the higher Schottky barrier. The two conduction regimes in reverse bias generate two plateaus, over which the photocurrent increases linearly with the light intensity that endows the detector with bias-controlled photocurrent.

Carbon Nanotube Bridging Method for Hole Transport Layer-Free Paintable Carbon-Based Perovskite Solar Cells

The incredible stability of carbon-based perovskite solar cells (C-PSCs) has aroused enormous interest. However, for the paintable C-PSCs, the fill factor (FF) and power conversion efficiency (PCE) remain low, which is because of the insufficient contact at the interface between the perovskite and the electrode and the low conductivity of the electrode. In this work, a carbon nanotube (CNT) bridging method is introduced into the devices by adding single-walled CNTs (SWCNTs) in both perovskite and carbon layers to form a high-quality perovskite/carbon interface. The CNT bridges penetrating into both the CH₃NH₃PbI₃ layer and the carbon cathode not only facilitate charge extraction and transport between the two layers but also promote the electrical conductivity of the carbon electrode. The hole transport layer-free C-PSC with a structure of fluorine-doped tin oxide/compact TiO₂/mesoporous TiO₂/CH₃NH₃PbI₃-SWCNT/SWCNT-C gained a remarkable PCE of 15.73% with an FF of 0.72, accompanied by an outstanding stability of 90 days in the dark under high-humidity [65 ± 5% relative humidity (RH), 25 ± 5 °C] and high-temperature (75 ± 5 °C, 25 ± 5% RH) conditions. The low-cost fabrication process makes highly stable and efficient C-PSCs promising candidates for future applications.

Wavelength-dependent photoconductivity of single-walled carbon nanotube layers

A number of electronic devices such as phase shifters, polarizers, modulators, and power splitters are based on tunable materials. These materials often do not meet all the requirements namely low losses, fast response time, and technological compatibility. Novel nanomaterials, such as single-walled carbon nanotubes, are therefore widely studied to fill this technological gap. Here we show how the dielectric constant of single-walled carbon nanotube layers can be substantially modified by illuminating them due to unique light–matter interactions. We relate the optical excitation of the nanotube layers to the illumination wavelength and intensity, by resistance and capacitance measurements. The dielectric constant is modified under laser illumination due to the change of material polarization and free carrier generation, and is shown to not be temperature-related. The findings indicate that SWCNT layers are a prospective tunable optoelectronic material for both high and low frequency applications.

The optically-tunable dielectric properties of single-walled carbon nanotube layers are wavelength-dependent.

Synthesis of Carbon Nanotube Arrays with High Aspect Ratio via Ni-Catalyzed Pyrolysis of Waste Polyethylene

Carbon nanotube (CNT) arrays 30–50 nm in diameter and with a length of several micrometers were prepared by catalytic pyrolysis of waste polyethylene in Ar at 773−1073 K using nickel dichloride as a catalyst precursor. X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectrometry (Raman), a vibrating-sample magnetometer (VSM), and nitrogen adsorption/desorption were used to investigate the effects of the pyrolysis temperature and catalyst contents on the preparation of the aligned CNTs. As results, the as-obtained CNTs had an outer diameter of 30 nm, a wall thickness of 10 nm, and a length of about 50 μm, and their aspect ratio was high up to 1500. The aligned CNTs containing 0.75 wt% Ni prepared at 973 K exhibited good adsorption performance for methylene blue (MB); furthermore, benefiting from the special magnetic properties of residual Ni catalysts, the as-obtained CNTs could be easily magnetically recycled from the treated solution after adsorption.

Optimization of Synthesis Conditions of Carbon Nanotubes via Ultrasonic-Assisted Floating Catalyst Deposition Using Response Surface Methodology

The growing use of carbon nanotubes (CNTs) in a plethora of applications has provided to us a motivation to investigate CNT synthesis by new methods. In this study, ultrasonic-assisted chemical vapor deposition (CVD) method was employed to synthesize CNTs. The difficulty of controlling the size of clusters and achieving uniform distribution—the major problem in previous methods—was solved by using ultrasonic bath and dissolving ferrocene in xylene outside the reactor. The operating conditions were optimized using a rotatable central composite design (CCD), which helped optimize the operating conditions of the method. Response surface methodology (RSM) was used to analyze these experiments. Using statistical software was very effective, considering that it decreased the number of experiments needed to achieve the optimum conditions. Synthesis of CNTs was studied as a function of three independent parameters viz. hydrogen flow rate (120⁻280 cm³/min), catalyst concentration (2⁻6 wt %), and synthesis temperature (800⁻1200 °C). Optimum conditions for the synthesis of CNTs were found to be 3.78 wt %, 184 cm³/min, and 976 °C for catalyst concentration, hydrogen flow rate, and synthesis temperature, respectively. Under these conditions, Raman spectrum indicates high values of (I_G/I_D), which means high-quality CNTs.

Efficiency Improvement Using Molybdenum Disulphide Interlayers in Single-Wall Carbon Nanotube/Silicon Solar Cells

Molybdenum disulphide (MoS₂) is one of the most studied and widely applied nanomaterials from the layered transition-metal dichalcogenides (TMDs) semiconductor family. MoS₂ has a large carrier diffusion length and a high carrier mobility. Combining a layered structure of single-wall carbon nanotube (SWCNT) and MoS₂ with n-type silicon (n-Si) provided novel SWCNT/n-Si photovoltaic devices. The solar cell has a layered structure with Si covered first by a thin layer of MoS₂ flakes and then a SWCNT film. The films were examined using scanning electron microscopy, atomic force microscopy and Raman spectroscopy. The MoS₂ flake thickness ranged from 5 to 90 nm while the nanosheet’s lateral dimensions size ranged up to 1 μm². This insertion of MoS₂ improved the photoconversion efficiency (PCE) of the SWCNT/n-Si solar cells by approximately a factor of 2.

Direct-Patterning SWCNTs Using Dip Pen Nanolithography for SWCNT/Silicon Solar Cells

Dip pen nanolithography (DPN) is used to pattern single-walled carbon nanotube (SWCNT) lines between the n-type Si and SWCNT film in SWCNT/Si solar cells. The SWCNT ink composition, loading, and DPN pretreatment are optimized to improve patterning. This improved DPN technique is then used to successfully pattern >1 mm long SWCNT lines consistently. This is a 20-fold increase in the previously reported direct-patterning of SWCNT lines using the DPN technique, and demonstrates the scalability of the technique to pattern larger areas. The degree of the uniformity of SWCNTs in these lines is further characterized by Raman spectroscopy and scanning electron microscopy. The patterned SWCNT lines are used as thin conductive pathways in SWCNT/Si solar cells, similar to front contact electrodes. The critical parameters of these solar cells are measured and compared to control cells without SWCNT lines. The addition of SWCNT lines increases power conversion efficiency by 40% (relative). Importantly, the SWCNT lines reduce average series resistance by 44%, and consequently increase average fill factor by 24%.

Charge Transfer from Carbon Nanotubes to Silicon in Flexible Carbon Nanotube/Silicon Solar Cells

Mechanical fragility and insufficient light absorption are two major challenges for thin flexible crystalline Si-based solar cells. Flexible hybrid single-walled carbon nanotube (SWNT)/Si solar cells are demonstrated by applying scalable room-temperature processes for the fabrication of solar-cell components (e.g., preparation of SWNT thin films and SWNT/Si p-n junctions). The flexible SWNT/Si solar cells present an intrinsic efficiency ≈7.5% without any additional light-trapping structures. By using these solar cells as model systems, the charge transport mechanisms at the SWNT/Si interface are investigated using femtosecond transient absorption. Although primary photon absorption occurs in Si, transient absorption measurements show that SWNTs also generate and inject excited charge carriers to Si. Such effects can be tuned by controlling the thickness of the SWNTs. Findings from this study could open a new pathway for designing and improving the efficiency of photocarrier generation and absorption for high-performance ultrathin hybrid SWNT/Si solar cells.

The effect of dry shear aligning of nanotube thin films on the photovoltaic performance of carbon nanotube-silicon solar cells

Recent results in the field of carbon nanotube-silicon solar cells have suggested that the best performance is obtained when the nanotube film provides good coverage of the silicon surface and when the nanotubes in the film are aligned parallel to the surface. The recently developed process of dry shear aligning - in which shear force is applied to the surface of carbon nanotube thin films in the dry state, has been shown to yield nanotube films that are very flat and in which the surface nanotubes are very well aligned in the direction of shear. It is thus reasonable to expect that nanotube films subjected to dry shear aligning should outperform otherwise identical films formed by other processes. In this work, the fabrication and characterisation of carbon nanotube-silicon solar cells using such films is reported, and the photovoltaic performance of devices produced with and without dry shear aligning is compared.

Nanostructured Solar Cells

We are glad to announce the Special Issue "Nanostructured Solar Cells", published in Nanomaterials. This issue consists of eight articles, two communications, and one review paper, covering major important aspects of nanostructured solar cells of varying types. From fundamental physicochemical investigations to technological advances, and from single junction solar cells (silicon solar cell, dye sensitized solar cell, quantum dots sensitized solar cell, and small molecule organic solar cell) to tandem multi-junction solar cells, all aspects are included and discussed in this issue to advance the use of nanotechnology to improve the performance of solar cells with reduced fabrication costs.