Electrically Sorted Single-Walled Carbon Nanotubes-Based Electron Transporting Layers for Perovskite Solar Cells

© 2019 The Author(s). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).Incorporation of as prepared single-walled carbon nanotubes (SWCNTs) into the electron transporting layer (ETL) is an effective strategy to enhance the photovoltaic performance of perovskite solar cells (PSCs). However, the fundamental role of the SWCNT electrical types in the PSCs is not well understood. Herein, we prepared semiconducting (s-) and metallic (m-) SWCNT families and integrated them into TiO2 photoelectrodes of the PSCs. Based on experimental and theoretical studies, we found that the electrical type of the nanotubes plays an important role in the devices. In particular, the mixture of s-SWCNTs and m-SWCNTs (2:1 w/w)-based PSCs exhibited a remarkable efficiency of up to 19.35%, which was significantly higher than that of the best control cell (17.04%). In this class of PSCs, semiconducting properties of s-SWCNTs play a critical role in extracting and transporting electrons, whereas m-SWCNTs provide high conductance throughout the electrode

Emerging 2D layered materials for perovskite solar cells

Perovskite solar cells (PSCs) are now at the forefront of the state-of-the-art photovoltaic technologies due to their high efficiency and low fabrication costs. To further realize the potential of this fascinating class of solar cells, nanostructured functional materials have been playing important roles. 2D layered materials have attracted a great deal of interest due to their fascinating properties and unique structure. Recently, the exploration of a wide range of novel 2D materials for use in PSCs has seen considerable progress, but still a lot remains to be done in this field. In this progress report, the advancements that have recently been made in the application of these emerging 2D materials, beyond graphene, for PSCs are presented. Both the advantages and challenges of these 2D materials for PSCs are highlighted. Finally, important directions for the future advancements toward efficient, low-cost, and stable PSCs are outlined

Synthesis, purification, properties and characterization of sorted single-walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) have attracted significant attention due to their outstanding mechanical, chemical and optoelectronic properties, which makes them promising candidates for use in a wide range of applications. However, as-produced SWCNTs have a wide distribution of various chiral species with different properties (i.e. electronic structures). In order to take full advantage of SWCNT properties, highly purified and well-separated SWCNTs are of great importance. Recent advances have focused on developing new strategies to effectively separate nanotubes into single-chirality and/or semiconducting/metallic species and integrating them into different applications. This review highlights recent progress in this cutting-edge research area alongside the enormous development of their identification and structural characterization techniques. A comprehensive review of advances in both controlled synthesis and post-synthesis separation methods of SWCNTs are presented. The relationship between the unique structure of SWCNTs and their intrinsic properties is also discussed. Finally, important future directions for the development of sorting and purification protocols for SWCNTs are provided

Recent advances in applications of sorted single‐walled carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) exhibit outstanding properties that make them appealing in a wide range of applications. However, their properties are variable depending on the tube helicity (chirality), which has been a challenge for a long time and needs to be effectively controlled. In recent years, tremendous efforts have been made to control the electrical type/chirality of nanotubes through both direct controlled synthesis and postsynthesis separation methods. Driven by these breakthroughs, the applications of separated families of SWCNTs in various fields have emerged as a new topic of research. In this Review, an overview of recent advances in the use of highly purified and well-separated SWCNTs in a comprehensive range of applications is presented including photovoltaics, transistors, batteries, sensors, light emitters, biological/medical fields, and others. Finally, important future directions for the utilization of separated SWCNTs in these fields are provided

Preparation of hybrid molybdenum disulfide/single wall carbon nanotube–n-type silicon solar cells

Carbon nanotube/silicon (CNT/Si) heterojunction solar cells represent one new architecture for photovoltaic devices. The addition of MoS to the devices is shown to increase the efficiency of the devices. Two structures are explored. In one case, the single wall carbon nanotubes (SWCNTs) and MoS flakes are mixed to make a hybrid, which is then used to make a film, while in the other case, a two layer system is used with the MoS deposited first followed by the SWCNTs. In all cases, the solar cell efficiency is improved largely due to significant increases in the fill factor. The rise in fill factor is due to the semiconducting nature of the MoS, which helps with the separation of charge carriers

Ti3C2Tx (MXene)‐silicon heterojunction for efficient photovoltaic cells

A novel type of solar cell has been developed based on charge separation at the heterojunction formed by a transparent conducting MXene electrode and an n-type silicon (n-Si) wafer. A thin layer of the native silicon dioxide plays an important role in suppressing the recombination of charge carriers. A two-step chemical treatment can increase the device efficiency by about 40%. Promisingly, an average power conversion efficiency of over 10% under simulated full sunlight is achieved for this novel class of solar cell with the application of an antireflection layer. The efficiencies of these novel solar cells based on a MXene-Si heterojunction achieved in this work point to great promise in emerging photovoltaic technology. In addition to their high efficiency, the excellent reproducibility of such devices establishes a solid base for possible future commercialization

Few-layer black phosphorus and boron-doped graphene based heteroelectrocatalyst for enhanced hydrogen evolution

Research interest in two-dimensional (2D) materials has grown exponentially across various fields over the past few years. In particular, 2D phosphorene, the single- or few-layered analogue of semiconducting black phosphorus (BP), holds specific promise for advanced catalysis reactions including electrocatalytic hydrogen (H2) production. However, bare phosphorene nanosheets suffer from poor electrical conductivity, limited catalytic sites and instability under ambient conditions. Herein, we integrate ultrathin few-layer BP (FL-BP) nanosheets with boron-doped graphene (BG) to form a novel metal-free 2D/2D heteroelectrocatalyst for the hydrogen evolution reaction (HER) in acidic media. Our newly designed electrocatalyst (FL-BP@BG) shows remarkably enhanced HER activity with a low overpotential of 385.9 mV at 10 mA cm−2, while exhibiting a low charge transfer resistance of only 5.5 Ω in H2SO4\ua0electrolyte. In addition, the FL-BP@BG catalyst shows an outstanding stability over 500 continuous cycles, demonstrating that hybridizing FL-BP with BG is an efficient strategy to construct stable BP based electrocatalyst. This work paves the way for emerging 2D materials for advanced catalysis systems

Efficient Inverted Perovskite Solar Cells Using Dual Fluorinated Additive Modification

Abstract Materials engineering is key to improving the stability and photovoltaic parameters of inverted perovskite solar cells (PSCs). This work presents the effect of two different fluorinated additives on the performance of PSCs containing the archetypal three‐dimensional perovskite, methylammonium lead triiodide (MAPbI3). 3‐(2,3,4,5,6‐Pentafluorophenyl)propylammonium iodide (FPAI) is added to the anode modifying layer and (2,3,4,5,6‐pentafluorophenyl)methylammonium bromide (FMABr) is blended into the perovskite layer. The inverted devices containing FPAI in the anode modifying layer and 0.32 mol% of FMABr from the perovskite precursor solution had hysteresis‐free current density‐voltage characteristics and a maximum power conversion efficiency of 22.3%, which is an absolute increase of 1.7% compared to the MAPbI3 device (20.6%) of the same architecture but without the additives