Munkhbayar Batmunkh

Phosphorene and Phosphorene-Based Materials - Prospects for Future Applications.

Phosphorene, a single- or few-layered semiconductor material obtained from black phosphorus, has recently been introduced as a new member of the family of two-dimensional (2D) layered materials. Since its discovery, phosphorene has attracted significant attention, and due to its unique properties, is a promising material for many applications including transistors, batteries and photovoltaics (PV). However, based on the current progress in phosphorene production, it is clear that a lot remains to be explored before this material can be used for these applications. After providing a comprehensive overview of recent advancements in phosphorene synthesis, advantages and challenges of the currently available methods for phosphorene production are discussed. An overview of the research progress in the use of phosphorene for a wide range of applications is presented, with a focus on enabling important roles that phosphorene would play in next-generation PV cells. Roadmaps that have the potential to address some of the challenges in phosphorene research are examined because it is clear that the unprecedented chemical, physical and electronic properties of phosphorene and phosphorene-based materials are suitable for various applications, including photovoltaics.

Carbon Nanotubes for Dye‐Sensitized Solar Cells

As one type of emerging photovoltaic cell, dye-sensitized solar cells (DSSCs) are an attractive potential source of renewable energy due to their eco-friendliness, ease of fabrication, and cost effectiveness. However, in DSSCs, the rarity and high cost of some electrode materials (transparent conducting oxide and platinum) and the inefficient performance caused by slow electron transport, poor light-harvesting efficiency, and significant charge recombination are critical issues. Recent research has shown that carbon nanotubes (CNTs) are promising candidates to overcome these issues due to their unique electrical, optical, chemical, physical, as well as catalytic properties. This article provides a comprehensive review of the research that has focused on the application of CNTs and their hybrids in transparent conducting electrodes (TCEs), in semiconducting layers, and in counter electrodes of DSSCs. At the end of this review, some important research directions for the future use of CNTs in DSSCs are also provided.

Dye-Sensitized Solar Cell Counter Electrodes Based on Carbon Nanotubes

Dye-sensitized solar cells (DSSCs) have received significant attention from the scientific community since their discovery in 1991. However, the high cost and scarcity of platinum has motivated researchers to seek other suitable materials for the counter electrode of DSSCs. Owing to their exceptional properties such as high conductivity, good electrochemical activity, and low cost, carbon nanotubes (CNTs) have been considered as promising alternatives to expensive platinum (Pt) in the counter electrode of DSSCs. Herein, we provide a Minireview of the CNTs use in the counter electrode of DSSCs. A brief overview of Pt-based counter electrodes is also discussed. Particular attention is given to the recent advances of counter electrodes with CNT-based composite structures.

Solution processed graphene structures for perovskite solar cells

Organometallic trihalide perovskite light absorber based solar cells have drawn increasing attention because of their recent rapid increase in power conversion efficiency (PCE). These photovoltaic cells have relied significantly on transparent conducting oxide (TCO) electrodes which are costly and brittle. Herein, solution processed transparent conductive graphene films (TCGFs) are utilized, for the first time, as an alternative to traditional TCO electrodes at the electron collecting layer in perovskite solar cells (PSCs). By investigating and optimizing the trade-off between transparency and sheet resistance (Rs) of the graphene films, a PCE of 0.62% is achieved. This PCE is further improved to 0.81% by incorporating graphene structures into both compact and mesoporous TiO2 layers of the solar cell. We anticipate that the present study will lead to further work to develop graphene-based transparent conductive electrodes for future solar cell devices.

Carbonaceous Dye-Sensitized Solar Cell Photoelectrodes

High photovoltaic efficiency is one of the most important keys to the commercialization of dye sensitized solar cells (DSSCs) in the quickly growing renewable electricity generation market. The heart of the DSSC system is a wide bandgap semiconductor based photoelectrode film that helps to adsorb dye molecules and transport the injected electrons away into the electrical circuit. However, charge recombination, poor light harvesting efficiency and slow electron transport of the nanocrystalline oxide photoelectrode film are major issues in the DSSCs performance. Recently, semiconducting composites based on carbonaceous materials (carbon nanoparticles, carbon nanotubes (CNTs), and graphene) have been shown to be promising materials for the photoelectrode of DSSCs due to their fascinating properties and low cost. After a brief introduction to development of nanocrystalline oxide based films, this Review outlines advancements that have been achieved in the application of carbonaceous‐based materials in the photoelectrode of DSSCs and how these advancements have improved performance. In addition, several of the unsolved issues in this research area are discussed and some important future directions are also highlighted.

Carbon Nanotubes in TiO2 Nanofiber Photoelectrodes for High‐Performance Perovskite Solar Cells

1D semiconducting oxides are unique structures that have been widely used for photovoltaic (PV) devices due to their capability to provide a direct pathway for charge transport. In addition, carbon nanotubes (CNTs) have played multifunctional roles in a range of PV cells because of their fascinating properties. Herein, the influence of CNTs on the PV performance of 1D titanium dioxide nanofiber (TiO2 NF) photoelectrode perovskite solar cells (PSCs) is systematically explored. Among the different types of CNTs, single‐walled CNTs (SWCNTs) incorporated in the TiO2 NF photoelectrode PSCs show a significant enhancement (≈40%) in the power conversion efficiency (PCE) as compared to control cells. SWCNTs incorporated in TiO2 NFs provide a fast electron transfer within the photoelectrode, resulting in an increase in the short‐circuit current (J sc) value. On the basis of our theoretical calculations, the improved open‐circuit voltage (V oc) of the cells can be attributed to a shift in energy level of the photoelectrodes after the introduction of SWCNTs. Furthermore, it is found that the incorporation of SWCNTs into TiO2 NFs reduces the hysteresis effect and improves the stability of the PSC devices. In this study, the best performing PSC device constructed with SWCNT structures achieves a PCE of 14.03%.

Single-Walled Carbon Nanotubes Enhance the Efficiency and Stability of Mesoscopic Perovskite Solar Cells

Carbon nanotubes are 1D nanocarbons with excellent properties and have been extensively used in various electronic and optoelectronic device applications including solar cells. Herein, we report a significant enhancement in the efficiency and stability of perovskite solar cells (PSCs) by employing single-walled carbon nanotubes (SWCNTs) in the mesoporous photoelectrode. It was found that SWCNTs provide both rapid electron transfer and advantageously shifts the conduction band minimum of the TiO2 photoelectrode and thus enhances all photovoltaic parameters of PSCs. The TiO2-SWCNTs photoelectrode based PSC device exhibited a power conversion efficiency (PCE) of up to 16.11%, while the device fabricated without SWCNTs displayed an efficiency of 13.53%. More importantly, we found that the SWCNTs in the TiO2 nanoparticles (TiO2 NPs) based photoelectrode suppress the hysteresis behavior and significantly enhance both the light and long-term storage stability of the PSC devices. The present work provides important guidance for future investigations in utilizing carbonaceous materials for solar cells.

Plasmonic Gold Nanostars Incorporated into High-Efficiency Perovskite Solar Cells

Incorporating appropriate plasmonic nanostructures into photovoltaic (PV) systems is of great utility for enhancing photon absorption and thus improving device performance. Herein, the successful integration of plasmonic gold nanostars (AuNSs) into mesoporous TiO2 photoelectrodes for perovskite solar cells (PSCs) is reported. The PSCs fabricated with TiO2 -AuNSs photoelectrodes exhibited a device efficiency of up to 17.72 %, whereas the control cells without AuNSs showed a maximum efficiency of 15.19 %. We attribute the origin of increased device performance to enhanced light absorption and suppressed charge recombination.

Application of a hole transporting organic interlayer in graphene oxide/single walled carbon nanotube–silicon heterojunction solar cells

The solid-state hole transporting material 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) has been applied as an interlayer for graphene oxide/single walled carbon nanotube–silicon (GOCNT/Si) heterojunction solar cells, forming a GOCNT/spiro-OMeTAD/Si structure. An organic–aqueous transfer method was developed to deposit the GOCNT electrode onto the spiro-OMeTAD coated Si surface without dissolving the organic layer. The influence of the thickness of the organic layer and the thin film GOCNT transparent conducting electrodes as well as the doping of the films with gold chloride (AuCl3) on device performance is explored. With the optimized thickness of the spiro-OMeTAD interlayer and the GOCNT electrode with transmittance above 80% at 550 nm, devices with solar power conversion efficiency of 12.83 ± 0.22% have been fabricated. This study reveals that adding a hole-conducting organic interlayer is able to significantly minimize the recombination at the heterojunction interface. In addition to improving performance, the spiro-OMeTAD behaves as a physical protection layer to significantly enhance device stability.

Synthesis of ultra-long hierarchical ZnO whiskers in a hydrothermal system for dye-sensitised solar cells

One-dimensional (1-D) ZnO structures are of great interest for many applications but the direct hydrothermal synthesis of ultra-long ZnO whiskers (>100 μm) remains a great challenge. Herein, we demonstrate the first synthesis of three kinds of ultra-long hierarchical ZnO whiskers, which are defined as ZnO-2 (>100 μm in length), ZnO-3 (>200 μm in length with relatively smooth surface) and ZnO-4 (>200 μm in length with relatively rough surface), via a one-pot hydrothermal process. The maximum length of hierarchical ZnO-4 whiskers can reach up to about 270 μm. The formation of oval-shaped quasi-hollow structural precursors plays a key role for the correct attachment of Zn2+-terminated and O2−-terminated active surfaces, producing well-ordered Zn2+⋯O2⋯Zn2+ bonds, and finally promoting the formation of ultra-long ZnO whiskers with hierarchical structures. When the synthesized ultra-long hierarchical ZnO-4 whiskers are mixed with commercial TiO2 for dye-sensitised solar cells (DSCs), the current density increases significantly from 13.68 mA cm−2 (commercial TiO2) to 16.81 mA cm−2 (TiO2–ZnO hybrid materials). The hybrid materials show a conversion efficiency of 7.95% which is higher as compared to that of commercial TiO2 (5.87%). This interesting performance of a hybrid material sheds light on the possibility of preparing ultra-long hierarchical ZnO whiskers (>100 μm) with tunable lengths through hydrothermal approaches and their application in DSCs.