Query: Mesoporous TiO2 single crystals delivering enhanced mobility and optoelectronic device performance

Candidate papers:

abstract: Mesoporous ceramics and semiconductors enable low cost solar power, solar fuel, (photo)catalyst and electrical energy storage technologies. State of the art, printable high surface area electrodes are fabricated from thermally sintered pre formed nanocrystals. Mesoporosity provides the desired highly accessible surfaces but many applications also demand long range electronic connectivity and structural coherence. A mesoporous single crystal (MSC) semiconductor can meet both criteria. Here we demonstrate a general synthetic method of growing semiconductor MSCs of anatase TiO2 based on seeded nucleation and growth inside a mesoporous template immersed in a dilute reaction solution. We show that both isolated MSCs and ensembles incorporated into films have substantially higher conductivities and electron mobilities than does nanocrystalline TiO2. Conventional nanocrystals, unlike MSCs, require in film thermal sintering to reinforce electronic contact between particles, thus increasing fabrication cost, limiting the use of flexible substrates and precluding, for instance, multijunction solar cell processing. Using MSC films processed entirely below 150 degC, we have fabricated all solid state, low temperature sensitized solar cells that have 7.3 per cent efficiency, the highest efficiency yet reported. These high surface area anatase single crystals will find application in many different technologies, and this generic synthetic strategy extends the possibility of mesoporous single crystal growth to a range of functional ceramics and semiconductors.
author_names: Edward J W Crossland

Nakita K Noel

Varun Sivaram

T Leijtens

Jack A Alexander-Webber

Henry J Snaith
title: Mesoporous TiO2 single crystals delivering enhanced mobility and optoelectronic device performance
venue: Nature
year: 2013

abstract: DOI: 10.1002/ppsc.201800198 past few years for their high aspect ratio (surface to volume ratio) distinctive physicochemical properties compared to the conventional nanostructures. Under equilibrium, {001} facet dominated TiO2 nanostructure is rarely observed as it has very high surface energy (average surface energy of {001} facet (0.90 J m 2) is double that of {101} facet (0.44 J m 2)[14] Thus, during the usual growth process, the less reactive {101} facet is dominated over the highly reactive {001} facet. However, several reports[14 16] have been published on the controlled growth of TiO2 single crystals with exposed {001} facet after the breakthrough work by Yang et al.[17] that demonstrated the hydrothermal synthesis of anatase TiO2 single crystals with 47% exposed {001} facet. Following this work, {001} facet dominated TiO2 microcrystals are being extensively investigated with various doping and photocatalytic applications for environmental cleaning. Recently, mesoporous TiO2 single crystals delivering enhanced mobility and optoelectronic device performance was reported by Crossland et al.[18] Ding et al. reported on mesoporous hollow TiO2 microspheres with enhanced photoluminescence (PL)[19] However, most of these works were carried out using a mesoporous template method and the PL yield was not addressed in these works. To the best of our knowledge, there is no report on fluorine doping of mesoporous TiO2 nanostructure and the extremely high PL quantum yield (QY) of self grown anatase fluorine doped TiO2 (F TiO2) nanocrystals (NCs) on mesoporous F TiO2 flowers. Thus, a detailed study on structural and optical properties of mesoporous F TiO2 nanostructures is warranted to explore its novel properties including high PL QY. With conventional semiconductor quantum dots, chiral quantum dots based cellular imaging, sensing, and biomedical applications are not so encouraging because of the involvement of toxic elements such as cadmium[20] in the chiral composition. This hinders its applicability in living cells and study for nontoxic analogues of these chiral luminescent nanomaterials is of great interest.[21] Recently, Cleary et al.[22] reported on the highly luminescent TiO2 nanoparticles (NPs) with chiral capping ligand having size 30 50 nm with a PL QY up to 3.5% However, the reported PL yields were measured mostly in colloidal solution, where surface functionalization by the solvents Herein a novel approach is reported to achieve tunable and high photoluminescence (PL) quantum yield (QY) from the self grown spherical TiO2 quantum dots (QDs) on fluorine doped TiO2 (F TiO2) flowers, mesoporous in nature, synthesized by a simple solvothermal process. The strong PL emission from F TiO2 QDs centered at 485 nm is associated with shallow and deep traps, and a record high PL QY of 5.76% is measured at room temperature. Size distribution and doping of F TiO2 nanocrystals (NCs) are successfully tuned by simply varying the HF concentration during synthesis. During the post growth rapid thermal annealing (RTA) under vacuum, the arbitrary shaped F TiO2 NCs transform into spherical QDs with smaller sizes and it shows dramatic enhancement (163 times) in the PL intensity. Electron spin resonance (ESR) and X ray photoelectron spectroscopy (XPS) confirm the high density of oxygen vacancy defects on the surface of TiO2 NCs. Confocal fluorescence microscopy imaging shows bright whitish emission from the F TiO2 QDs. Low temperature and time resolved PL studies reveal that the ultrafast radiative recombination in the TiO2 QDs results in highly efficient PL emission. A highly stable, biologically inert, and highly fluorescent TiO2 QDs/flowers without any capping agent demonstrated here is significant for emerging applications in bioimaging, energy, and environmental cleaning. Quantum Dot Photoluminescence
author_names: Kamal Kumar Paul

Subhadip Jana

P K Giri
title: Tunable and High Photoluminescence Quantum Yield from Self Decorated TiO2 Quantum Dots on Fluorine Doped Mesoporous TiO2 Flowers by Rapid Thermal Annealing
year: 2018

abstract: Abstract A rational solvothermal method is proposed to achieve the conversion from a Zn contented metal organic framework to ZnO mesoporous single crystal like spheres. The as prepared ZnO sphere is composed of oriented assembled primary crystals, which exhibits single crystal nature with narrow pore size distribution and high surface area. In addition, time depending trails indicate the metal organic framework functions as reservoir to control the release of Zn species and the organic molecules also serve as directing regent to facilitate the oriented assembling of the ZnO primary units. Thanks to this structure coherence, the ZnO sphere delivers high electron mobility, which enables reduced carrier recombination and improved collection efficiency of the photoelectrons when used as photoanode in CdS/CdSe sensitized solar cell. The device achieves a high power conversion efficiency of ~6.20% which is substantially improved from that of regular ZnO nanoparticles ~5.02% Moreover, when evaluated as anode for lithium ion battery, the ZnO sphere based electrode demonstrates high reversible capacity of 1016.7 mA h g 1 at 100 mA g 1 after 100 cycles, and excellent high rate stability which shows impressive reversible capacity of 698.4 mA h g 1 at 1000 mA g 1 after 300 cycles.
author_names: Dapeng Wu

Yixin Wang

Nana Ma

Wenchao Zhang

Danqi Wang

Zhiyong Gao

Fang Xu

Kai Jiang
title: Single crystal like ZnO mesoporous spheres derived from metal organic framework delivering high electron mobility for enhanced energy conversion and storage performances
venue: Electrochimica Acta
year: 2019

abstract: A facile low temperature synthetic method of growing semiconductor mesoporous single crystal of anatase TiO2 directly on FTO substrate was developed. The templated hydrothermal synthesis approach was employed to make mesoporous single crystal TiO2 that contains pores tens to hundreds of nanometres in size under low temperature, which opens a potential way to produce useful functional thin film photoanodes by one pot approach for fabricating cheap and highly efficient optoelectronic devices. This method is based on seeded nucleation and growth inside a pre formed mesoporous silica film template immersed in diluted precursor solution. The electrochemical characterizations showed that the directly grown mesoporous single crystal thin film on FTO substrate has substantially higher conductivity and electron mobility than conventionally deposited TiO2 thin films by printing techniques. Hence, using the as synthesized mesoporous single crystal thin film baking at 150 degrees C as photoanodes, an encouraging 5.83% solar to electricity conversion efficiency was achieved. It is expected that the developed mesoporous single crystals on FTO substrate may find broader applications in many different technologies. This generic synthetic strategy extends the possibility of mesoporous single crystal films directly growing to a range of substrates. Moreover, this approach could work at lower temperatures below 150 degrees C, which could considerably minimize the environmental impact and production costs of high performance mesoporous materials. (C) 2015 Elsevier Ltd. All rights reserved.
author_names: Hua Yu

Lianzhou Wang

Matthew Simon Dargusch
title: Low temperature templated synthesis of porous TiO2 single crystals for solar cell applications
year: 2016

abstract: Single crystalline perovskite solar cells (PSC) are promising for their inherent stability due to the absence of grain boundaries. While the development of single crystals of perovskite with enhanced optoelectronic properties is known, studies on the growth, device performance and understanding of the intrinsic stability of single crystalline perovskite thin film solar cell devices fabricated on electron selective contacts are scarcely explored. In this work, we examine the impact of mesoporous TiO2 (m TiO2) and planar TiO2 (p TiO2) on the growth of single crystalline methyl ammonium lead iodide (SC MAPbI3) film, PSC device performance and film stability under harsh weather conditions (T 85 degC and RH 85% Self grown SC MAPbI3 films are developed on m TiO2 and p TiO2 by inverse temperature crystallization under ambient conditions without the need for sophisticated glove box processing. The best device with m TiO2 as an electron transport layer showed a promising power conversion efficiency of 3.2% on an active area of 0.3 cm2 in hole transport material free configuration, whereas, only 0.7% was achieved for the films developed on p TiO2. Complete conversion of precursor to perovskite phase and better surface coverage of the film leading to enhanced absorption and reduced defects of single crystalline perovskite on m TiO2 compared to its p TiO2 leads to this large difference in efficiency. Mesoporous device retained more than 70% of its initial performance when stored at 30 degC under dark for more than 5000 h at 50% RH; while the planar device degraded after 1500 h. Thermal and moisture endurance of SC MAPbI3 films are investigated by subjecting them to temperatures ranging from 35 degC to 85 degC at a constant relative humidity (RH) of 85% X ray diffraction studies show that the SC MAPbI3 films are stable even at 85 degC and 85% RH, with only slight detection (30 35% of PbI2 at these conditions. This study highlights the superior stability of SC MAPbI3 films which paves way for further studies on improving the stability and performance of the ambient processed PSCs.
author_names: Ramya Krishna Battula

Ganapathy Veerappan

Puttaiah Bhyrappa

C Sudakar

Easwaramoorthi Ramasamy
title: Stability of MAPbI3 perovskite grown on planar and mesoporous electron selective contact by inverse temperature crystallization
year: 2020

abstract: Organic inorganic hybrid perovskite solar cells (PSCs) employing a mesoporous metal oxide scaffold are now at the forefront of solution processed photovoltaic cells, yielding a power conversion efficiency exceeding 23% However, processing temperatures of up to 450 degC are typically required to sinter mesoporous metal oxide scaffolds, which hinders the fabrication of low cost and flexible devices. Moreover, these metal oxide scaffolds usually suffer from high charge carrier recombination rates and inherent UV instability. In this paper, we develop for the first time an organic scaffold architecture, which consists of room temperature processed C60 single crystalline nanoparticles (C60 NPs) serving as an electron selective contact covering on C60 compact films (c C60) C60 NPs act as a three dimensional framework to support perovskite crystals, enabling them to cover the substrate more uniformly and thus demonstrating an advantage over planar heterojunction PSCs. Furthermore, the higher electron mobility of C60 NPs compared with commonly used TiO2 enhances the charge transfer from the perovskite to electron transport layers and reduces charge carrier accumulation at the interface, demonstrating the advantage of an organic scaffold over inorganic metal oxides for mesoporous scaffold PSCs. A power conversion efficiency (PCE) of 19.45% was obtained in organic scaffold MAPbI3 based perovskite solar cells (OPSCs) outperforming standard reference devices based on a TiO2 mesoporous scaffold (maximum PCE 17.07% Furthermore, the high UV stability of C60 NPs enables the realisation of ultra stable OPSCs stressed under ambient conditions and working under both UV and full sun illumination. Moreover, the devices can be easily processed at low temperatures, providing an efficient method for the large scale production of flexible PSCs. These flexible PSCs show remarkable performance with an excellent PCE of 17.28% which is among the highest values reported for MAPbI3 based flexible PSCs to date. This work reveals that organic nanostructures as n type charge collection layers are ideal replacements for inorganic mesoporous scaffolds as they achieve remarkably high efficiency and long term operational stability in both rigid and flexible perovskite solar cells.
author_names: Xiaoming Zhao

Lixian Tian

Tianjun Liu

Hongli Liu

Shirong Wang

Xianggao Li

Oliver Fenwick

Shengbin Lei

Wenping Hu
title: Room temperature processed fullerene single crystalline nanoparticles for high performance flexible perovskite photovoltaics
year: 2019

abstract: Abstract Morphological and crystalline control over hybrid organic inorganic perovskite films is pivotal for efficient photovoltaic (PV) performance devices. Yet, this remains very challenging for solution processed perovskite solar cells (PVSCs) especially mesoscopic PVSCs, due to the complicated crystallization kinetics of hybrid semiconductor materials within dynamic spin coating and post annealing. In this work, colloidal Ge nanoparticles (NPs) were added onto a mesoporous TiO2 (m TiO2) electron transporting layer (ETL) to regulate perovskite crystal growth. Systematic investigation and optimization disclose that incorporation of an appropriate ratio of Ge NPs onto the m TiO2 ETL can simultaneously increase the size of the CH3NH3PbI3 crystals, decrease the number of the grain boundaries and promote the interfacial properties of perovskite/m TiO2. The related mechanisms are clarified through detailed morphology and crystal structure analyses. The electron mobility of the perovskite absorber, determined using the space charge limited current (SCLC) method, was increased by over 5 times when an optimized amount of Ge NPs were employed. Average power conversion efficiency (PCE) of 18.59% was achieved from 16 cells and the best PCE of 19.6% was attained via the addition of the optimized amount of Ge NPs. We study the fundamentals of optics and physics behind the PVSC device based on the high refractive index Ge NPs. This work offers an innovative scenario to enhance the performance of perovskite based optoelectronics by employing optically stable, chemically inert, low cost and green semiconductor NPs.
author_names: Chenxi Zhang

Zaifeng Li

Xueshuang Deng

Bing Yan

Zengbo Wang

Xiaohong Chen

Zhuo Sun

Sumei Huang
title: Enhancing photovoltaic performance of perovskite solar cells utilizing germanium nanoparticles
venue: Solar Energy
year: 2019

abstract: From the last few decades, organic semiconductors based electronic and optoelectronic devices have been the area of intense research.Organic semiconductors have gained remarkable importance in electronic and optoelectronic industry due to conjugated structure, low cost production, mechanical flexibility, ease of device fabrication and environmental friendly processing.In the research work reported in this dissertation, electronic, optoelectronic and amplified spontaneous emission (ASE) studies are carried out on (i) junction diodes using n type organic semiconductors, (ii) sensors fabricated using organic semiconductors and organic inorganic nanocomposites, and (iii) newly synthesized single crystal oligothiophene, respectively.The organic n type semiconductors N Butyl N' (6 hydroxy hexyl) perylene 3,4,9,10 tetracarboxylic acid diimide (N BuHHPDI) and perylene 3,4,9,10 tetra carboxylic acid di anhydride (PTCDA) have been synthesized and employed for their potential applications in organic devices such as Schottky barrier junction (SBJ) heterojunction (HJ) and organic multifunctional sensors.The fabricated rectifying junctions, i.e. Schottky junction and heterojunction, are characterized by conventional current voltage (I V) method at ambient atmospheric condition at in dark. Different junction factors i.e. turn on voltage (Vt) ideality factor/quality factor (n) rectification ratio (RR) barrier height (phb) reverse saturation current (I0) series resistance and shunt resistance are determined from the I V curves. Other two well known characterization techniques, Norde's technique and Cheungs' functions, are applied to measure the aforementioned parameters of the diode.The parameters extracted by these different characterization methods are compared and found in good agreement with each other.To understand the temperature dependence of the heterojunction device parameters, the I V properties of the heterojunction are studied at various temperatures from 300 K to 330 K.This has been observed that with the increase in temperature the ideality factor, turn on voltage and series resistance of the junction are significantly decreased. While the reverse saturation current and rectification ratios are increased.The morphological study of the thin films of N BuHHPDI and PTCDA deposited on quartz glass has been carried out by scanning electron microscope (SEM) and atomic force microscope (AFM) Size of the grain, shape, orientation and average surface roughness of the thermally deposited films has been measured from the microscopy.Energy dispersive spectroscopy (EDX) has been done for these samples to confirm the composition of these newly synthesized organic materials.To measure the optical band gap of these materials, ultra violet and visible (UV Vis) spectroscopy has been performed. The N BuHHPDI is insoluble in water and possesses excellent hydrophobic properties.This hydrophobic property makes these materials more distinctive candidates for humidity sensing applications as compared to other water soluble organic materials.The high sublimation temperature (700 K) is another convincing characteristic of this class of materials for their potential application as a temperature sensor to monitor temperature at elevated levels.At the same time, the broad UV Vis spectrum and good absorption of light recommend perylenes equally useful for light sensing applications.Thus, taking advantages of these motivating properties, the potential of perylene has been explored for humidity, temperature and light sensing applications due to the possession of such interesting properties all together.To enhance the performance of the organic semiconductor based sensors, one way is to make the sensor at nanoscale and the other is to blend organic semiconductor with some functional nanoparticles/nanofibers.For this reason, an organic azo dye, methyl orange (MO) has been used as an active semiconducting matrix in which the TiO2 nanoparticles have been disapersed.The fabricated sensor response has been observed at different humidity andtemperature values. Fast recovery time and response time of the sensor has been achieved due to the introduction of TiO2 nanoparticles by taking advantage of large surface to volume ratio of the nanoparticles.Concerning photonic characteristics of organic polymers and small molecules, conjugated polymers based optically pumped lasers have been produced both from solution and thin films.However, significant hard work is being carried out on these conjugated molecules to enhance their carriers' mobility and to minimize the threshold energy required for lasing to develop electrically pumped polymer laser diodes. Such types of materials for lasers may ultimately compete with their inorganic counterparts in many ways such as inexpensive, low temperature and high throughput fabrication. One special type of these materials is single crystal oligomers which, in the last decade, have got incredible attention due to their interesting properties such as high charge carriers' mobility, chemically adjustable wavelengths, large photoluminescence quantum efficiency (PLQE) large stimulated emission cross sections and as a high optical gain media for their prospective uses in solid state lasers and broadband amplifiers.The amplified spontaneous emission (ASE) optical gain and PLQE properties of a newly synthesized single crystal oligothiophene 5, 5' diphenyl 2, 2':5' 2':5' 2':5' 2':5' 2' sexithiophene (P6T) are reported. This oligomer crystal has been grown on glass substrate in a dimension of 5mm x 2mm with 10 mm thickness, by Prof. Shu Hotta, Kyoto Institute of Technology, Japan and its photonic properties have been studied at Cavendish Lab, Cambridge, UK.
author_names: Muhammad Tahir
title: Fabrication And Study of Organic Electronic And Optoelectronic Devices
year: 2014

abstract: A low temperature synthesis has been developed to make single crystals of titanium dioxide that contain pores tens to hundreds of nanometres in size. This opens the way to cheap, highly efficient optoelectronic devices. See Letter p.215 Mesoporous semiconductors and ceramics have large surface areas that can be exploited in high performance solar cells, as photocatalysts and in batteries. This paper describes a low temperature (below 150 degC) general synthetic method of growing micrometre sized semiconductor mesoporous single crystals of a form of titanium dioxide (TiO2) known as anatase, based on seeded nucleation and growth inside a mesoporous template immersed in a dilute reaction solution. The authors demonstrate that both isolated crystals and ensembles incorporated into films exhibit dramatically higher conductivities and electron mobilities than nanocrystalline TiO2. Dye sensitized solar cells made from these materials demonstrate 7.3% efficiency, the highest value so far reported using low temperature processing. The synthesis method should be generally applicable to other functional ceramics and semiconductors.
author_names: Caterina Ducati
title: Materials science: Porosity in a single crystal
venue: Nature
year: 2013

abstract: AbstractOwing to the electron scattering at the surface, the grain boundaries, and the defects of titanium dioxide (TiO2) nanoparticles (NPs) the electron diffusion length in the mesoporous TiO2 layer is shorter than that of TiO2 bulk single crystal, leading to a significantly increased charge recombination in dye sensitized solar cells (DSSCs) herein TiO2 photoanode sandwiching a layer of high mobility indium tin oxide (ITO) granular film to form a TiO2/ITO/TiO2 (TIT) photoanode. A large number of ITO NPs would penetrate deep into the mesoporous TiO2 bottom layer to form the interconnected network, which can be served as high speed electron transport channels, thereby enhancing the electron transfer and collection abilities. Compared with the reference device assembled with TiO2/TiO2 (TT) photoanode, an increase of 14.78% in power conversion efficiency (PCE) was obtained for the optimized TIT device (8.23 vs 7.17% which can be ascribed to the synergistic effects of faster electron transport and less charge recombination. Moreover, the electron transfer ability of TIT layer was also superior to TiO2 ITO composite photoanode, in which ITO NPs were uniformly dispersed in the TiO2 mesoporous layer. Overall, this method paves a facile and effective way to improve the photovoltaic performance for highly efficient DSSCs of practical significance. Graphical abstractThe interconnected transport channel consisting of the high mobility ITO interlayer enhances the electron transfer and collection abilities.
author_names: Haijun Chen

Tao Liu

Bing Wang

Zheting Liu

Yingxiang Li

Qiang Zhao

Ning Wang

Hongcai He

Hu Liu

Zhanhu Guo
title: Highly efficient charge collection in dye sensitized solar cells based on nanocomposite photoanode filled with indium tin oxide interlayer
venue: Advanced Composites and Hybrid Materials
year: 2018