Xiao Lixin

Electronic properties of graphene nanoribbon doped by boron/nitrogen pair: a first-principles study

By using the first-principles calculations, the electronic properties of graphene nanoribbon (GNR) doped by boron/nitrogen (B/N) bonded pair are investigated. It is found that B/N bonded pair tends to be doped at the edges of GNR and B/N pair doping in GNR is easier to carry out than single B doping and unbonded B/N co-doping in GNR. The electronic structure of GNR doped by B/N pair is very sensitive to doping site besides the ribbon width and chirality. Moreover, B/N pair doping can selectively adjust the energy gap of armchair GNR and can induce the semimetal?semiconductor transmission for zigzag GNR. This fact may lead to a possible method for energy band engineering of GNRs and benefit the design of graphene electronic device.

Progress of efficiency enhancement of organic light-emitting diodes via surface plasmon

The surface plasmon polariton (SPP), exists at the interface of metal and media, where the optical field and the free electron can interact with each other and results in an oscillations of collective electrons. On one hand, a localized surface plasmon (LSP) can be formed on the surface of metal nanoparticles, and then the quantum yield of fluorescent molecules near the surface metal can be enhanced by the LSP. Therefore, many efforts have been paid to add metal nanoparticles into organic light-emitting diode (OLED) to improve its performance. On the other hand, in a conventional device, SPP can’t emit light to free space because the wave vector of it doesn’t match to that of free light, and then dissipates as heat. By changing the morphology of the metal surface, such as grating structure, the energy of SPP can be coupled into free light field, and the external quantum efficiency of device can be enhanced. It has been widely concerned on SPP to enhance the efficiency of OLED. This article reviews the progress on the following two aspects. Firstly, enhancing the rate of radiative transition of fluorescent molecules by using LSP of metal nanoparticles, which can enhance the internal quantum efficiency of organic light-emitting diodes; Secondly, emiting a light via matching the wave vector of SPP to that of free light with a grating structure of periodicity or unperiodicity, which can enhance the external quantum efficiency of OLED.

Aggregation Induced Fluorescence Blue-Shift of Zinc Bis(8-hydroxyquinoline) Modified with Cholesteryl

Aggregation induced fluorescence blue-shift of the newly synthesized zinc bis(8-hydroxyquinoline) modified with cholesteryl (Zn(ChQ)2) is studied by static and picosecond transient emission spectroscopy.Fast solvent-induced charge transfer is found when Zn(ChQ)2 is dissolved in polar solvents.The twisted intramolecular charge transfer (TICT) state is formed as new emission state.Its emission spectra of Zn(ChQ)2 in aggregation form (film state) are blue-shifted compared to those in polar solvents.Steric hindrance induced weakened intermolecular interaction in aggregations lead to blue-shifted emission and enhanced quantum efficiency.Intermolecular energy transfer is found in solid film and independent on emission wavelength.

Ultrafast Photophysics of Star-Like Molecules with Benzene and Triazine Core

Static and transient spectroscopic characters of newly synthesized start-like molecules, 1,3,5-tri(10-butyl-3-propenyl-10H-phenothiazine)-benzene (TP3B) and 2,4,6-tri(10-butyl-3-propenyl-10H-phenothiazine)-[1,3,5]triazine (TP3T), are studied using static, picosecond fluorescence and femtosecond transient absorption spectroscopy. The results show that when the benzene group is in the center, a large conjugation system is formed, while a fast electron-transfer process happens when the center group is triazine.

Large-area thin film deposition technologies for fabricating hybrid perovskite solar cells

Organic-inorganic hybrid perovskite solar cells have attracted tremendous research interests due to their amazing light to electric power conversion efficiencies (PCEs). In the past four years, the PCE of perovskite solar cells has significantly increased up to 22.1%, which outperforms several other types of third-generation solar cells and becomes the most promising candidate to compete with the traditional silicon-based solar cells. This result is mainly owing to some excellent properties of the hybrid perovskite active layer, such as a high absorption coefficient, an appropriate band gap and a long carrier diffusion length. Nevertheless, most of the reported high efficiencies were only achieved with very small active areas in the range of 0.03 to 0.2cm2, which is likely to cause measurement errors. What is worse, the material utilization ratio is only 1% during film deposition, hindering the industrial production of perovskite solar cells in the future. Therefore, a large-scale production process has become a big challenge to realize the purpose of commercial applications. To date, the best certified PCE of 19.6% has been obtained with an active area exceeding 1cm2. The most important aspect is fabricating large-area uniform, pinhole-free and large crystal grain perovskite thin films for scaling up high PCE perovskite solar cells. To realize the purpose of large-area, high-quality perovskite film fabrication, a range of thin film fabrication techniques have been proposed, including spin-coating, vacuum flash-assisted solution process (VASP), doctor blading, slot-die coating, inkjet printing, spray coating, vapor assisted deposition and soft-cover deposition. This review aims at giving an overview of these thin film deposition techniques for the processing of perovskite thin film fabrication. By comparing the film quality and material utilization ratio corresponding to different film deposition methods, the studies on perovskite thin film fabrication techniques are summarized. Among these techniques, spin-coating has been widely used in laboratory for perovskite film fabrication, but the material utilization ratio is usually less than 1%, hindering the fabrication of perovskite film with large-area. Spin-coating combined with VASP exhibits an amazing result for high-quality perovskite film fabrication, but it still has a low material utilization ratio in spin-coating process. Other techniques, like doctor blading, slot-die coating and inkjet printing are suitable for large-area perovskite film fabrication with high material utilization ratio. Spray coating and soft-cover deposition also have shown great potential for large-area perovskite film fabrication. The PCEs of perovskite solar cells have reached 13% and 17% with an active area exceeding 1cm2, respectively. Particularly, a high-quality perovskite film with a large-area of 51cm2 was obtained by soft-cover deposition, which made this technique more promising for the development of perovskite solar cells in the future. Based on this review, we suggest that VASP is a suitable technique for depositing high-quality large-area perovskite film. It would be a promising technique to combine VSAP with other techniques, such as doctor blading, inkjet printing, etc., to enhance material utilization ratio for large-scale perovskite solar cells. In addition, some simpler and lower-cost techniques should be developed for the fabrication of perovskite solar cells in the future.

The analysis of the efficiency of solarcells

Under the circumstances of the increasing depletion of fossil fuels, renewable energy, especially solar energy, is becoming more and more important. Thus, the methods of exploring solar energy are diverse and the energy conversion efficiency keeps rising while the cost keeps decreasing. Among all the methods, using solar cell is the main way to explore solar energy. Currently, solar cells can be divided into three main categories, crystalline silicon solar cells, thin film solar cells and novel solar cells. Crystalline silicon solar cells can also be divided into monocrystalline silicon solar cell and polycrystalline silicon solar cell. These two kinds of solar cells are the most common solar cells in our daily life. The efficiency of monocrystalline silicon solar cell is already pretty high reaching 25% while polycrystalline silicon solar cell reaches 21.3%. The stability of monocrystalline silicon solar is also better than that of polycrystalline silicon solar cell. The only fly in the ointment is that the cost of monocrystalline silicon solar is a little bit higher than polycrystalline silicon solar cell which makes monocrystalline silicon solar not optimal enough. Thin film solar cell includes amorphous silicon solar cells and multi-compounds solar cells. The transformation of solar cells from solid panel to thin film is one of the most significant breakthroughs of the second generation solar cell. The amorphous silicon solar cell becomes much cheaper than both monocrystalline silicon and polycrystalline silicon solar cells. But its drawback is obvious, its efficiency only reaches 13.6% which certainly needs to be improved. As for semiconductor compounds solar cells, there are made by various semiconductor materials. Major semiconductor compound solar cells contain chemical materials such as CdTe, CuInSe2(CIS), CuInSe2 doped Ga(CIGS), GaAs, InP, and multi-junction solar cell, etc. Materials like CdTe and CIGS can surely lower the cost of solar cells and their efficiencies are pretty high reaching 21.5% and 22.3%, respectively. But Cd is a toxic element while In and Se are rare elements, their reserves are limited. Materials like GaAs and InP are much more expensive comparing to others, but their efficiencies are pretty satisfying reaching 28.8% and 22.6%, respectively. More importantly, they have rather high radiation tolerance, especially InP solar cell has the best radiation tolerance among all kinds of solar cells. Thus, despite their high costs, they can still be used in many situations such as space station. As for multi-junction solar cell, the most prominent feature of it is the high efficiency. Solar cells with two junctions, three junctions and four junctions have reached the efficiencies of 31.6%, 37.9% and 38.8%. Obviously, multi-junction solar cells are the best choice to improve energy conversion efficiency. The novel solar cell consists of organic solar cells, dye-sensitized solar cells, quantum dot solar cells and hybrid perovskite solar cells. Among all these third generation solar cells, perovskite solar cell is the most promising one due to its superior properties and rapid improvement. Its efficiency has already reached 21% in only a few years. But more work needs to be done to improve its properties such as its stability and currently perovskite solar cell still contains lead which is toxic and may need to be replaced. This paper starts from analyzing the theoretical efficiency of solar cells, then compares those theoretical efficiencies with experimental efficiencies to present the expectation of different kinds of solar cells.