Papers by Keyword: Recombination

Abstract: We demonstrated the construction and performance of dye-sensitized solar cells (DSCs) based on nanoparticles of TiO₂ coated with thin shells of MgO by simple solution growth technique. The XRD patterns confirm the presence of both TiO₂ and MgO in the core-shell structure. The effect of varied shell thickness on the photovoltaic performance of the core-shell structured electrode is also investigated. We found that MgO shells of all thicknesses perform as barriers that improve open-circuit voltage (Voc) of the DSCs only at the expense of a larger decrease in short-circuit current density (Jsc). The energy conversion efficiency was greatly dependent on the thickness of MgO on TiO₂ film, and the highest efficiency of 4.1% was achieved at the optimum MgO shell layer.

Abstract: Silicon nanocrystals (Si NCs) are a promising candidate for the top cell of an all-Si tandem solar cell with a band gap from 1.3-1.7 eV, tuneable by adjusting NC size. They are readily produced within a Si-based dielectric matrix by precipitation from the Si excess in multilayers of alternating stoichiometric and silicon-rich layers. Here we examined the luminescence and transport of Si NCs embedded in SiC. We observed luminescence that redshifts from 2.0 to 1.5 eV with increasing nominal NC size. Upon further investigation, we found that this redshift is to a large extent due to Fabry-Pérot interference. Correction for this effect allows an analysis of the spectrum emitted from within the sample. We also produced p-i-n solar cells and found that the observed I-V curves under illumination could be well-fitted by typical thin-film solar cell models including finite series and parallel resistances, and a voltage-dependent current collection function. A minority carrier mobility-lifetime product on the order of 10^-10 cm²/V was deduced, and a maximum open-circuit voltage of 370 mV achieved.

Abstract: In this paper we developed a recombination model for the steady state photoconductivity (SSP) with the assumption that the correlated dangling bond states (DB) act as the essential recombination centres and the electron recombination proceeds by tunneling from the conduction band tail states (TS) for n-type a-Si:H. The modeled temperature dependence of the SSP presents the main measured features, particularly the small activation energy and the thermal quenching.

Abstract: Electronic device that subjected to various effects by radiations can cause small interferences such as noises in the circuit. These effects are especially critical in operating environment such as outer space, where radiation comes in stronger and more frequent. In this research, analytical study on the effects of ionizing radiation induced by ⁶⁰Co gamma (γ) rays in bipolar junction transistor (BJT) devices had been performed. It was found that the high energy of the radiation allows more valence electrons to be excited to the conduction band in the BJT. This leads to the production of a large number of excited atoms and increases the holes in the valence band. The increase of holes in the base region due to trapping will increase the probability of recombination and reducing the number of electrons that reaches the collector region. This ionizing radiation effect was found to arouse either a permanent or temporarily damage in the devices depending on their current drives and total dose absorbed.

Abstract: The V-doped TiO2 nanoparticles were successfully prepared by sol-gel method and characterized by X-ray diffraction (XRD), UV-vis spectroscopy and photoluminescence (PL) spectroscopy respectively. It is found that doping V can shift the absorption edge to the visible light region and decrease the recombination of photo-induced electron-hole pairs. Then the photo-absorption and photocatalytic activity were greatly improved. The optimal doping concentration is 0.5% due to synergetic effect of the recombination of electron-hole pairs and adsorption of dyes molecules at the surface of samples.

Abstract: We applied an effective medium model for a computational study and investigated a recombination mechanism in a P3HT:PCBM bulk heterojunction (BHJ) organic solar cells where the main assumption is the p-n nanostructure is treated as one single effective semiconductor layer, and parameters in this configuration are fed into a standard solar cell device simulator, called a Solar Cell Capacitance Simulator (SCAPS). Using SCAPS, the electrical performances of organic solar cells and the intensity-dependent current density -voltage (J-V) were simulated and compared with the actual experimental result. The results show that they are in good agreement with each other and monomolecular recombination mechanism is the dominant mechanism in the BHJ organic solar cells.

Abstract: Single-crystal TiO₂ nanorod film was synthesized directly on FTO substrates with various lengths by changing the hydrothermal growth parameters including growth time and growth temperature. The obtained nanorod arrays were incorporated in organic solar cells as buffer layer instead of PEDOT: PSS. Results showed that devices assembled with TiO₂ nanorods film of 200 nm in length exhibited a lower open-circuit voltage but a significantly higher short-circuit current density compared to those of normal FTO/PEDOT: PSS/P3HT: PCBM/Al structure with a comparable active layer thickness. Overall the power conversion efficiency was boosted by two-fold. Electrochemical impedance spectroscopy (EIS) analyses revealed that the improvement in the photovoltaic performance was induced by the inhibited recombination and consequently enhanced electron lifetime.

Abstract: Recent advances in preparing n-type 4H-SiC with long carrier lifetimes have greatly enhanced the possibility of realizing commercially available, very high voltage and high power solid state switching diodes. For the range > several kV, vertical bipolar structures are required with drift layers exhibiting carrier lifetimes ≥ several µsec. Recently, low-doped epilayers with carrier lifetimes in excess of this have been demonstrated, thus approaching a goal that has been pursued for over a decade. Historically, the short lifetimes in early epitaxial layers (a few hundred nsec) were eventually identified with the V_c-related Z_1/2 lifetime killer. Current strategies to minimize this defect are an essential ingredient in the procedure for obtaining long-lifetime material. In order to optimize the attainable lifetimes, it has been shown that in addition to low Z_1/2 levels, very thick layers are required to minimize the effects of recombination in the substrate and surface passivation is also necessary to minimize surface recombination (S < 1000 cm/sec).

Abstract: Evolution of a molybdenum system containing self-interstitials and vacancies was studied by molecular dynamics simulation using a new molybdenum interatomic potential. The potential was parameterized by using formation and migration energies of the defects. Clustering and annihilation of the defects were investigated in terms of the defect concentration changes during the calculation. The rate constants were evaluated and compared with the diffusion coefficients. Also investigated was the influence of one-dimensional diffusion on kinetics, as well as the effects of temperature and defect concentrations on the reaction rates.

Abstract: Research and analyze the multi-thread schedule methods of the adjusted pressure casting control system deeply. Present an analysis method of related slice graphs based on the code slice and a theory of code subdivision based on the slice granularity and time slice. Then strictly divide the program of control system based on the time slice and obtain the strategies of event driven schedule and time slice schedule by analyzing the casting system. Subsequently, subdivide and recombine the multi-thread program slices based on the priority of the schedule strategies in control system. The control system was applied to the TYM-1 adjusted pressure casting system and the preferable effect is acquired.