Download or read book Luminescence and Transport Processes of Charge Carriers in the Gaxin XP GAAS Double Junction Tandem Solar Cells written by Zhuo Deng and published by Open Dissertation Press. This book was released on 2017-01-27 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Luminescence and transport processes of charge carriers in the GaxIn₁-xP/GaAs double-junction tandem solar cells" by Zhuo, Deng, 鄧卓, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Semiconductor multijunction solar cell is a cutting-edge photovoltaic technology aimed at developing a frontier solution to the clean energy demand and environmental problem. Due to the efficient photoabsorption and energy conversion in the visible and near-infrared spectral ranges of the solar spectrum, the multijunction solar cell structures have shown an unprecedented application potential by demonstrating a solar conversion efficiency of over 44 %. Among various multijunction solar cell structural designs, the GaxIn1-xP/GaAs double-junction tandem structure is considered as the most fundamental building block for developing the industry-standard triple- and even more junction photovoltaic cells with super high efficiency. Therefore, obtaining a better and more in-depth understanding of physical properties of the GaxIn1-xP/GaAs double-junction tandem device structure, especially some fundamental optoelectronic processes in the individual structural layer, including photoexcitation, transport and the mid-way recombination of charge carriers, is crucial for further improving the energy conversion efficiency. In this thesis, the mid-way radiative recombination, diffusion transport, localization mechanism, and photocurrent spectra of charge carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells grown on GaAs substrates with different misorientation angles were investigated in detail. Our main findings are summarized as below. Efficient radiative recombination of carriers in the GaxIn1-xP/GaAs double-junction tandem solar cell samples was demonstrated by using electroluminescence (EL) and photoluminescence (PL) techniques. The radiative recombination intensity was shown to be dependent on the intrinsic material-related parameters such as the doping concentration, growth thickness and the substrate misorientation angle both experimentally and theoretically. The radiative recombination was thus revealed to be an important loss channel of carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells. Super strong transverse diffusion of minority carriers in the top GaxIn1-xP subcell was found by the micro-EL image surveying. Theoretical simulation on the experimental data shows that the minority carrier diffusion length is as long as 93 μm at a forward bias of 2.75 V, which is 30 times longer than that of unbiased GaxIn1-xP epilayer. Origin of this super transverse diffusion was argued, and its influence on device performance was also discussed. Significant correlations of carrier localization and luminescence behaviors with the substrate misorientation angle in the top GaxIn1-xP subcells were unveiled by excitation intensity- and temperature-dependent PL. The large difference in potential energy profile of GaxIn1-xP layers, caused by the different degrees of atomic ordering, was argued to interpret the observed PL distinctions. Vertical transport and photoresponse mechanisms of charge carriers in the GaxIn1-xP/GaAs double-junction tandem solar cells were studied by temperature- and reverse bias-dependent photocurrent (PC) spectroscopy. Both the temperature and reverse bias were shown to have significant impact on the device photoresponse, in particular on the photoresponse due to the absorption of photons with energy above the bandgap of GaAs and GaxIn1-xP, namely the supra-bandgap photoresponse. A model was proposed

Download or read book Luminescence and Transport Processes of Charge Carriers in the GaxIn1 xP GaAs Double junction Tandem Solar Cells written by and published by . This book was released on 2014 with total page 238 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Spectroscopic Investigations of Transfer and Transport of Charge Carriers in the Donor Acceptor Network of Organic Solar Cells written by Helene Ahme and published by . This book was released on 2014-09-15 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Direct Observation of Carrier Transportation Process in InGaAs GaAs Multiple Quantum Wells Used for Solar Cells and Photodetectors Supported by the National Natural Science Foundation of China Under Grant Nos 11574362 61210014 and 11374340 and the Innovative Clean Energy Research and Application Program of Beijing Municipal Science and Technology Commission Under Grant No Z151100003515001 written by and published by . This book was released on 2016 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract : The resonant excitation is used to generate photo-excited carriers in quantum wells to observe the process of the carriers transportation by comparing the photoluminescence results between quantum wells with and without a p—n junction. It is observed directly in experiment that most of the photo-excited carriers in quantum wells with a p—n junction escape from quantum wells and form photocurrent rather than relax to the ground state of the quantum wells. The photo absorption coefficient of multiple quantum wells is also enhanced by a p—n junction. The results pave a novel way for solar cells and photodetectors making use of low-dimensional structure.

Download or read book Direct Imaging of Minority Charge Carrier Transport in Triple Junction Solar Cell Layers written by Ted Jonathan Mills and published by . This book was released on 2006 with total page 81 pages. Available in PDF, EPUB and Kindle. Book excerpt: An optical, contact-free method for measuring minority carrier diffusion lengths is developed and demonstrated for a range of semiconductor materials used in high efficiency triple junction solar cells. This method uses a Scanning Electron Microscope (SEM) coupled with an optical microscope. The diffusion lengths, combined with minority carrier lifetime measured via time-resolved photoluminescence, allow for the computation of minority charge carrier mobility. The technique uses images to extract diffusion length measurements from GaAs, InGaAs, and InGaP heterostructures at different SEM beam energies and probe currents. Excellent correlation between measurements shows the reproducibility of this technique. Diffusion lengths from 2-63 microns have been measured in a variety of GaAs, InGaAs, and InGaP samples. Effects of alloy ordering, doping, and lattice matching have been investigated. Several areas for further research are offered, including detailed radiation-damage mapping of solar cell layers. Further anisotropic studies of the solar cell layers are suggested to investigate the directional dependence of diffusion length within the InGaP heterostructures. Finally, new and emerging solar cell materials would benefit from this technique, allowing for the complete characterization of minority charge transport properties before growing an entire solar cell.

Download or read book GaInP GaAs Tandem Solar Cells with Highly Te and Mg doped GaAs Tunnel Junctions Grown by MBE Project Supported by the SINANO SONY Joint Program Grant No Y1AAQ11001 the National Natural Science Foundation of China Grant No 61274134 the USCB Start up Program Grant No 06105033 and the International Cooperation Projects of Suzhou City China Grant No SH201215 written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: We report a GaInP/GaAs tandem solar cell with a novel GaAs tunnel junction (TJ) with using tellurium (Te) and magnesium (Mg) as n- and p-type dopants via dual-filament low temperature effusion cells grown by molecular beam epitaxy (MBE) at low temperature. The test Te/Mg-doped GaAs TJ shows a peak current density of 21 A/cm 2 . The tandem solar cell by the Te/Mg TJ shows a short-circuit current density of 12 mA/cm 2, but a low open-circuit voltage range of 1.4 V∼1.71 V under AM1.5 illumination. The secondary ion mass spectroscopy (SIMS) analysis reveals that the Te doping is unexpectedly high and its doping profile extends to the Mg doping region, thus possibly resulting in a less abrupt junction with no tunneling carriers effectively. Furthermore, the tunneling interface shifts from the intended GaAs n ++ /p ++ junction to the AlGaInP/GaAs junction with a higher bandgap AlGaInP tunneling layers, thereby reducing the tunneling peak. The Te concentration of ∼ 2.5 × 10 20 in GaAs could cause a lattice strain of 10 −3 in magnitude and thus a surface roughening, which also negatively influences the subsequent growth of the top subcell and the GaAs contacting layers. The doping features of Te and Mg are discussed to understand the photovoltaic response of the studied tandem cell.

Download or read book Fundamental Studies of Charge Transport for Optoelectronic Processes written by Qinglong Jiang and published by . This book was released on 2015 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt: Charge transport at interfaces and in bulk phases governs the efficiency and performance of various heterojunction optoelectronic devices such as solar cells and electrochromic devices. In this dissertation, research on charge transport processes in two different optoelectronic devices (nanostructured heterojunction photovoltaic cells and electrochromic devices) is presented.

Download or read book Charge Transport and Recombination in Hybrid Organic inorganic Solar Cells written by Alexander Robert Pascoe and published by . This book was released on 2015 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hybrid organic-inorganic solar cells have been cited as a promising alternative to presently commercialised photovoltaic technologies. However, despite over 20 years of research into hybrid organic-inorganic solar technologies, there are still many unknowns concerning the physical operation of these devices. The two most successful technologies comprising the discipline of hybrid organic-inorganic solar cells are the dye-sensitised solar cell (DSSC) and the perovskite-based solar cell (PSC). This thesis reports on charge transport and recombination mechanisms occurring within DSSC and PSC devices.The first phase of this work examined the role of electron traps on charge recombination in DSSCs, and whether reports of trap state passivation were justified. Electrochemical impedance spectroscopy (EIS) and intensity-modulated photovoltage spectroscopy (IMVS) were used to characterise nanoparticle TiO2 films treated with an atomic layer deposited (ALD) coating. The application of a theoretical model to the experimental data was used to characterise the relative contributions of conductive states and trap states to the total recombination rate. The interpretation of these results indicated that the ALD surface treatment reduced recombination from conductive and trap states evenly, and did not selectively passivate surface traps.The second phase of this thesis explored the physical characteristics of DSSCs formed on flexible plastic substrates, as well as electron transport rates within nanostructured TiO2 beads. EIS, IMVS, intensity-modulated photocurrent spectroscopy (IMPS) and transient measurements revealed that the benchmark fabrication techniques of cold isostatic pressing (CIP) and nanoglue treatments resulted in electron diffusion lengths 3 - 4 times shorter than those produced via a high-temperature sintering step. Characterisation of charge transport kinetics within mesoporous TiO2 beads identified two effective diffusion rates: one pertaining to intra-bead diffusion, and the other to inter-bead connections.The third phase of this work entailed the characterisation of planar PSCs primarily through EIS. Impedance spectroscopy measurements of planar PSC devices revealed high-frequency and low-frequency features that exhibited different dependencies on the charge carrier concentration. Based on additional photoluminescence (PL) and transient measurements, as well as the formative work of previous studies, an equivalent circuit model was proposed to describe the impedance spectroscopic response of planar PSC devices.The final phase of this thesis aimed to characterise the differences in transport and recombination dynamics between planar and mesoscopic architectures. Time-resolved microwave conductivity (TRMC) and time-resolved PL measurements revealed higher charge mobilities and lower trap-mediated recombination dynamics in planar perovskite films compared to mesoscopic perovskite films. The consolidation of the best aspects of each architecture into a new PSC assembly was found to increase the overall power conversion efficiency. In an extension of this work, a different perovskite precursor solution was used to produce a textured, mesoscopic perovskite layer without the use of a thick nanoparticle scaffold. This textured morphology was capable of enhancing further the optical and charge separation properties of the device, resulting in a maximum power conversion efficiency of 16.3 %. The work undertaken in the aforementioned studies highlights how a deeper understanding of hybrid organic-inorganic solar cell physics can be used to further optimise the solar cell performance.