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oeic on GaAs substrate
Published in G B Stringfellow, Gallium Arsenide and Related Compounds 1991, 2020
K. Goto, E. Ishimura, T. Shimura, M. Miyashita, Y. Mihashi, T. Shiba, Y. Okura, E. Omura, H. Kumabe
The fundamental efficiency limit of a conventional solar cell can be appreciated from Fig. 1a. If light with energy Eγ greater than the band-gap Eg is absorbed within a diffusion length of the p-n junction the carriers are separated by the built-in field, producing a current. The smaller the band-gap the larger the absorption and the bigger the output current. However, at room temperature, carriers rapidly thermalise to the band edge as a result of phonon interactions. The higher the band-gap the less this thermalisation loss and the higher the output voltage V. In a conventional solar cell the power conversion efficiency is therefore a compromise between the greater absorption available with a narrow band-gap and the greater output voltage achieved with a wide band-gap.
Multi-layer Graded Bandgap Solar Cells
Published in I. M. Dharmadasa, Advances in Thin-Film Solar Cells, 2018
This chapter has been devoted to presenting the advances made with a new device structure for PV solar cells. Its performance has been experimentally explored usinga well-researched GaAs/AlGaAs system. Thermalisation losses have been minimised using a graded bandgap multi-layer solar cell structure. By starting with a large bandgap material in the front and a gradual reduction of the bandgap towards the back of the solar cell, a major part of the solar spectrum can be absorbed while reducing thermalisation losses. This approach has a cooling effect for the solar cell with effective absorption of the major part of the solar spectrum and the creation of enhanced charge carriers.
Potential Applications
Published in Satyendra Mishra, Dharmesh Hansora, Graphene Nanomaterials, 2017
Satyendra Mishra, Dharmesh Hansora
A multilayer structure solar cell (see Fig. 4.23) can be envisaged with graphene and QDs to achieve total light absorption, thus higher efficiency. Another option is a multilayer structure heterojunction based on QDs (MoS2, WS2, CdS, PbS, ZnS, etc.) alternating with graphene conductive layers, or coupling a standard DSSC with a graphene/MoS2 (or WS2) tandem solar cell. The aim is to overcome the η of state-of-the-art solar cells extending it beyond the Shockley-Queisser limit (i.e. the maximum theoretical efficiency of a p-n junction solar cell) by using multiple sub-cells in a tandem device. Ideally, the sub-cells would be connected optically and electrically and stacked in band gap decreasing order. This configuration shifts the absorption onset of the complete device towards longer wavelengths. In addition, high-energy photons are converted more efficiently since thermalisation losses of the generated e-h pairs are reduced with the graded band gap structure. For example, in a series-connected double-junction device, the ideal optical band gaps are ~1.6–1.7 eV for the top cell and ~1.0–1.1 eV for the bottom cell, which extends the efficiency limit to ~45% [21, 415]. Another possibility is to assemble hybrid graphene/nanodiamonds [416, 417] motivated by the properties of both materials, and possible interactions between sp2 and sp3 carbon [418]. The <111> diamond surface could form an ideal interface for heteroepitaxial graphene, with ~2% mismatch. The armchair diamond rings on the <111> surface can be interfaced to the six-membered C rings of graphene. There are several impacting interests in these interfaces. Undoped nanodiamond could serve as gate insulator. A controllable functionalisation of nanodiamond may be used to tune graphene’s (μ and work function other than the optical properties. This might be achieved by coupling graphene to nanodiamond using organic chemistry routes via linkers with functional properties. In these solar cells, conductive B-doped nanodiamond would serve as anode, while graphene would be the cathode. If donor-acceptor organic dyes are used for such interfacing, the proposed full carbon structure would have effective charge transfer from the highest occupied molecular orbital (HOMO) of the organic dye to the diamond valence band, and in a reversed process on the graphene/lowest unoccupied molecular orbital (LUMO) side. Another approach relies on the use of chemically synthesised GNRs and/or GQD sensitisers in solar cells. GQDs have been synthesised with molar extinction coefficients (~1 × 105 M−1cm−1 [419], one order of magnitude larger than inorganic dyes (e.g. ruthenium complexes), 956 commonly used in DSSCs) and absorption edge beyond 900 nm [419].
Understanding the temperatures of H3 + and H2 in diffuse interstellar sightlines
Published in Molecular Physics, 2023
Jacques Le Bourlot, Evelyne Roueff, Franck Le Petit, Florian Kehrein, Annika Oetjens, Holger Kreckel
The demonstration starts from a full treatment of the differential state equations, including all possible processes, i.e. collisional and radiative transitions as well as chemical state-to-state formation and destruction reactions. Solving these equations, the next section (4.1) will show that we can indeed recover a value for the excitation temperature that is systematically below the gas kinetic temperature, similar to observational results. The next sub-section explores how sensitive these equations are to the number of levels included in the computation. This allows to understand why at least 5 levels must be included for quantitative results. It also shows that the range is much less sensitive to the number of levels included. By restricting our analysis to this temperature range, we can derive a qualitative analytical approximation with only two levels (Section 4.3). The resulting expression shows that selective formation of p- by p- followed by incomplete thermalisation is responsible for the deviation from thermal equilibrium.
Thermal modelling, performance analysis and exergy study of a concentrated semi-transparent photovoltaic-thermoelectric generator (CSPV-TEG) hybrid power generation system
Published in International Journal of Sustainable Energy, 2021
Abhishek Tiwari, Shruti Aggarwal
In the time span ranging from 1 pm to 5 pm, the input solar energy I(t) steeply decreases, as shown in Figure 6, and the temperature of the solar cell also decreases due to the decrease in the amount of waste heat generated by thermalisation loss and transmission loss. The generation of useful electrical energy in the form of PPV also decreases, but it does not decrease as steeply as I(t). As a result, both ηSC and ηPV increase in this time span for all the six cases under consideration. The values of ηSC and ηPV also depend upon C and N. For a fixed value of N, a higher value of C causes a significant increase in TSC, which decreases both ηSC and ηPV. As a result, ηPV and ηsc attain lower values for all those cases where C = 2 and comparatively higher values for all those cases where C = 1. This is shown in Figure 9 where ηPV value for C = 1 N = 62 case, C = 1 N = 127 case and C = 1 N = 200 case is higher than the ηPV value for C = 2 N = 62 case, C = 2 N = 127 case and C = 2 N = 200, respectively. The same explanation holds for hourly variation of ηSC shown in Figure 8 for the same time span.
Formation of argon cluster with proton seeding
Published in Molecular Physics, 2020
O. C. F. Brown, D. Vrinceanu, V. Kharchenko, H. R. Sadeghpour
We are interested in the short-time dynamics of Ar and Ar–p cluster nucleations. Experimentally, the proton seeding could be implemented by selective laser ionisation of H atoms in the Ar and H gas mixture. Energies of photo-electrons can be significantly larger than the bath gas temperature. Energy relaxation of electrons occurs mostly in collision with the Ar atoms and the electron plasma thermalisation requires significantly more time than the characteristic time of cluster formation. For example, electrons with energies around 11.5 eV can form the long-living metastable ions Ar(3p4s4p) with the lifetime ∼260–300 ns [44]. This time is much larger than a time of ∼10 ns required for the production of critical clusters. Energetic electrons do not play a significant role in Debye screening and, aside from providing the plasma neutrality, they are not material to the simulations.