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Photovoltaics
Published in D. Yogi Goswami, Principles of Solar Engineering, 2023
The limits imposed on solar cells owing to band gap can be partially overcome by using multiple layers of solar cells stacked on top of each other, each layer with a band gap higher than the layer below it. For example (Figure 9.13), if the top layer is made from a cell of material A (band gap corresponding to λA), solar radiation with wavelengths less than λA would be absorbed to give an output equal to the hatched area A. The solar radiation with a wavelength greater than λA would pass through A and be converted by the bottom layer cell B (band gap corresponding to λB) to give an output equal to the hatched area B. The total output and therefore the efficiency of this tandem cell would be higher than the output and the efficiency of each single cell individually. The efficiency would increase with the number of layers. For this concept to work, each layer must be as thin as possible, which puts a very difficult if not an insurmountable constraint on crystalline and polycrystalline cells to be made multijunction. As a result, this concept is being investigated mainly for thin-film amorphous solar cells.
Multi-angular instrument for tower-based observations of canopy sun-induced chlorophyll fluorescence
Published in Instrumentation Science & Technology, 2020
Shuren Chou, Bin Chen, Jing M. Chen
The original spectra of the two spectrometers were interpolated to a resolution of 0.01 nm using the measurements at the nearest wavelength. Then, they were resampled to a resolution of 0.1 nm. Finally, the 3FLD method was used to calculate SIF values. For the O2-B band, 686.38 nm was used as the wavelength inside the O2 feature, and the shoulders were sampled at 686.98 and 687.88 nm, respectively (the left and right of the O2 feature). For the O2-A band, 759.54 nm was used as the wavelength inside the O2 feature, and the shoulders were sampled at 758.00 and 761.85 nm, respectively.
Dual-cavity spectrometer for monitoring broadband light extinction by atmospheric aerosols
Published in Aerosol Science and Technology, 2020
Aiswarya Saseendran, Susan Mathai, Shreya Joshi, Anoop Pakkattil, Tyler Capek, Gregory Kinney, Claudio Mazzoleni, Ravi Varma
For example, the changes in the fractional absorption of the O2 B-band was used to retrieve the aerosol extinction coefficient at a single wavelength (687 nm) (Suhail et al. 2019; Varma et al. 2013). In this study, the SC-BD-CEES covers a broad visible range from 420 to 540 nm. The optical instrumentation, aerosol generation and delivery, measurement methods, and calibration scheme are described in detail in the following sections.
The influences of lateral groups on 4-cyanobiphenyl-benzonitrile- based dimers
Published in Liquid Crystals, 2022
Srinatha M K, Ayesha Zeba, Anjali Ganjiwale, Ashwathanarayana Gowda, Gurumurthy Hegde, Mohamed Alaasar, G. Shanker
UV-visible absorption spectra were recorded for the dimers (X-Dn) as a function of concentration in dichloromethane (DCM). As an example, the electronic absorption of CN-D9 is shown in Figure 3, three distinct peaks are observed between 200 and 350 nm of B band, indicating the effect of polar substituents and the methylene spacer connecting two promesogenic units. The electron-withdrawing cyano group small in size provides excellent stability under UV irradiation. The position of cyano groups in phthalonitrile segment is vital for strong photophysical properties [63]. Three noticeable peaks in the B band at λ = 300, 265, 228 nm display the characteristics of hypsochromic shift (shorter wavelength) with increased intensity as variation in concentration. Further, on dilution these peaks break down into smaller ones and disappears at 3.125 × 10−6 M, indicating a decrease in the intermolecular interactions as a result of weak n – π* transition with no conjugation arising from cyano group. The absence of any Q-band is surprising inspite of having three – CN group in this dimer, which have greater tendency to induce the dipole–dipole interactions. The aggregation in the B-band results due to intermolecular interaction and found to be maximum around λ = 300 nm and peak size reduces further before disappearing below 220 nm. The peak intensity has the ratio of 1:0.7:0.85 and strong aggregation visible in the first peak and continues to disintegrate the aggregation size as visible in second and third peaks. Reminiscent aggregational behaviour observed for the F-D8 dimer of fluoro series, three distinct B-band peaks at λ = 300, 285, 250 nm (See ESI) but the H-Dn dimers display only two peaks (λ = 300, 250 nm), which also emphasise on the influence of polar substituents of the dimers (Figure S4-S6, ESI). Overall, the aggregation of dimers could be attributed to the self-assembly of molecules, the Vander waals force of attraction and polar group interaction, which help to stack one above the other in the formation of hypsochromic (H)-aggregates (Figure 3).