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Photosynthesis
Published in Thomas M. Nordlund, Peter M. Hoffmann, Quantitative Understanding of Biosystems, 2019
Thomas M. Nordlund, Peter M. Hoffmann
We have reached the end of our consideration of the primary energetic processes of purple bacterial photosynthesis. We have left the electron poised, after the first charge separation, at a bacteriopheophytin site for further transfer. The quantum efficiency of conversion of photons to electrons is above 95%. The (free) energy conversion efficiency from first excitation to first separated charge is roughly 70%–75% for absorption of a 700–800 nm photon. The next task for the reaction center is to move separated charge to a site where its energy can generate needed chemical energy or oxygen. Purple bacteria do not generate O2, but the PS-II PSU we have introduced does. The PS-II complex is found in cyanobacteria and green plants and includes, in addition to an O2-generating site, many of the general features of the features of the purple bacteria: light-harvesting chlorophylls (though not in ringlike assemblies), a reaction center, special pair of chlorophylls, and accessory pigments. These pigments are displayed in Figure 10.24 for the cyanobacterium Thermosynechococcus elongatus. We leave for homework the exploration of this structure in terms of its special pair and manganese oxygen center.27
Sources, Detectors, and Recording Media
Published in Rajpal S. Sirohi, Introduction to OPTICAL METROLOGY, 2017
Spectral sensitivity depends on the material composition of the detector. Essentially, the absorption coefficient of the material varies with wavelength being smaller at the longer wavelengths. Ideally, an incident photon should generate one electron but due to losses arising from reflection and material imperfections, and so on, 1 photon/s does not create 1 electron/s. Responsivity takes into account all the factors and hence is a measure of how 1 W of optical power is converted to an electrical current and is expressed in units of amperes per watt. Responsivity increases with wavelength unlike the absorption coefficient. Since the number of electrons created is proportional to the number of photons, the same watt of optical power has more photons at larger wavelengths than at the shorter wavelengths. Quantum efficiency is the ratio of the number of electrons generated by the detector to the number of photons incident on the detector. Dark current is the small current that flows through the photodetector even when there is no radiation incident on it. The magnitude of dark current depends on temperature and contributes to the noise in the electrical output of the detector. Rise time of a detector is a measure of its response to an impulse and is measured by the time it takes to reach 63.2% of its steady-state value.
Introduction to Optoelectronic Device Principles
Published in Sam-Shajing Sun, Larry R. Dalton, Introduction to Organic Electronic and Optoelectronic Materials and Devices, 2016
The responsivity depends on the light wavelength and the spectral responsivity curve Rph(λ) is one of the key performance characteristics of photodiodes (Figure 2.4). It is related to the quantum efficiency ηph of the photodetector, which gives the number of electrons collected (Iph/e) relative to the number of incident photons (Pin/hν). The maximum possible quantum efficiency is 100% when each incident photon generates one electron that arrives in the doped regions. Practically, the quantum efficiency is limited by the surface reflectance R and by the absorption layer thickness d () ηph=(1−R)[1−exp(−αd)]
Effects of beam splitting on photovoltaic properties of monocrystalline silicon, multicrystalline silicon, GaAs, and perovskite solar cells for hybrid utilization
Published in International Journal of Green Energy, 2023
Yu Gao, Xiaoxiao Yang, Zhongchao Tan, Xingyuan Yang, Yanguo Zhang, Hui Zhou, Qinghai Li
Solar cells were tested with and without the beam splitters using a solar simulator (SS-F5-3A, Enli Technology Co. Ltd., Taiwan, China) with 3A standard to determine their short-circuit current density (JSC), open-circuit voltage (VOC), fill factor (FF), maximum power (Pmax), and power conversion efficiency (PCE). The solar simulator operates with 1 sun AM1.5 G illumination (100 mW/cm2). External quantum efficiency (EQE) was measured using a quantum efficiency analyzer (QE-R2, Enli Technology Co. Ltd., Taiwan, China). The EQE of some wavelength is defined as the ratio of numbers of electrons collected at short circuit and incident photons at that wavelength (Gilot, Wienk, and Janssen 2010). EQE is a useful indicator of applicability to the solar cells for beam-splitting hybrid system. All tests were repeated three times or more to ensure reproducibility.