Solar cells optical simulation

From a theoretical point-of view, significantly higher current densities are feasible, but require further improved front TCO films and perfect mirrors as back reflectors. This is illustrated by the dotted curve in Fig. 8.28, which shows simulations of quantum efficiency for a 1 pm thick pc-Si H solar cell. These simulations reveal a current potential of 29.2 mA cm-2 by improved optical components like reduced parasitic absorption in the front TCO, ideal Lambertian light scattering, dielectric back reflectors, and antireflection coatings on the front side [147]. However, this still has to be achieved experimentally. 

Finally, as it is not possible to experimentally test all the various kinds of surface textures within actual solar cell configurations, it can be useful to use numerical simulations, in order to evaluate the best combination of surface textures and roughness for both front and back TOO layers. The method usually applied for such simulations is to take the main optical properties of each layer of the solar cell (absorption, thickness, haze factor, ADF, surface roughness,. ..), and then to put them all together in order to compute the quantum efficiency curve of the resulting solar cell. Such a task of optically simulating solar cells is very complex and beyond the scope of the present chapter. However, it is important to note here that a numerical simulation is always only an imperfect tool and can in no way fully replace experimental work and measurements on actual solar cells. 

Fig. 8.28. Quantum efficiency and celi absorption (1 -R) of tc-Si H solar cells on ZnO Al films sputtered from targets with different doping levels (0.8 at. % (solid) and 1.6 at. % (dashed)). Optical data of these ZnO Al films are given in Fig. 8.7. Simulation results using improved optical components are also included (dotted) [147]...

A further improvement of MDMO-PPV based bulk heterojunctions was achieved by the application of a new C70 fullerene derivative, which was substituted with the same side chains as PCBM and is therefore called [70]PCBM [170]. Due to the reduced symmetry of C70 as compared to the football sphere (icosahedral symmetry) of Ceo. more optical transitions are allowed and thus the visible hght absorption is considerably increased for [70]PCBM. This led to an improved external quantum efficiency (EQE) of MDMO-PPV based solar cells reaching up to 66% (Fig. 30). As a result the power conversion efficiency was boosted to 3% under AM 1.5 solar simulation at 1000 W/m [170]. 

Andersson and coworkers have prepared solar cells based on blends of poly(2,7-(9-(2 -ethylhexyl)-9-hexyl-fluorene)-fl/t-5,5-(4, 7 -di-2-thienyl-2, l, 3 -benzothiadiazole) (223) and PCBM [416]. The polymer shows a Amax (545 nm) with a broad optical absorption in the visible spectrum and an efficiency of 2.2% has been measured under simulated solar light. The same group has also reported the synthesis of low bandgap polymers 200 (1 = 1.25 eV) and 224 (1 = 1.46 eV) which have been blended with a soluble pyrazolino[70]fiillerene and PCBM, respectively, to form bulk heterojunction solar cells of PCE of 0.7% [417] and 0.9% [418]. Incorporation of an electron-delident silole moiety in a polyfluorene chain affords an alternating conjugated copolymer (225) with an optical bandgap of 2.08 eV. A solar cell based on a mixture 1 4 of 225 and PCBM exhibits 2.01% of PCE [419]. 

Several processable low bandgap PTs containing isothianaphthene units, such as 226, 227, and 228, have been reported for their use in bulk heterojunction PV devices with PCBM, with efficiencies 0.008%, 0.24%, and 0.31%, respectively, under simulated solar illumination [420—422]. A solar cell made from a mixture of 229/PCBM (1 1) led to an efficiency of 0.09% [423]. Polymer 230 presents a larger optical bandgap (2 eV) than that of 229 (1.3 eV) and a 1 1 mixture of 230 with PCBM leads to a PV cell of 0.024% of PCE under the same illumination conditions than for 229. 

All current-voltage characteristics of the photovoltaic devices were measured with a source measure imit in the dark and under simulated solar simulator source was calibrated using a standard crystalline silicon diode. The ciurent-voltage characteristics of Photovoltaic devices are generally characterized by the short-circuit current (/ ), the open-circuit voltage (F ), and the fill factor (FF). The photovoltaic power conversion efficiency (rj) of a solar cell is defined as the ratio between the maximum electrical power and the incident optical power and is determined byEq.(l)[4]. 

The 2D nanostructures, or surface slabs, are suitable for the simulation of the apolar ZnO surfaces and might constitute the basis for the investigation of adsorption of dye-sensitizers onto ZnO [203] which are of interest for dye-sensitized solar cells. Here we performed a systematic investigation of the electronic and optical properties... 

Abstract We review the methods used to simulate the optoelectronic response of organic solar cells and focus on the application of one-dimensional drift-diffusion simulations. We discuss how the important physical processes are treated and review some of the experiments necessary to determine the input parameters for device simulations. To illustrate the usefulness of drift-diffusion simulations, we discuss several case studies, addressing the influence of charged defects on transport in bipolar and unipolar devices, the influence of defects on recombination, device performance and ideality factors. To illustrate frequency domain simulations, we show how to determine the validity range of Mott-Schottky plots for thin devices. Finally, we discuss an example where optical simulations are used to calculate the parasitic absorption in contact layers. 

Pieters BE, Decock K, Burgebnan M, Stangl R, Kirchartz T (2011) One-dimensional electro-optical simulations of thin-fibn solar cells, hi Abou-Ras D, Kirchartz T, Ran U (eds) Advanced characterization techniques for thin fibn solar cells. Wiley-VCH Verlag GmbH... 

Usami A (2000) TheOTetical simulations of optical confinement in dye-sensitized nanocrystalline solar cells. Sol Energ Mat Sol Cells 64 73-83... 

Shown in Figure 21-17 is a regenerative solar cell based on colloidal Ti02, deposited on an optically transparent FTO support. With a suitable sensitizer and redox couple, these materials convert light into electricity with remarkable efficiency (O Regan, 1991). A maximum efficiency of 10.96% has been obtained under air-mass lA (AM 1.5) simulated sunlight with c -Ru(dcb)2(NCS)2, where deb is 4,4 -(COOH)2-2,2 -bipyridine, as a sensitizer and iodide as the electron donor (Nazeeruddin, 1993). 

The MCM has been used to simulate tubular solar photocatalytic reactors, like parabolic troughs (Arancibia-Bulnes et al., 2002a), CPC (Arancibia-Bulnes et al., 2002b), and also of flat plate geometry (Cuevas et al., 2004). Also it has been used to simulate flat lamp reactors (Brucato et al., 2006) or to obtain optical coefficients by comparison with transmission results from an experimental cell (Yokota et al., 1999). 

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