Solar cells back reflector

Figure 13 shows typical results of the degradation of crystalline Si solar cells having a back surface field and reflector structure (Si-BSFR), which were qualified by National Space Development Agency of Japan (NASDA) for space usage, when irradiated by 10-MeV protons and 1 -MeV electrons. The pn junction of the cell samples, with a size of 2 cm x 2 cm X 50 pm, was fabricated by phosphorus (P) doping to a depth of 0.15 pm into boron... 

ZnO can be advantageously used as TCO layer in various kinds of thin film silicon solar cells, either as back or as front contact, or even as an intermediate reflector between the amorphous and the microcrystalline p-i-n junctions, within the micromorph tandem solar cell [58] (see also Chap. 8). Figure 6.48 illustrates the various possibilities for using a ZnO layer within a thin film silicon solar cell. In the present paragraph, we will comment about the use of CVD ZnO both as front contact (or window layer) and also as back contact (or part of the back reflector). 

Fig. 8.25. Quantum efficiency QE and cell absorption (1 — R) curves of pc-Si H pin solar cells (i-layer thickness 1.2 pm, ZnO/Ag back reflector) for front ZnO Al with different thickness 330nm (dashed), 870nm (dotted), and 1 370nm (solid). R is total cell reflectance. Sheet resistance of the front contacts as well as FF and Jsc of the solar cells are given in Table 8.4...

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. 

Tabuchi et al. [241] applied boron-doped ZnO films combined with a ZnO/AgAl back reflector to amorphous silicon solar cells. They observed the following optimal characteristic values = 18.6 mAcm , = 0.893 V, efficiency 11.9%, fill factor = 0.715. 

Ghannam M, Abouelsaood A, Kuzma I, Duerinekx F, Poortmans J (2006) Optical modeling of capped multilayer porous silicon used as a back. In Reflector in thin-fihn silicon solar cells proceedings of the IEEE 4th world conference on photovoltaic energy conversion, Hawaii,... 

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