Tandem solar cells

A smaller class of type II alloys of II-VI binaries also exists, including the (CdS) ,(ZnSe)i (CdS) ,(ZnTe)i (CdSe) ,(ZnSe)i (CdS) ,(CdTe)i-. (CdSe)x(CdTe)i i , and (CdS) c(ZnS)i i systems, which transform at some critical composition from the W to the ZB structure. Importantly, the transition temperatures are usually well below those required to attain a thermodynamically stable wurtzite form for the binary constituents (e.g., 700-800 °C for pure CdS and > 1,020 "C for pure ZnS). The type 11 pseudobinary CdxZni jcSe is of considerable interest in thin film form for the development of tandem solar cells as well as for the fabrication of superlattices and phosphor materials for monitors. The CdSe Tei-x alloy is one of the most investigated semiconductors in photoelectrochemical applications. 

FIG. 72. Schematic cross-section of (a) a single junction p-i-n o-Si H superstrata solar cell and (b) a tandem solar cell structure. (From R. E. I, Schropp and M. Zeman. "Amorphous and Microcrystalline Silicon Solar Cells—Modeling, Materials and Device Technology," Kluwer Academic Publishers, Boston, 1998, with permission.)... 

The amorphous silicon tandem solar cells consisted of three n-i-p a-Si H cells grown by plasma-enhanced chemical vapor deposition (PECVD) [126]. The a-Si H cell area was 0.5 cm2. 

Jiang, C.-W. Green, M. A. 2006. Silicon quantum dot superlattices Modeling of energy bands, densities of states, and mobilities for silicon tandem solar cell applications. J. Appl. Phys. 99 114902-114909. 

A. De Vos, Detailed balance limit of the efficiency of tandem solar cells,... 

Figure 28 Tandem solar cell where monodirectional antenna systems with three dyes are put between two w-type semiconductors with different hand gaps.

Olson JM (1987) Current and lattice matched tandem solar cell. US Patent 4667059... 

Bertness KA, Kurtz SR, Friedman DJ, Kibbler AE, Crammer C (1994) 29.5% efficient GalnP/GaAs tandem solar cells. Appl Phys Lett 65 989-99... 

Cheyns D, Rand BP, Heremans P (2010) Organic tandem solar cells with complementary absorbing layers and a high open-circuit voltage. Appl Phys Lett 97 3... 

Schueppel R, Timmreck R, Allinger N, Mueller T, Fumo M, Uhrich C, Leo K, Riede M (2010) Controlled current matching in small molecule organic tandem solar cells using doped spacer layers. J Appl Phys 107 6... 

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). 

Microcrystalline Silicon and Micromorph Tandem Solar Cells... 

Here we describe the layer structure for single junction as well as for tandem solar cells consisting of a-Si H and pc-Si l I. Further, this section will deal with the stability of silicon thin film solar cells and the possibility to reduce degradation by special design. 

Fig. 8.4. Layer structure of single junction n-i-p (substrate) and p-i-n (superstrate) solar cells. Also included is an amorphous/microcrystalline tandem solar cell structure...

As already mentioned in Sects. 6.3.1.2 and 8.2.3, ZnO can be used as an intermediate reflector in a-Si H/ j,c-Si H tandem solar cells between top and bottom cell to increase the current in the thin amorphous silicon top cell [14,15]. As a result, the thickness of the a-Si H top cell can be reduced to improve the stability of the cell upon light induced degradation. Recent progress has even lead to improved light utilization and higher short circuit current density by an optimized intermediate reflector [16]. However, this intermediate reflector might consist of another material than ZnO. 

Figure 19.12 Left. Structure of the tandem solar cell based on pentacene and Ceo with a thin, discontinuous evaporated silver layer Incorporated for efficiency improvement. Right Power efficiency versus excitation wavelength for tandem solar cells with 2 nm silver middle layer (solid circles) and without the silver layer (open circles). The right hand scale is for the ratio of efficiency of the two cells to illustrate the significant difference in dependence on excitation wavelength. Reprinted from reference 63 with permission of the SPIE.

Figure 7.10 Tandem solar cell structure for polymer blend solar cells, based on the design demonstrated by Hadipour et al. (2006). In this all-solution-processed device, the top cell consists of a polymer PCBM bulk heterojunction with an absorption maximum of 550 nm and preferentially absorbs short-wavelength light, while the bottom cell is made from a bulk heterojunction of PCBM with a red-absortring polymer and absorbs longer-wavelength light. The composite gold-PEDOT PSS internal layer connects the two cells in...

A polymer tandem solar cell with 10.6% power conversion efhciency. Nat. Commun. 4,1446. 

Figure 17 shows the schematic cross-sectional view of a GaAs/Si tandem solar cell. It consists of w -GaAs buffer layer. 

Tab. 3 Photovoltaic properties of GaAs/Si tandem solar cell with 1000°CTCA...

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