Electrical and optical modeling

Next to optical interference there is also eleetrical interference. In a series-connected tandem solar cell the conservation of charge dictates that the photocurrent through the device must be eonstant and that the voltages of the subcells add up to give the voltage of the tandem device this is represented for current density and voltage by the relations  

The starting point is to determine the J-V eharaeteristics of the two single junction cells as a function of layer thiekness and the optical constants [n, k) of the photoactive layers. Using optieal modeling of the layer staek of the single junetions, it is then possible to ealeulate the IQE as the ratio 

These approaches optimize the tandem cell by varying the thickness of the active layers. It is also possible to balance the subcells by varying the thickness of charge transport layers. These can act as optical spacers to adjust the electrical optical field in the layer stack such that it maximizes in the photoactive layers. This approach is particularly useful for vacuum processed small molecule tandem cells where the low charge mobility dictates the use of thin photoactive layers of 20-50 nm.  

---

Fig. 9.8. (a) FBZ for four regular layers of nickel atoms (a crystal surface model) (b) the band structure for this system. We see that we cannot understand much just a horrible irregular mess of lines. All the band structures look equally clumsy. Despite this, from such a plot we may determine the electrical and optical properties of the nickel slab. We will see later on why the bands have such a mysterious form. R. Hoffmann, Solids and Surfaces. A Chemist s View of Bonding in Extended Smtcntres , VCH Publishers, New York, 1988 VCH Publishers. Reprinted with permission of John Wiley Sons, Inc. 

In this chapter, we present the physical properties of cathodes materials and verify the applicability of the rigid-band model for intercalation compounds with a layered structure namely transition-metal chalcogenides MX2 (M = Ti, Ta, Mo, W X = S, Se) and oxides LLWO2 (M = Co, Ni) as well. Electrical and optical properties are investigated. For some materials, we observe different degrees of irreversibility in the intercalation process and lattice evolution to the complete destruction of the host. Since the purpose here is the study of the materials in the framework of... 

---