Solar cells inhomogeneity

Preliminary measurements with space-resolved PMC techniques have shown that PMC images can be obtained from nanostructured dye sensitization cells. They showed a chaotic distribution of PMC intensities that indicate that local inhomogeneities in the preparation of the nanostructured layer affect photoinduced electron injection. A comparison of photocurrent maps taken at different electrode potentials with corresponding PMC maps promises new insight into the function of this unconventional solar cell type. 

As nearly all the developed ribbon silicon growth techniques result in multicrystalline material, crystal defects play a major role in the solar cell efficiencies obtained on ribbon silicon wafers. There is a general trend for higher defect concentrations with faster ribbon growth, but even within wafers of one growth technique, there is an inhomogeneous defect distribution. In this section, we will introduce the known relevant defects for the three materials under closer examination (EFG, SR and RGS) and their impact for solar cell processing. Especially, interaction between different types of defects must be taken into account to understand the behaviour of the different ribbon silicon materials within the cell process. 

As material quality is inhomogeneous even after gettering and hydrogenation (Fig. 7.7), solar cell results are affected by both good and bad areas. Cell performance in areas of low diffusion length is limited due to recombination in the bulk, whereas rear surface recombination, 5b, can limit carrier collection in good quality areas. 

Importance of the active layer morphology control was first recognized in 2001 for solar cells based on the MDMO-PPV/[60]PCBM composite. Simple replacement of solvent used for active layer casting from toluene to chlorobenzene unproved power conversion efficiency of the devices from 0.9 to 2.5%. A clear understanding of the morphology aspects related to such a remarkable solvent effect appeared in 2(K)4 in a detailed report by Hoppe et al It was shown that MDMO-PPV/[60]PCBM films cast from toluene are rather inhomogeneous and... 

Figure 7. Photocurrent profiles at the same position across a dye sensitized solar cell with inhomogeneous photocurrent distribution. Measurements were done after different periods of illumination with simulated solar light. The photocurrent profiles smooth out during long-term photodegradation, because photodegiadation is faster where large photocurrents are flowing. (Experiment performed with copper-chlorophylline on TlOj) (a) before and (b) after 21 days, and (c) after another 93 days of illumination with simulated solar light.

An example of the modeled electric field intensity profiles of an opaque cell and the corresponding ST-OPV cell are given in Figure 12.3(a). The ST-OPV presented is composed of a PBDTTT-C-T PC7iBM BHJ film sandwiched between an ITO and an ultrathin Ag film (12 nm) transparent electrode, while for the opaque cell a thick Ag film was used as the mirror electrode. The simulations indicate that in both cases the distributions of the electric field inside the solar cells are highly wavelength dependent and inhomogeneous... 

Many phenomena of interest in science and technology take place at the interface between a liquid and a second phase. Corrosion, the operation of solar cells, and the water splitting reaction are examples of chemical processes that take place at the liquid/solid interface. Electron transfer, ion transfer, and proton transfer reactions at the interface between two immiscible liquids are important for understanding processes such as ion extraction, " phase transfer catalysis, drug delivery, and ion channel dynamics in membrane biophysics. The study of reactions at the water liquid/vapor interface is of crucial importance in atmospheric chemistry. Understanding the behavior of solute molecules adsorbed at these interfaces and their reactivity is also of fundamental theoretical interest. The surface region is an inhomogeneous environment where the asymmetry in the intermolecular forces may produce unique behavior. 

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