Silicon p-n junction solar cell

Figure 11.4 The working mechanism of a silicon p-n-junction solar cell...

S.C. Jain, E.L. Heasell, D.J. Roulston, Recent advances in the physics of silicon P-N junction solar cells, in T.S. Moss, et al. (Eds.), Progress in Quantum Electronics, Pergamon Press, Oxford, 1987, pp. 105-204. 

Fig. 11.6 The working mechanism of a silicon p-n junction solar cell. Adapted with permission from (Wardle B, 2009 Principles and Applications of Photochemistry, Wiley, p. 217). Copyright (2009) John Wiley Sons...

The DSSC differs substantially from silicon p-n junction solar cells by the fact that no holes are formed in the VB of the semiconductor. 

M.A. Shibib, F.A. Lindholm and J.G, Possum. Auger recombination in heavily doped shallow-emitter silicon p-n-junction solar cells, diodes and transistors I.E.E.E. Trans. ED 26, 1104 (1979). 

If the thickness of the insulator is reduced below about 10 A the concept of a tunnel MIS diode apparently becomes invalid, based at least on experimental evidence, and these thin structures perform as basic Schottky barriers. Above 28-30 A the diodes behave as equilibrium tunnel diodes. From Fig 7a it can be observed that even in the minority carrier regime under forward bias the region over which ideal p-n junction diode behaviour is predicted is insulator thickness dependent. Since in the case of p-n junctions in silicon under normal AMI illumination about 0.5 - 0.7 V is developed across the junction this means that for significant conversion efficiencies in these mi MIS devices insulator thickness should not exceed about 20 A. At greater thickness there will be some suppression of the photo-current due to the shape of the I-V characteristic rather similar to that observed in p-n junction solar cells with large series resistance. 

Assuming that an efficient D-A type of molecule can be synthesized, it should be possible to deposit these molecules as a monolayer onto a glass slide coated with a metal such as aluminum or a wide bandgap semiconductor such as Sn(>2. With the acceptor end of the molecule near the conductor and with contact to the other side via an electrolyte solution it should be possible to stimulate electron transfer from D to A and then into the conductor, through an external circuit and finally back to D through the electrolyte. This would form the basis of a new type of solar cell in which the layer of D-A molecules would perform the same function as the p-n junction in a silicon solar cell (50). Only the future will tell whether or not this concept will be feasible but if nature can do it, why can t we ... 

This layer is placed on top of a thicker layer of boron-doped silicon (P-layer with positive character). These layers are connected by the P-N junction. When sunlight strikes the surface of the PV cell, an electric field is generated, which provides momentum and direction to the light-stimulated electrons, resulting in a flow of current when the solar cell is connected to an electric load. 

Although ZnO has also been applied in so-called amorphous/crystalline heterojunction solar cells consisting of a (doped) silicon wafer and thin doped a-Si H layers to build the p-n junction, we will restrict ourselves here to solar cells and modules with amorphous and/or microcrystalline absorber layers, i.e., real thin film silicon solar cells. For detailed information on the use of ZnO in crystalline silicon wafer based devices, the reader is referred to the literature (see e.g. [23,24]). 

Abstract Photovoltaic cells have been dominated so far by solid state p-n junction devices made from silicon or gallium arsenide wavers or thin film embodiments based on amorphous silicon, CdTe and copper indium gallium diselenide (CIGS) profiting from the experience and material availability of the semiconductor industry. Recently there has been a surge of interest for devices that are based on nanoscale inorganic or organic semiconductors commonly referred to as bulk junctions due to their interconnected three-dimensional structure. The present chapter describes the state of the art of the academic and industrial development of nanostructured solar cells, with emphasis in the development of the dye-sensitized nanocristalline solar cell. 

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