Solar cells energy loss processes

Since there is no energy conversion processing required (i.e. no efficiency losses to convert steam generated by combustion into electricity via a turbine or to convert sunlight to electricity via a photovoltaic cell and then use the electricity to split water by electrolysis), the sunlight is directly used to drive high temperature "brute force" chemical reactions -such as dissociation reactions - at high efficiency. Overall solar-thermal efficiencies approach 50%. 

Silicon solar cells suffer from about 50% losses because the solar spectrum does not match well with silicon absorption. Photons with wavelengths longer than the band gap (for multicrystalline silicon, mSi, Eg - 1.1 eV) are wasted, whereas shorter wavelengths are absorbed but the excess energy is lost due to thermahzation of the electrons. The optimum wavelength for absorption is 1,100 nm. Effort has therefore been directed to tailor incident radiation upon the cell by using a front panel so that the optimum response is achieved. It therefore entails that both upconversion and downconversion processes are required to be apphed to modify the energies of incident photons. 

One of the strategies is to minimize the diffusion path of exitons (botmd states between an electron and electron hole) generated by photons hitting the active material in a photovoltaic cell. Once separated, holes and electrons should reach anode and cathode electrodes, respectively. During the process, recombination of holes and electrons lead to energy losses via thermal dissipation. In order to reduce such losses, minimizing the diffusion paths of exitons by means of BCP-derived nanostructures may be beneficial. To this end, a thin solid-state dye-sensitized solar cell (ssDSSC) with a 3D gyroidal titania network was fabricated (see Fig. 12) [37]. In contrast to typical disordered nanoparticle networks, the ordered mesoporous... 

The quantities Pn and p i are properties of the material and are temperature dependent. For c-Si typical values for ph and p are 500 cm s" in n-type Si and 1200 in cm s in p-type Si, respectively.i i The efficiency of the device is the ratio of power output to input power. The thermodynamic limit to solar energy conversion is 93%. The loss processes in a simple p-n junction solar cell are shown in Figure 3.4. Photons with energy lower than the band gap do not have sufficient energy to promote an electron to the conduction band and therefore do not contribute to the power output. Process 1 occurs when a photon with... 

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