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The TCO layer for SHJ cells should ideally have a high work function [85] (ie. the energy difference between the Fermi level and the Vacuum level) to prevent formation of a parasitic Schottky barrier at the interface between the TCO and the p-type amorphous layer.
Thermophotovoltaic (TPV) energy conversion is a direct conversion process from heat to electricity via photons. A basic thermophotovoltaic system consists of a hot object emitting thermal radiation and a photovoltaic cell similar to a solar cell but tuned to the spectrum being emitted from the hot object. [1]
In a basic Schottky-junction (Schottky-barrier) solar cell, an interface between a metal and a semiconductor provides the band bending necessary for charge separation. [1] Traditional solar cells are composed of p-type and n-type semiconductor layers sandwiched together, forming the source of built-in voltage (a p-n junction ). [ 2 ]
However, the solar frequency spectrum approximates a black body spectrum at about 5,800 K, [1] and as such, much of the solar radiation reaching the Earth is composed of photons with energies greater than the band gap of silicon (1.12eV), which is near to the ideal value for a terrestrial solar cell (1.4eV). These higher energy photons will be ...
For a two layer cell, one layer should be tuned to 1.64 eV and the other at 0.94 eV, with a theoretical performance of 44%. A three-layer cell should be tuned to 1.83, 1.16 and 0.71 eV, with an efficiency of 48%. A theoretical "infinity-layer" cell would have a theoretical efficiency of 68.2% for diffuse light. [11]
Later cells have utilized In 0.015 Ga 0.985 As, due to the better lattice match to Ge, resulting in a lower defect density. [citation needed] Due to the huge band gap difference between GaAs (1.42 eV), and Ge (0.66 eV), the current match is very poor, with the Ge junction operated significantly current limited. [citation needed]
Most photovoltaic cells (e.g. silicon based) suffer from a drop in efficiency with increased cell temperatures. Each Kelvin of increased cell temperature reduces the efficiency by 0.2–0.5%. [5] Therefore, heat removal from the PV cells can lower their temperature and thus increase the cells' efficiency.
The energy bandgap between these orbitals determines which wavelength(s) of light can be absorbed. Unlike in an inorganic crystalline PV cell material, with its band structure and delocalized electrons, excitons in organic photovoltaics are strongly bound with an energy between 0.1 and 1.4 eV. This strong binding occurs because electronic wave ...