Abstract
A three-dimensional computer simulation of flexible double-junction solar cells (SC) consisting of Si wires and p-i-n a-Si:H structures was carried out. The performance dependence on geometrical and electrical parameters was calculated. With an increase in the height of the Si wires, the open-circuit voltage ( V OC ) decreases monotonically for both the bottom Si and the top p-i-n a-Si:H junctions. The short-circuit current density ( J SC ) for the top p-i-n a-Si:H junction increases sharply with Si wire height, and then, it goes into saturation at a wire height of more than 10-15 μm. The absolute value of J SC increases (from 10.2 to 12.7 mA/cm2) with a decrease in the wire diameter (from 2 to 0.5 μm). For the bottom junction based on Si wires, the dependence of J SC on the wire height is determined by the charge carrier lifetime, doping level, and diameter, which can be associated with the effect of complete inversion of the Si wire conductivity type. For tandem SCs, the optimal wire height is 10 μm, at which efficiency of 14% can be achieved for structures based on Si wires with a diameter of 0.5 μm and a charge carrier lifetime of 10 μs. The practical implication of the developed design was experimentally demonstrated.
Highlights
The upcoming energy engineering is projected to rely heavily on renewable energy sources such as wind and solar power
The use of silicon only or compounds of the III-V type as a base does not ensure converting the entire spectrum of solar radiation, because the photons with energies less than the bandgap (Eg) of the active region material do not participate in the generation of the electron-hole pairs
The calculation of the bottom junction performance has shown that in the case of high values of minority charge carrier (MCC) lifetime (1 ms) an increase in the height of the silicon wire is accompanied by a significant increase in the shortcircuit current density (JSC) and a slight decrease in the open-circuit voltage (VOC) (Figure 4)
Summary
The upcoming energy engineering is projected to rely heavily on renewable energy sources such as wind and solar power. The use of silicon only or compounds of the III-V type as a base does not ensure converting the entire spectrum of solar radiation, because the photons with energies less than the bandgap (Eg) of the active region material do not participate in the generation of the electron-hole pairs. The photons with energies higher than Eg heat the semiconductor due to light-generated charge carrier thermalization. The solution to this problem was the approach in which the solar cell includes several active regions—semiconductors with different values of Eg, arranged in decreasing order. A flexible solar cell could cover the International Journal of Photoenergy
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