Research Information System
Thesis Type: Postgraduate
Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey
Approval Date: 2011
Student: GÖKHAN ŞENAY
Supervisor: TUĞBA SELCEN NAVRUZ
Open Archive Collection: AVESIS Open Access Collection
Abstract:The two most important power-loss mechanism in single bandgap cells are the inability to absorb photons with energy less than the bandgap and thermalization of photon energies exceeding the bandgap. These two mechanism alone amount to the loss of about half of the incident solar energy in photovoltaic conversion. Last generation solar cells aim to increase efficiency by harnessing some of these wasted energy. In this thesis, theoretical analysis were carried out on the multi-junction solar cells, the only ones ever been realized among the last generation solar cells. Detailed Balance Model was used in all analysis performed under black body radiation. To be able to realize efficiency improvement in multi-junction solar cells, efficiency analysis on single bandgap solar cell was performed firstly.Maximum efficiency in the single bandgap solar cell was calculated as %31.162 for EG=1.31 eV. In the double junction monolithic solar cell, maximum efficiency was obtained as %42.668 for EG1=1 eV and EG2=1.71 eV. In the triple junction monolithic solar cells in which Ge (EG1=0.7 eV) is considered to have been used as substrate and third layer, maximum efficiency was obtained as %48.27 for EG2=1.21 eV and EG3=1.87 eV. It is also observed that efficiency increases logarithmically with light intensity.Current matching process was performed on the double and triple junction solar cells by adjusting the top-cell thicknesses. In the double junction GaAs (1.42 eV)/Ge (0.7 eV) and triple junction GaInP (1.9 eV)/GaInAs (1.4 eV)/Ge (0.7 eV) solar cells, it was seen that efficiency increases as the top-cell is thinned to a constant value.Finally, the effect of Auger generation and recombination on the efficiency of single junction and double junction monolithic solar cells with optimum bandgaps and GaAs (1.42 eV)/Ge (0.7 eV) solar cells has been investigated. In the single junction solar cell, it was seen that Auger mechanism, depending on the multiplication probability (σ), led to significant increase in the efficiency. In the double junction monolithic solar cells with optimum bandgap and GaAs (1.42 eV)/Ge (0.7 eV) solar cells, it was observed that Auger mechanism have almost no effect on the efficiencies. The top cell in double junction monolithic solar cells having been thinned, it was witnessed that Auger mechanism made significant contribution on the efficiencies. It was concluded from here that the effect of Auger mechanism on the efficiency of multi-junction monolithic solar cells depends on the top cell thickness.