Temperature photovoltaic dependencies have been measured at 90-350 K for a single-junction GaAs-based p-i-n solar cell and for a similar solar cell with imbedded in i-region In0.4Ga0.6As quantum ...objects. A theoretical approach for analyzing temperature dependencies of open circuit voltage has been proposed. A dethermalization of quantum objects has been observed at temperatures below 170 K, and the temperature of full dethermalization is estimated to be 80 K. It has been shown that dethermalized quantum objects are not involved in the photovoltaic process and may cause photocurrent losses, while, when thermalized, quantum objects give a photocurrent increment. It has been found that the energy difference between optic transitions in GaAs and in quantum objects is independent on temperature. Analysis of the temperature dependencies has allowed for the estimation of effective band gap energy of quantum objects which, at room temperature, was found to be 1.2 eV.
Studies of electronic transitions in the photoconverters with In0.4Ga0.6As quantum well-dots (QWD) layers have been carried out. It is shown that the quantum yield and electroluminescence spectral ...peaks are well described by e1-lh1 and e1-hh1 optical transitions in the quantum well with the same average composition and thickness. The energy of the optical transitions shifts toward longer wavelengths with an increase in the number of QWD layers. The calculated shifts of electron and hole levels due to the redistribution of elastic strain between In0.4Ga0.6As QWDs and GaAs spacer layers demonstrated a very good agreement with the experimental data.
The fundamental reason for the decrease in solar cell (SC) voltage when introducing nanostructures has been found. It consists in the fact that recombination redistributes between nanostructures and ...bulk GaAs. It has been shown that, by changing the position of the nanostructure medium in p-i-n GaAs SCs, it is possible to partially suppress recombination and improve voltage while maintaining the increase in short-circuit current. The decrease of recombination via nanostructures provides an increase in SC efficiency from 19.87% to 21.94%.
A study of GaAs solar cells (SCs) with various quantum-sized objects has been carried out. In0.2Ga0.8As quantum wells, In0.4Ga0.6As quantum well-dots (QWDs), In0.8Ga0.2As and InAs quantum dots have ...been considered. The increment in photocurrent and the reduction of open-circuit voltage have been calculated using dark IV and spectral characteristics. An analytical model for estimating the efficiency of triple-junction SCs with quantum objects has been described. The calculations have shown that the optimized QWDs have a potential for increasing the efficiency of GaInP/GaAs/Ge SC from 29.8% to 30.8% (AM0, 1 sun) and from 41.6% to 43.1% (AM1.5D, 360 suns).
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