Dethermalization of carriers in GaAs solar cells with quantum objects

Abstract

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.