Abstract:
Various ways to harvest photons in the solar spectrum and heat energy from the surroundings have been considered by utilizing solid state physics principles. A graded bandgap multi-layer solar cell has been designed to absorb UV, visible and infrared radiation, and to combine impact-ionization and impurity photovoltaic (PV) effect to enhance photo-generation of charge carriers and the collection. The above theoretical concepts were experimentally tested using the well researched material system, GaAs/AlxGa(1-x)As. The highest reported Voc ∼ 1175 mV together with the highest possible fill factors (FFs) in the mid 80%'s, have been achieved for the initial devices. The overall efficiency achieved using only two growths is ∼ 20%. As expected from the initial design, the impurity PV effect is experimentally observed producing Voc values in the range of 650-900 mV under complete darkness for the GaAs/AlxGa(1-x)As based devices. Both the theoretical concepts and experimental results are presented in this paper.