Efficiency Evaluations of Dual Junction IV-VI Semiconductor Thermo photovoltaic Cells
Abstract – Thermo photovoltaic (TPV) device can be used to convert energy stored thermally in molten silicon. We model the performance of TPV devices that utilize Pb0.80Sr0.20Se/Pb0.81Sn0.19Se /Pb0.80Sr0.20Se IV-VI semiconductor multiple quantum well materials in a dual junction device configuration. Both junctions benefit from degeneracy splitting of electron and hole energy levels into two sub bands corresponding to the normal and oblique valleys in the  growth direction resulting in reduced dark current density values. Using quantum well calculations and including strain effects the inter band optical transition energy gaps for different well widths were calculated to be 455 meV, and 346 meV, for well widths of 2.10 nm and 3.15 nm for the top and bottom junctions, respectively. We calculated the output electric power density and efficiency for each junction as a function of junction thickness. The overall maximum electric power density and efficiency for the device were 5.77 W/cm2 and 20.3% at a junction thickness of 2.1 µm. After matching the short current density throughout the device these values dropped to 3.7 W/cm2 and 13%. To increase these values and maintain a matched short circuit current density we increased the period of the MQW of each junction at the fixed junction thickness of 2.1 µm. As a result, the overall maximum electric power density and efficiency values increased to 7.1 W/cm2 and 25%. Further improvement to the obtained values can be achieved by use of spectrum filtering and back scattering reflectors.
Keywords - Double Junction, Energy Storage, Lead Salts, Thermo photovoltaic cells