DESIGN, FABRICATION AND ANALYSIS OF SIGE SOLAR CELL IN A GALLIUM ARSENIDE PHOSPHIDE - SILICON GERMANIUM DUAL JUNCTION SOLAR CELL ON SI SUBSTRATE

摘要

A Si_(.15)Ge_(.85) solar cell under GaAsP top cell can lead to as much as 8.8% absolute efficiency gain for a GaAsP-SiGe tandem structure under 20 Suns. In this work, low bandgap Si_(1-x)Ge_(x) solar cells are designed, fabricated, characterized and analyzed. Numerical and analytical methods are introduced to demonstrate the SiGe solar cells' performance limits and examine the trade-offs between Ⅳ performance, cell's structures and material composition. An efficiency of 1.7% with a Voc of 265 mV, a Jsc of 9.9 mA/cm~2 and a FF of 64% is achieved with the Si_(.18)Ge_(.82) cell under a GaAsP top cell. The highest Jsc measured without SiO_2 back surface reflector, back texturing or anti-reflection coating is 12.9 mA/cm~2 from a Si_(.12)Ge_(.88) cell. By introducing 5% front broadband reflection, the expected Jsc will be 19.4 mA/cm~2 for the same cell. By adding back surface field, a 415 mV Voc under 20 Suns is achieved. Implementing light trapping can lead to the target Jsc of 21 mA/cm~2.