Investigation of quantum dot enhanced triple junction solar cells

InAs quantum dots have been incorporated into the middle junction of an InGaP/(In)GaAs/Ge triple junction solar cell (TJSC) on four inch wafers, in aims of band gap engineering a high efficiency solar cell to even higher limits. Results of QD growth on 4” diameter Ge templates gave densities near 1×1011 cm−3 and QD height between 2–5 nm. Arrays of 10 layers of InAs QDs have been grown between the base and emitter in the middle cell of a full triple junction solar cell. Control triple junction cells that received growth interrupts without QD growth showed similar results (within 5 mV open circuit voltage) to standard triple junction cells without an interrupt. Integrated current of the (In)GaAs junction with 10 layers of strain balanced InAs QD layers shows a gain of 0.37 mA/cm2 beyond the band edge. One sun AM0 current-voltage measurements of QD TJSC show an efficiency of 26.9% with a Voc of 2.57 V.