Effect of Dot-Height Truncation on the Device Performance of Multilayer InAs/GaAs Quantum Dot Solar Cells

The effect of dot-height truncation on the device performance of multilayer InAs/GaAs quantum dot solar cells is investigated. The different structures were grown by chemical beam epitaxy, and an indium-flush process is used to control the dot height. A series of ten-layer samples with dots truncated at a height of 5 and 2.5 nm, respectively, are studied. Luminescence, atomic force microscopy, and high-resolution scanning transmission electron microscopy results indicate that the quantum dot properties are preserved up to the tenth layer for both structures. Under 1-sun illumination, the truncation of the dot height to 2.5 nm increased the short-circuit current density by 0.7 mA/cm(2) and the open-circuit voltage by 31 mV. From the external quantum efficiency curves, limited to wavelengths > 500 nm, a 1.46-mA/cm(2) current density enhancement is found over a GaAs reference cell. At least 45% of this enhancement has been attributed uniquely to the presence of quantum dots in the structure.