High Efficiency Quantum Dot III-V Multijunction Solar Cell for Space Power

We are proposing to utilize quantum dots to develop a super high-efficiency multijunction III-V solar cell for space. In metamorphic triple junction space solar cells, pioneered by Essential Research, Inc., the InGaAs junction or bottom cell of the three-cell stack is the current limiting entity. In Phase I of this program, we demonstrated that InAs quantum dots can be formed by MOVPE, and then incorporated in an InGaAs cell to provide sub-gap absorption and thus improve its short-circuit current. For the Phase II work, we propose to optimize this quantum dot InGaAs cell, and develop a three-cell stack to achieve a space solar cell whose efficiency would dramatically exceed current SOA standards. A theoretical estimate predicts that a InGaAlP(1.95 eV)/InGaAsP(1.35 eV)/InGaAs(1.2 eV) triple junction cell incorporating quantum dots to improve the bottom cell current would have an efficiency exceeding 40%.Quantum dots will allow NASA not only to improve device efficiency by expanding the spectral response of individual cells, but to improve the temperature coefficients and radiation tolerance as well. This is extremely important as NASA attempts to increase array specific power with new concentrator designs and continues to expand the range of environments to be encountered in future missions.