Interstitial Light Trapping and Optical Confinement in Multijunction Solar Cells
Erin Cleveland1, Nicole Kotulak1, Stephanie Tomasulo1, Phillip Jenkins1, Alexander Mellor2, Pheobe Pearce2, Ned Ekins-Daukes3, Michael Yakes1
1Naval Research Laboratory, Washington, DC, United States
/2Imperial College, London, United Kingdom
/3University of New South Wales, Sydney, Australia

Abstract  —  High efficiency photovoltaic devices for space applications are desirable due to the specific power (W/kg) they provide, which in turn enables a higher power payload. In addition to providing high specific power, devices should be resilient to radiation exposure to maintain performance over the lifetime of a mission. Traditional solar cells are microns thick in order to absorb most of the incident solar illumination. We recently demonstrated an ultra-thin solar cell with increased radiation tolerance as compared to a traditionally thick absorber counterpart. However, as the active region of the device was reduced so was the absorption with respect to state of the art devices. Therefore, we propose an interstitially placed light trapping design between two subcells of a multijunction device, which implements natural nanosphere photolithography to fabricate a micropillared diffraction grating, a transparent spacer layer and a distributed Bragg reflector (DBR). Natural nanosphere photolithography is a process that utilizes self-assembly in order to pattern materials at the nanoscale. We will discuss the fabrication process to produce a texturized surface using nanosphere natural photolithography and illustrate the effectiveness of integrating light trapping structures for enhanced optical confinement within an ultra-thin solar cell design.