Pushing Radiation Hardness and Qualification of Ultrathin Silicon Solar Cells

Solestial (former Regher Solar) proposes this SBIR project to mature ultrathin silicon (UT-Si) solar cell technology to achieve TRL 7 and transition to higher TRL followed by injection into both NASA and commercial missions.Currently, UT-Si cells manufactured by Solestial have a 20% Beginning-of-Life (BOL) efficiency positioning them between Copper-Indium-Gallium-Selenide (CIGS) and Epitaxial Lift Off Inverted Metamorphic (ELO-IMM) thin film solar cells, which are considered for flexible solar blankets. With several practically attainable improvements we expect UT-Si solar cells to reach 22% BOL efficiency within a year. Their End-of-Life (EOL) efficiency drops insignificantly by 3% over a 10 year when exposed to space radiation making them very attractive for space applications. By effectively mitigating radiation damage UT-Si cells can achieve EOL efficiency of ELO-IMM cells while cost-competitive with CIGS cells making them the optimum choice for flexible solar arraysamong all thin filmtechnologies. This project leverages an improved understanding of radiation-induced defects in c-Si developed in the last 3 years within the efforts to fabricate more radiation-hard Si detectors for the Large Hadron Collider. The main proposed innovations include: (1) leveraging defect engineering to passivate radiation-induced defects, (2) conducting the electron/proton irradiation experiments that closely simulate space conditions with solar cell illumination under the load, and (3) performing qualification experiments, including stress testing (temperature cycling in particular) to be qualified for space use, (4) Phase II-E will work with development partners to integrate UT-Si cells into ongoing missions and achieve TRL 8. Phase II of this project demonstrated the feasibility ofthe proposed innovations. We will collaborate with blanket manufacturers to package UT-Si solar cells in CICs and blankets and conduct comprehensive qualification tests to achieve TRL 7.
Benefits: UT-Si solar cells can be integrated into novel flexible solar array deployment systems to meet NASA solar array specific power (250 W/kg) and stowed volume efficiency (50 kW/m3) goals. At the same time UT-Si solar cells have a potential to also meet NASA goals for the long-term operation in high radiation environment (1 MeV 6e15 e/cm2). Together this will make UT-Si solar cell technology an ideal choice for several NASA projects including LISA solar array, Vertical Lunar Solar Arrays and large scale solar arrays for Solar Electric Propulsion. The main advantage of UT-Si technology is compatibility with high volume manufacturing and a low manufacturing cost. Production of UT-Si solar cells can be quickly scaled to 100 MW/year to meet the demand of the growing space industry. The example applications include satellite mega constellations and space based solar power that will need tens of MW of affordable space-stable solar cells.