Regher Solar proposes this SBIR project to mature ultrathin silicon (UT-Si) solar cell technology to achieve TRL 6 and quickly transition to TRL 7,8 followed by injection into both NASA and commercial missions. At present UT-Si cells manufactured by Regher Solar have a 20% Beginning-of-Life (BOL) efficiency which is exactly in between Copper-Indium-Gallium-Selenide (CIGS) and Epitaxial Lift Off Inverted Metamorphic (ELO-IMM) thin film solar cells that are currently considered for making flexible solar blankets. With several practically attainable improvements UT-Si solar cells will reach 22% BOL efficiency in 2 years. However, the End-of-Life (EOL) efficiency of UT-Si cells drops substantially when exposed to space radiation making them less attractive for the use in space. If radiation damage is mitigated, UT-Si cells can achieve EOL efficiency of ELO-IMM cells while being as inexpensive as CIGS cells making them the optimum choice for flexible solar arrays among all thin film technologies.
This project will leverage an improved understanding of radiation-induced defects in c-Si that was developed in the last 3 years within the effort to fabricate more radiation hard Si detectors for the Large Hadron Collider. The main proposed innovations include: (1) using defect engineering to passivate radiation induced defects, (2) further reducing solar cell thickness from 20 to 10 microns to improve the effectiveness of passivation, and (3) utilizing active defect elimination methods that can be periodically applied to the solar cells in space.
Phase I of this project will demonstrate the feasibility of the proposed innovations and will conduct comprehensive electron and proton irradiation testing. Phase II will collaborate with blanket manufacturers to package UT-Si solar cells in CICs and blankets and conduct complete qualification to achieve TRL 6. Phase II will also work with development partners to integrate UT-Si cells into ongoing missions and achieve TRL 7,8.
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.