Thin-Film Multijunction Inverted Metamorphic Solar Cells with Light Management for Space Applications

Inverted metamorphic (IMM) solar cells are an attractive power generation source for space-related applications due to their high power conversion efficiency (PCE), however, the beginning-of-life (BOL) PCE declines after radiation exposure to highly energized particles in the space environment as crystalline defects impact carrier transport. Thinning the bottom subcell, which suffers most from crystalline defects, reduces the distance carriers must travel to support power, making the thin-film design tolerant to radiation damage compared to their optically thick counterparts. Light management is essential in these devices as transmission loss occurs after one optical pass through the thinned solar cell. This work focuses on light trapping structures in the form of back surface reflectors (BSR) that increase the optical path length in the thin-film bottom InGaAs subcell to meet the current output realized in their optically thick counterparts. The textured BSR utilizes a facile in situ texturing method to reduce the time and cost of the light-trapping development, suitable for integration into already-established space PV manufacturing. The light current-voltage results on the in situ BSR device show no degradation in the VOC while exhibiting an increased JSC due to the photon scattering. The triple-junction IMM results also show improved current output using the in situ textured BSR compared to a planar mirror geometry. The prediction model in the remaining factor shows the 700 nm-thick devices with the in situ BSR surpasses the optically thick control beyond 1 MeV electrons at a fluence of 2x1014 e-/cm2, which supports the use of the in situ texturing in photovoltaic manufacturing.