Light absorption enhancement and radiation hardening for triple junction solar cell through bioinspired nanostructures

Abstract

Multi-junction solar cells constitute the main source of power for space applications. However, exposure of solar cells to the space radiation environment significantly degrades their performance across the mission lifetime. Here, we seek to improve the radiation hardness of the triple junction solar cell, GaInP/Ga(In)As/Ge, by decreasing the thickness of the more sensitive middle junction. Thin junctions facilitate the collection of minority carriers and show slower degradation due to defects. However, thinning the junction decreases the absorption, and consequently, the expected photocurrent. To compensate for this loss, we examined two bioinspired surface patterns that exhibit anti-reflective and light-trapping properties: (a) the moth-eye structure which enables vision in poorly illuminated environments and (b) the patterns of the hard cell of a unicellular photosynthetic micro-alga, the diatoms. We parametrize and optimize the biomimetic structures, aiming to maximize the absorbed light by the solar cell while achieving significant reduction in the middle junction thickness. The density of the radiation-induced defects is independent of the junction thickness, as we demonstrate using Monte Carlo simulations, allowing the direct comparison of different combinations of middle junction thicknesses and light trapping structures. We incorporate the radiation effects into the solar cell model as a decrease in minority carrier lifetime and an increase in surface recombination velocity, and we quantify the gain in efficiency for different combinations of junction thickness and the light-trapping structure at equal radiation damage. Solar cells with thin junctions compensated by the light-trapping structures offer a promising approach to improve solar cell radiation hardness and robustness, with up to 2% higher end-of-life efficiency than the commonly used configuration at high radiation exposure.

Biomimetics for innovative and future-oriented space applications - A review

“…Butterfly wings demonstrate periodic nanostructures producing an antireflective effect used to heat their flight muscles, which has been conceptualized and applied as lightweight solar concentrators. Similar nanostructures can also be found in the eyes of moths (Chen et al, 2011(Chen et al, , 2014Shanks et al, 2015;Vasileiou et al, 2021).…”

Ultrathin GaAs solar cells with a high surface roughness GaP layer for light‐trapping application

“…Lowering the thickness can also offer better performance in cells that are grown in ways that do not necessarily ensure high crystalline quality, such as hydride vapor phase epitaxy (HVPE) 1,2 or III‐V on silicon (III‐V/Si), 3 which both have the potential to reduce costs of III‐V cells even further. Ultrathin cells are also less affected by proton and electron radiation induced defects 4–6 and can potentially achieve a higher open‐circuit voltage ( V OC ) than thicker structures 7 …”

“…Lowering the thickness can also offer better performance in cells that are grown in ways that do not necessarily ensure high crystalline quality, such as hydride vapor phase epitaxy (HVPE) 1,2 or III-V on silicon (III-V/Si), 3 which both have the potential to reduce costs of III-V cells even further. Ultrathin cells are also less affected by proton and electron radiation induced defects [4][5][6] and can potentially achieve a higher open-circuit voltage (V OC ) than thicker structures. 7 With a suitable light-trapping scheme increasing the path length through the solar cell, the ultrathin structures can be made optically thick and achieve current-densities matching those of conventional thin film (2-3 μm) GaAs cells.…”