| AVS 66th International Symposium & Exhibition | |
| Thin Films Division | Thursday Sessions |
| Session TF+EM+NS+SS-ThM |
| Session: | Thin Films for Energy Harvesting and Conversion |
| Presenter: | Erin Cleveland, U.S. Naval Research Laboratory |
| Authors: | E. Cleveland, U.S. Naval Research Laboratory N.A. Kotulak, U.S. Naval Research Laboratory S. Tomasulo, U.S. Naval Research Laboratory P. Jenkins, U.S. Naval Research Laboratory A. Mellor, Imperial College London, UK P. Pearce, Imperial College London, UK N.J. Ekins-Daukes, University of New South Wales, Australia M.K. Yakes, U.S. Naval Research Laboratory |
| Correspondent: | Click to Email |
In space applications, a key figure of merit is conversion efficiency at end-of-life, which combines both beginning–of-life efficiency with degradation due to radiation exposure on orbit. In currently used InGaP/GaAs/Ge triple junctions, the GaAs middle cell has the most pronounced degradation, which limits the total current generation at the end-of-life. Recently, we demonstrated that as the thickness of the GaAs cell decreases, the tolerance to radiation damage increases. [1] However, because the cell absorbs less light as the thickness of the active region is reduced, the beginning-of-life performance suffers as compared to optically thick cells. To realize the benefits of both structures, light trapping architectures may be used to increase absorption within the cell while still maintaining the increased radiation tolerance of the thinner geometry.
Designing a wavelength selective light trapping structure positioned interstitially between two of the subcells of a multi-junction device is a new challenge which prohibits many of the well-known light trapping techniques. Recently, we have proposed a structure which combines a distributed Bragg reflector (DBR) with a textured diffraction grating. [2] Such a structure would provide substantial absorption of light in the middle subcell of a multi-junction device, while still allowing enough low-energy light to pass through the structure so the bottom cell remains well current matched with the other junctions. This structure is proposed to have over an order of magnitude increase in overall radiation tolerance while maintaining comparable beginning of life performance to the current technology.
In this presentation, we present a first experimental demonstration of this structure. The design combines a diffraction grating fabricated via nanosphere natural lithography [3], a low-index transparent spacer layer, and a DBR, which synergistically traps light inside the targeted subcell. This presentation will highlight processing techniques and challenges associated with fabricating a textured ultra-thin solar cell, while illustrating the effectiveness of integrating light trapping structures within an ultra-thin solar cell as an effort towards realizing high efficiency ultra-thin photovoltaic devices.
[1] L. C. Hirst, et.al, “Intrinsic radiation tolerance of ultra-thin GaAs solar cells”, APL, 109 (2016)
[2] A. Mellor, N.P. Hylton, S.A. Maier, N. Ekins-Daukes, “Interstitial light-trapping design for multi-junction solar cells”, Solar Energy Materials & Solar Cells, 159, (2017)
[3] H.W. Deckman and J.H. Dunsmuir, “Natural lithography”, Applied Physics Letters, 41(4) (1982)