Optical properties of thin film solar cell structures on imprinted microstructures

Whelan, Patrick Rebsdorf

4. term

Nanotechnology, Master

2013

2013-06-07

98 pages

Effektive metoder til at indfange lys er påkrævet for tyndfilmssolceller baseret på amorft silicium grundet solcellens reducerede tykkelse. Antireflektive coatinger kan reducere reflektionen fra overfladen, men det har vist sig mere effektivt for et større bølgelængdeinterval at mikrostrukturere solcellens overflade. Dette projekt beskriver, hvordan mikrostrukturer kan imprintes i plexiglass. Anvendelsen af plexiglass i designet af en tyndfilmssolcelle tilfører styrke og lettere håndtering. Processen, der præsenteres i dette projekt, vurderes at kunne anvendes til produktion i større skala. Fem forskellige grundlæggende strukturer var fremstillet til at imprinte i plexiglass. Fire af strukturerne blev fremstillet ved anodisering af aluminum i forskellige syrer, mens den femte struktur blev lavet ved hjælp af anisotropisk ætsning i krystallinsk silicium. Lag af indium-tin-oxid, amorft silicium og aluminium blev tilført de imprintede overfalder for at efterligne en solcelle. Reflektionen og transmissionen fra overfladerne blev målt, og overfladerne blev kortlagt ved AFM og SEM for at kunne modellere overfladerne. Modellerne af overfladerne blev brugt til at simulere de optiske egenskaber ved hjælp af Lumerical FDTD Solutions . Det blev vist ud fra reflektionsmålingerne, at reflektionen af det indfaldende solspektrum kunne reduceres til 13.1% for imprint med 300 nm a-Si og Al i forhold til en reflektion på 46.7% for en flad overflade med de samme lag. Ved at tilføre et lag af antireflektiv coating kunne reflektionen reduceres yderligere til ~9%.

Thin film solar cells based on amorphous silicon require efficient light trapping due to the reduced thickness of the cell. Antireflective coatings may reduce the reflectance, but microstructuring the surface has been shown to be more efficient for a broader wavelength range. In this project, structured PMMA substrates were prepared by a micro-imprinting process. Using PMMA in the solar cell design adds strength to a thin film solar cell and provides easy handling. The process presented here is deemed viable for larger scale production. Five different masters were used for obtaining microstructured PMMA substrates. Four masters were synthesized by anodic anodization of aluminum and the fifth master was prepared by anisotropic etching in crystalline silicon. Indium tin oxide, amorphous silicon and aluminum layers were deposited on the imprinted surfaces in order to imitate a solar cell structure. Reflection and transmission measurements were conducted and the surfaces were examined by AFM and SEM in order to model the surfaces. The surface models were used for simulating the optical properties with Lumerical FDTD Solutions . Based on the reflection measurements, it was shown that the reflection of the AM1.5 solar spectrum could be lowered to 13.1% for imprints with 300 nm a-Si and Al compared to a planar surface with similar layers that reflect 46.7% of the incident solar spectrum. The reflection could be lowered further to ~9% by adding an antireflective ITO layer.

Solcelller ; Nanoteknologi

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