Characterization of Al2O3 as CIGS surface passivation layer in high-efficiency CIGS solar cells
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
In this thesis, a novel method of reducing the rear surface recombination in copper indium gallium (di) selenide (CIGS) thin film solar cells, using atomic layer deposited (ALD) Al2O3, has been evaluated via qualitative opto-electrical characterization. The idea stems from the silicon (Si) industry, where rear surface passivation layers are used to boost the open-circuit voltage and, hence, the cell efficiency. To enable a qualitative assessment of the passivation effect, Al/Al2O3/CIGS metal-oxide-semiconductor (MOS) devices with 3-50 nm oxide thickness, some post-deposition treated (i.e. annealed), have been fabricated.
Room temperature capacitance-voltage (CV) measurements on the MOS devices indicated a negative fixed charge density (Qf) within the Al2O3 layer, resulting in a reduced CIGS surface recombination due to field effect passivation. After annealing the Al2O3 passivation layers, the field effect passivation appeared to increase due to a more negative Qf. After annealing have also indications of a lower density of interface traps been seen, possibly due to a stronger or activated chemical passivation.
Additionally, the feasibility of using ALD Al2O3 to passivate the surface of CIGS absorber layers has also been demonstrated by room temperature photoluminescence (PL) measurements, where the PL intensity was about 20 times stronger for a structure passivated with 25 nm Al2O3 compared to an unpassivated structure. The strong PL intensity for all passivated devices suggests that both the chemical and field effect passivation were active, also for the passivated as-deposited CIGS absorbers.
Place, publisher, year, edition, pages
2014. , 30 p.
UPTEC ES, ISSN 1650-8300 ; 14030
CIGS, Surface Passivation, Thin Film Solar Cells, Al2O3, Capacitance-Voltage, Photoluminescence
Other Materials Engineering
IdentifiersURN: urn:nbn:se:uu:diva-230228OAI: oai:DiVA.org:uu-230228DiVA: diva2:739332
Master Programme in Energy Systems Engineering
2014-06-19, Uppsala, 10:15 (English)
Jönsson, PetraEdoff, Marika