Berlin 2018 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 6: Photovoltaics I
HL 6.11: Talk
Monday, March 12, 2018, 12:15–12:30, EW 203
Aluminum oxide passivation layers for Cu(In,Ga)Se2 thin-film solar cells — •Florian Werner1, Conrad Spindler1, Susanne Siebentritt1, Dimitri Zielke2, and Jan Schmidt2 — 1Laboratory for Photovoltaics, Physics and Materials Science Research Unit, University of Luxembourg, L-4422 Belvaux, Luxembourg — 2Institute for Solar Energy Research Hamelin (ISFH), Am Ohrberg 1, D-31860 Emmerthal, Germany
We employ ac and dc electrical measurements and photoluminescence to investigate the growth and passivation performance of aluminum oxide layers deposited by plasma-assisted atomic layer deposition (ALD) on Cu(In,Ga)Se2. Already few monolayers of aluminum oxide hinder current flow through the device and result in non-linear current-voltage characteristics, which scale with the nominal thickness of the passivation layer. This indicates that a compact insulating layer is formed already after a few ALD cycles despite the larger surface roughness and different surface chemistry compared to standard single-crystalline silicon. Using plasma-assisted ALD, as-deposited aluminum oxide layers do not provide any meaningful surface passivation. Annealing for several minutes even at moderate temperatures of 350 °C results in a drastic improvement of the effective carrier lifetime, resulting in a level of surface passivation comparable to optimized CdS buffer layers. For such moderate annealing conditions we do not observe any indication of the formation of negative fixed charges, which would suppress interface recombination even further. A higher thermal budget, however, has so far led to a degradation of the passivated devices.