AVS 66th International Symposium & Exhibition
    Fundamental Aspects of Material Degradation Focus Topic Thursday Sessions
       Session DM2+BI+SS-ThA

Paper DM2+BI+SS-ThA11
Stabilizing Transparent Conductive Oxides as a Route to Long-Lived Thin Film Photovoltaics: A Case Study in CIGS

Thursday, October 24, 2019, 5:40 pm, Room A212

Session: Fundamentals of Catalyst Degradation: Dissolution, Oxidation and Sintering
Presenter: Ina Martin, Case Western Reserve University
Authors: N.C. Kovach, Colorado School of Mines
R. Matthews, Case Western Reserve University
E.B. Pentzer, Case Western Reserve University
L. Mansfield, National Renewable Energy Laboratory
T.J. Peshek, NASA Glenn Research Center
I.T. Martin, Case Western Reserve University
Correspondent: Click to Email
Degradation of the aluminum-doped zinc oxide (AZO) top contact is a known failure mode in Cu(In,Ga)Se2 (CIGS) solar cells. The degradation of the AZO can be observed in device and module current-voltage characteristics as an increase in series resistance and decrease in fill factor. Due to its low cost and earth abundance, AZO is a good choice for the TCO in thin-film solar cells. However, it has one of the higher degradation rates of TCOs under damp heat stress. 3-aminopropyltriethoxysilane (APTES) was used to modify the AZO top contacts in CIGS solar cells. Results demonstrate that the application of the nm-scale modifier mitigates AZO degradation in damp-heat exposure, and further, arrests the degradation of the full CIGS device.

APTES modification of thick (~0.8 μm) AZO films significantly impedes the electrical degradation of the material caused by DH exposure, without significantly affecting the initial optical, electrical, or structural properties of the AZO films. Upon 1000 h of DH exposure, resistivity of both systems increased and can be attributed only to decreased mobility, as carrier concentration was consistent. APTES modification slowed the increase in AZO resistivity over 1000 h of DH exposure; however, the protective nature of APTES modification became critical after 1500 h. At this extended exposure time, macroscopic degradation was observed only for bare AZO including pitting and delamination and was accompanied by an increase in resistivity and decrease in carrier concentration. X-ray photoelectron spectroscopy (XPS) data show that the APTES layer stabilizes the oxygen binding environment of the AZO surface, suggesting that covalent passivation of AZO surface sites by silanization essentially “caps” reactive moieties, thereby improving the stability of the material.