Environmental Stability Evaluation of Aluminium Doped Zinc Oxide (AZO) Transparent Electrodes Deposited at Low Temperature for Solar cells

Abstract

The degradation of transparent electrodes’ electrical conductivity under environmental conditions is considered as a major failure mode for solar cells’ long-term efficiency. In this paper, AZO thin films were subjected to the International Electrotechnical Commission (IEC) 61646 test to examine their environmental stability and suitability as front electrodes for solar cells. To explore the interplay between AZO deposition parameters and environmental stability, AZO films were deposited by radio frequency magnetron sputtering at different parameters and without external heating. The conductivity stability evolution upon the testwas investigated via studying the AZO electrical, structural, and morphological characteristics at different deposition conditions. A direct dependence was identified between the samples’ conductivity degradation rates and the samples’ structural and morphological characteristics including grain size, grain boundary density, surface roughness, and compactness. The samples’ resistivity increases linearly over the test period due to both electron density and mobility degradations. Improved stability was observed for thicker AZO samples (360 nm) originating from enhanced grain size, surface profile, and compactness. These samplesmaintained solar cells' applicable sheet resistance of 21.24 Ω/sq (ρ=7.64×10-4 Ω.cm) following the test. The conducted aging studies demonstrated that manipulating the AZO films growth process via optimizing the deposition parameters is an effective pathway for low-temperature deposited electrodes with enhanced environmental stability