Degradation of transparent conductive oxides; Mechanistic insights across configurations and exposures

Understanding transparent conductive oxide (TCO) degradation is critical to improving stability and lifetime of both organic and inorganic thin fi lm PV modules, which utilize TCOs, like indium tin oxide (ITO), aluminumdoped zinc oxide (AZO) and fluorine-doped tin oxide (FTO) as electrodes. These TCOs must retain their long-term functionality in diverse outdoor environments. In addition to bulk material degradation, interfacial degradation, a frequent avenue for failure in PV systems, is promoted by exposure to environmental stressors such as irradiance, heat and humidity. ITO, AZO and FTO samples in an open-faced con fi guration were exposed to damp heat and ASTM G154 for up to 1000 hours. The e ff ect of exposure on electrical and optical properties and surface energies of cleaned samples was measured. Yellowness, haze, water contact angle and resistivity of the di ff erent materials trended di ff erently with exposure time and type, indicating the activation of distinct degradation mechanisms. An encapsulated con fi guration study was conducted on ITO and AZO, exposing samples to the above accelerated exposures and two outdoor exposures (1x suns and 5x suns on a dual axis trackers), with and without PEDOT: PSS layers. PEDOT: PSS increases the yellowness and haze of ITO and AZO, but does not accelerate the increase in resistivity, suggesting that the optical and electrical degradation mechanisms are not coupled. Additionally, the hazing/ roughening mechanism of PEDOT: PSS on AZO appears to be photo-sensitive; 5x outdoor exposure samples demonstrated distinctly higher haze than damp heat exposed samples.