ABSTRACT
Barrier materials are an important class of materials that have versatile applications. One of the applications is in the field of organic devices. The flexible organic electronics have been an important and interesting research domain for the past few decades. 1–4 Due to the flexibility, lightweight, and the ability to work under diffuse sunlight, organic devices have an exceptional scope for the future. One of the major problems in the introduction of flexible electronics and in particular organic photovoltaic devices commercially in the market is their limited lifetime. This is due to the degradation of the organic conducting polymers (such as polyphenylvinylene) and other small organic molecules leading to device failure (a schematic of an organic photovoltaic device is shown in Figure 24.1), under atmospheric conditions, which is mainly caused by the intrusion of moisture and oxygen into the active device layers. Hence, barrier materials are essential to reduce the exposure of these devices to moisture and oxygen in the atmosphere, which will enhance the lifetime and reduce the degradation of these materials. There are other factors (apart from degradation) contributing to this decrease in efficiency as follows:
Photogenerated excitons that are strongly bound, resisting dissociation into separate charges
Low charge carrier mobility (μ ˜ 10−3–10−5 cm 2 /V s)
Short exciton diffusion length (LD ˜ 5–10 nm)
The deposition of a metal cathode (usually Ag or Al) that can cause defects at the acceptor/cathode interface
The interface stability and physical changes in morphology due to thermodynamic instability
Schematic of degradation in organic devices. PEDOT:PSS, poly(3,4- ethylenedioxythiophene) polystyrene sulfonate; ITO, indium tin oxide. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315371054/19a59aa6-1bb4-4d28-94c7-9f8cac6f3585/content/fig24_1_C.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/>