Thin Film Encapsulation of Organic Solar Cells by Direct Deposition of Polysilazanes from Solution

Abstract

Organic electronic devices (OEDs), e.g., organic solar cells, degrade quickly in the presence of ambient gases, such as water vapor and oxygen. Thus, in order to extend the lifetime of flexible OEDs, they have to be protected by encapsulation. A solution‐based encapsulation method is developed, which allows the direct deposition of the diffusion barrier on top of OEDs, thus avoiding lamination of barrier films. The method is based on the deposition of a perhydropolysilazane (PHPS) ink and its subsequent conversion into a silica layer by deep UV irradiation. The resulting barrier films show water vapor transmission rates (WVTRs) of <10−2 g m−2 d−1 (40 °C/85% relative humidity (RH)) and oxygen transmission rates (OTRs) of <10−2 cm3 m−2 d−1 bar−1 at ambient conditions. Flexibility of the resulting barrier films is improved by coating a barrier stack of several thin PHPS layers alternating with organic polymer interlayers. These stacks show an increase of WVTR values by less than 10% after 3000 bending cycles. Direct coating of the PHPS films on top of organic solar cells enhances the device lifetime in damp heat conditions from a few hours to beyond 300 h.

Solution Processed PVB/Mica Flake Coatings for the Encapsulation of Organic Solar Cells

“…Most of the active materials used in organic solar cells degrade due to reactions of oxygen and moisture [ 1 , 2 , 3 ]. To reduce this degradation, the process of encapsulation is carried out for the protection of devices [ 4 ]. The quality of the barrier materials determines the life of organic electronic devices [ 5 , 6 ].…”

“…For instance, a short-term protection of devices between production and final encapsulation. Therefore, barrier films exhibiting oxygen and moisture permeabilities of ~0.12 cm⋅cm 3 ⋅m −2 ⋅day −1 ⋅bar −1 and ~0.05 cm⋅g⋅m −2 ⋅day −1 , respectively, can be used for the temporary protection of solar cell devices [ 4 ]. Additionally, encapsulation as a protective layer should not disturb the basic characteristics of devices.…”

Flexible Transparent Barrier Applications of Oxide Thin Films Prepared by Photochemical Conversion at Low Temperature and Ambient Pressure

“…An interesting alternative to the production of barrier foils for encapsulation of electronic devices is the direct application of PHPS solutions on device stacks like organic solar cells (Channa et al, 2019) followed by VUV-induced conversion to SiO 2 . In order to prevent VUV-induced degradation of the underlying photo-active film and to reduce mechanical stress, a protective bi-layer comprising a ZnO-nanoparticle thin film and a UVcurable acrylic resin interlayer were introduced on top of the P3HT film.…”

“…In the case of B2B two hydrophobic surfaces have to be laminated whereas the F2B case requires lamination of different surfaces. Mechanical decoupling of several brittle inorganic thin films allows lower bending radii and have been shown to exhibit long term bending stability; only a moderate increase of WVTR values by less than 10% was observed after 3,000 bending cycles (Channa et al, 2019). The position of the gas barrier film within the functional film stack becomes crucial for bending stability of optoelectronic devices.…”

Tackling Performance Challenges in Organic Photovoltaics: An Overview about Compatibilizers

“…Environmental stressors such as oxygen, moisture, heat, and UV radiation can induce significant degradation effects in OSCs. Strategies such as encapsulation can mitigate these parasite processes through protection from external stimuli [60] but cannot shield from intrinsic phenomena, such as interdiffusion between constituent materials and temporal changes in the nanoscale morphology of the active layer. Inherent instability can be tackled in some ways via careful component choice and/or through morphology control strategies [61].…”