Low-damage encapsulation of flexible organic photovoltaic modules using alternating organic and inorganic layers

Abstract

Effective encapsulation of flexible large-area organic photovoltaic (OPV) modules to prevent water and oxygen penetration remains a critical challenge. In this work, we report the encapsulation of flexible OPV modules by depositing alternating parylene (5 μm) and alumina (Al₂O₃, 25 nm) dyads via chemical vapor deposition (CVD) and atomic layer deposition (ALD), respectively. The deposition temperature of the encapsulation film is important for minimizing the efficiency loss during the encapsulation process. Deposition temperatures over 100 °C for ALD Al₂O₃ films would cause a decrease in the efficiency of OPV devices. To balance the efficiency and encapsulation performance, we employed a strategy of increasing the purge time of trimethylaluminum and water at a lower temperature (60 °C) for ALD Al₂O₃ deposition. This approach achieved similarly low water vapor transmission rates (WVTRs) to those deposited at higher temperatures with short purge times. As a result, the fabricated encapsulation film (parylene/Al₂O₃/parylene) achieved a low WVTR of 1.7 × 10⁻⁴ g m⁻² day⁻¹ (tested at 85 °C and 85% RH), where Al₂O₃ was deposited at 60 °C with a purge time of 30 s. The encapsulated flexible OPV modules could retain 90% of the initial efficiency over 1000 h under continuous illumination (100 mW cm⁻², white LED, 40 °C, 70% RH).