Relieving strain on silver nanowires embedded in polyimide films for efficient flexible organic photovoltaic modules

Abstract

Embedding silver nanowires (AgNWs) into polymer substrates is an effective strategy for achieving highly efficient transparent electrodes. However, scaling up the embedded electrode from small areas to a large scale remains challenging, as the strain induced during the drying process of the polymer substrate deteriorates conductance. In this work, we report that the thick PI coating on AgNWs generates strain during the drying process, which negatively impacts the conductance of the electrode. To verify this phenomenon, we propose a two-step coating PI method. Specifically, a thin PI layer was initially coated on the AgNWs to minimize strain during the drying process, followed by the deposition of a thick PI layer to achieve the desired film thickness. Ultra-thin parylene was deposited between the thick and thin PI layers ensuring that the thick PI layer does not affect the AgNW electrode. We chose the way of decreasing the thickness of PI to relieve the strain on the fabricated electrode. With the smooth, flexible and transparent electrode of AgNWs embedded into PI substrates (denoted as AgNWs-em-PI), flexible organic photovoltaic cells and modules were successfully fabricated. Small-area (0.04 cm²) flexible cells displayed a power conversion efficiency (PCE) of 15.12%, and flexible large area modules (11.57 cm²) further achieved a PCE of 14.21%. This represents the first demonstration of organic photovoltaic modules with the AgNW electrode and polyimide substrates.