High-efficiency ITO-free organic solar cells through top illumination

Organic photovoltaics (OPVs) hold great promise for commercialization due to their potential to produce high-performance, and flexible products in a cost-effective and scalable way. Beyond achieving high power conversion efficiency (PCE), the ability to maintain device stability under atmospheric conditions is important for the practical application of flexible OPVs. Our primary objective is to significantly enhance the stability of OPVs by incorporating flexible layers, eliminating unstable materials, and adopting an ITO-free approach. We developed a top-illuminated crumpled OPV architecture by utilizing parylene and Ag layer as the electrode materials. To enhance the PCE of ITO-free OPVs, we have incorporated the electron transport layer, PFN-Br, followed by the deposition of the PM6:Y6 active layer. An intriguing breakthrough emerged in the form of MoO3/Ag/WO3, serving as an innovative transparent electrode and replacing the conventional ITO electrode. The ultimately crumpled OPV exhibited superior PCE and attained a high power-per-weight of 31.07 W g-1. Furthermore, the ITO-free device exhibited excellent stability during dark storage (T95 similar to 1000 hours) and light soaking conditions (T93 similar to 48 hours). Remarkably, even after 48 hours of continuous light soaking, the freestanding crumpled OPVs maintained the PCE at 93% of its initial value, showcasing excellent photostability. Our polymer solar cells boast an extraordinary power-to-weight ratio of 31.07 W g-1. Such devices demonstrate robust photostability, retaining 93% of their initial power conversion efficiency even after 48 hours of continuous light exposure.