Tailoring Molecular Orientation with a Polymer Additive Enables Bilayer Organic Solar Cells with 20.2% Efficiency

Abstract

Tuning the molecular packing from the edge-on to the preferred face-on orientation is beneficial for improving vertical charge transport and the photovoltaic performance in organic solar cells. However, achieving precise control over this structural transition remains a significant challenge due to the complex processing conditions. Herein, a trace amount of the polymer donor PTO2 as an additive, effectively inducing a preferential face-on molecular orientation in the acceptor phase is incorporated. This strategy enhanced exciton dissociation efficiency, improved charge carrier extraction, reduced trap density, and subsequently achieved a fill factor (FF) nearing 80%, results in a power conversion efficiency (PCE) of 20.2%, the highest reported for bilayer OSCs. Remarkably, the PTO2-driven molecular orientation strategy maintains consistent efficacy across diverse donor-acceptor systems, highlighting its broad applicability. This approach offers a comprehensive insight for the effective modulation of NFA molecular orientation, paving a practical approach for high-performance bilayer OSCs.