From 20% single-junction organic photovoltaics to 26% perovskite/organic tandem solar cells: self-assembled hole transport molecules matter

Achieving high efficiency in single-junction organic solar cells (OSCs) and tandem solar cells (TSCs) significantly relies on hole transport layers constructed from self-assembled molecules (SAMs) with a well-ordered, face-on alignment. In this study, we enhanced the ordered stacking of a SAM layer by leveraging the interaction between the π-conjugated backbone of SAMs and volatile solid additives with opposing electrostatic potentials. This approach induced a highly ordered stacking of the SAM layer, as confirmed by the presence of multiple X-ray scattering peaks and an increased Herman orientation factor from 0.402 to 0.726 after the evaporation of solid additives. This optimization not only strengthened hole transport properties but also positively influenced the film formation kinetics of the upper active layer, improving morphology and vertical phase separation. As a result, we achieved a notable power conversion efficiency (PCE) of 20.06% (certified 19.24%) in PM6:BTP-eC9 binary OSCs, with a further breakthrough PCE of 26.09% in perovskite-organic tandem solar cells (TSCs).