PhPAPy is a self-assembled monolayer material featuring a rigid aromatic ring structure with a pyrene terminal, a phenyl linker and a phosphonic anchor. Sandwiched between the substrate and the perovskite active layer, PhPAPy monolayer serves as the hole selection layer (HSL) for high efficiency inverted perovskite solar cells. The rigidity presented by the pyrene terminal hinders rotational freedom thus creates a near-vertical molecular orientation on the substrate. Also, the planar pyrene structure and the near-vertical molecular orientation enhance π–π interactions between the pyrene rings, giving an orderly and densely packed self-assembled monolayer. This uniform film geometry effectively enhances the interfacial properties, minimizes the direct contact between the active layer and the substrate, and reduces buried interface defects for efficient hole extraction to improve both efficiency and stability.
As a result, inverted PSCs based on PhPAPy as the HSL demonstrate a maximum reverse-scanning power conversion efficiency (PCE) of 26.74% and a certified stabilized power output efficiency of 26.12%. Moreover, 95% of their initial efficiency is retained after 2000 h of maximum power point tracking under continuous AM 1.5G illumination at 65 °C and ambient humidity (ISOS-L-2).
PhPAPy has the same terminal group as Py3, another pyrene based self-assembled monolayer material for high-efficiency PSCs.
Serving as hole selective contact for organic solar cells and perovskite solar cells, PhPAPy is an alternative to PEDOT:PSS with superior performance and the convenience of solution deposition at low concentration, i.e. 1 mM.