Strength of attraction: pyrene-based hole-transport materials with effective π–π stacking for dopant-free perovskite solar cells

Currently, organic small molecules represent a widely used class of hole-transport layer (HTL) materials in perovskite solar cells (PSCs). Commonly, these materials are doped to compensate for their low hole-mobility, which leads to an additional increase of the device cost along with the stability issues. An alternative approach is to use compounds containing large aromatic moieties, which can interact within the film at the intermolecular level, improving its conductivity. To demonstrate this strategy, we present four pyrene derivatives as HTL materials for perovskite solar cells. It is shown that devices fabricated using thermally evaporated films of pyrene derivatives deliver superior performance as compared to the cells with solution-processed HTLs. The power conversion efficiency of 17.9% is achieved for dopant-free perovskite solar cells using pyrene-based HTL with α-naphthylamine substituents.