Researchers at EPFL's Laboratory for Molecular Engineering of Optoelectronic Nanomaterials (LIMNO) and the University of Bern have designed an organic spacer molecule that turns the normally optically inactive layer of a 2D perovskite into a light-absorbing part of the device itself. Layered "2D" perovskites are built from alternating organic and inorganic layers and are valued for their improved environmental stability and suppressed ion migration compared to standard 3D perovskites. However, the organic spacer molecules conventionally used to separate the inorganic layers, such as phenethylammonium (PEA), neither absorb sunlight nor conduct charge well, which limits both light harvesting and device performance. The team addressed this by building a spacer cation around a diketopyrrolopyrrole (DPP) core, an organic semiconductor known for strong absorption deep into the visible spectrum. By systematically tuning the length of the alkyl chain linking the DPP core, the researchers found that a dihexyl-substituted version was the right size to form an ordered layered perovskite structure, denoted (DPP-dH)PbI 4 , while shorter linkers produced only disordered, amorphous material.