Diketopyrrolopyrrole‐Based Cation as a Semiconducting Spacer in Layered Perovskite

ABSTRACT

Incorporating π‐conjugated organic spacers in layered “2D” perovskites in order to extend solar light harvesting has remained a challenge, as typically‐incorporated spacers (e.g. phenethylammonium, PEA ⁺ ) do not absorb deep into the visible spectrum. Here, we introduce a visible‐light‐absorbing π‐conjugated dithiophene–diketopyrrolopyrrole‐based spacer cation that forms a pure iodide layered perovskite that exhibits complementary organic–inorganic absorption and a type‐II nano‐heterojunction electronic structure. By chain length engineering, a dihexyl‐substituted diketopyrrolopyrrole cation (DPP‐dH ²⁺ ) is identified as the optimal length required to form an ordered layered structure (DPP‐dH)PbI ₄ . Transient absorption spectroscopy reveals bidirectional charge transfer, with hole transfer from the inorganic [PbI ₄ ] ²⁻ slabs to the organic spacer, and electron transfer in the reverse direction upon excitation at longer wavelengths. Time‐resolved microwave conductivity and space‐charge‐limited current measurements demonstrate reduced trap density and electron mobilities up to 1.3 × 10 ⁻³ cm ² V ⁻¹ s ⁻¹ . Leveraging its extended visible absorption, the resulting layered perovskite exhibits a marked improvement in photovoltaic power conversion efficiency compared to (PEA) ₂ PbI ₄ as well as an extended incident photon harvesting reaching 650 nm (1.9 eV), establishing diketopyrrolopyrrole spacers as a promising platform for next‐generation optoelectronics.