Oriented Naphthalene-<i>O</i>-propylammonium-Based (NOP)₄Au<i>B</i>^IIII₈ (<i>B</i> = Au, Bi, Sb) Ruddlesden–Popper Two-Dimensional Gold Double Perovskite Thin Films Featuring High Charge-Carrier Mobility

Two-dimensional perovskites show intriguing optoelectronic properties due to their anisotropic structure and multiple quantum well structure. Here, we report the first three gold-based Ruddlesden-Popper type two-dimensional double perovskites with a general formula (NOP)₄Au^I<i>B</i>^IIII₈ (<i>B</i> = Au, Bi, Sb) employing naphthalene-<i>O</i>-propylammonium (NOP) as an organic cation. They were found to form highly crystalline thin films on various substrates, predominantly oriented in the [001] direction featuring continuous, crack-free film areas on the μm² scale. The thin films show strong optical absorption in the visible region, with band gap energies between 1.48 and 2.32 eV. Density functional theory calculations support the experimentally obtained band gap energies and predict high charge-carrier mobilities and effective charge separation. A comprehensive study with time-resolved microwave conductivity (TRMC) and optical-pump-THz-probe (OPTP) spectroscopy revealed high charge-carrier mobilities for lead-free two-dimensional perovskites of 4.0 ± 0.2 cm²(V s)^-1 and charge-carrier lifetimes in the range of μs. Photoconductivity measurements under 1 sun illumination demonstrated the material's application as a photodetector, showing a 2-fold increase in conductivity when exposed to light.