Ultrafast Photoconductivity and Terahertz Vibrational Dynamics in Double‐Helix SnIP Nanowires

Tin iodide phosphide (SnIP), an inorganic double‐helix material, is a quasi‐1D van der Waals semiconductor that shows promise in photocatalysis and flexible electronics. However, the understanding of the fundamental photophysics and charge transport dynamics of this new material is limited. Here, time‐resolved terahertz (THz) spectroscopy is used to probe the transient photoconductivity of SnIP nanowire films and measure the carrier mobility. With insight into the highly anisotropic electronic structure from quantum chemical calculations, an electron mobility as high as 280 cm2 V−1s−1 along the double‐helix axis and a hole mobility of 238 cm2 V−1 s−1 perpendicular to the double‐helix axis are detected. Additionally, infrared‐active (IR‐active) THz vibrational modes are measured, which shows excellent agreement with first‐principles calculations, and an ultrafast photoexcitation‐induced charge redistribution is observed that reduces the amplitude of a twisting mode of the outer SnI helix on picosecond timescales. Finally, it is shown that the carrier lifetime and mobility are limited by a trap density greater than 1018 cm−3. The results provide insight into the optical excitation and relaxation pathways of SnIP and demonstrate a remarkably high carrier mobility for such a soft and flexible material, suggesting that it could be ideally suited for flexible electronics applications. The ultrafast optoelectronic properties of double‐helix tin iodide phosphide (SnIP) nanowires are explored using time‐resolved terahertz spectroscopy and quantum‐chemical calculations, providing deep insight into their photophysics, carrier dynamics, and anisotropic electronic structure. The carrier mobility is shown to be remarkably high for such a flexible and ultrasoft material, revealing the potential for future applications of SnIP in flexible electronics.