Stabilization of 3-D trigonal phase in guanidinium (C(NH₂)₃) lead triiodide (GAPbI₃) films

An understanding of the phase transition in organic-inorganic hybrid perovskites is quite important. These phase transitions have been widely studied as they induce differences in structural, electronic, and optical properties. Thermochromic perovskite materials, which alter their optical bandgap in response to a change in temperature, have shown their potential in smart photovoltaic window applications by utilizing the structural phase transitions of inorganic halide perovskites. Here, we investigated the thermochromic properties of guanidinium (C(NH₂)₃) lead triiodide (GAPbI₃) which shows a reversible crystallographic phase transition between a transparent orthorhombic phase (Pna2₁) (<160 °C) and a yellow-colored trigonal phase (R3¯m) (>160 °C). The thermal behavior, crystallographic information, and optical and electronic properties of GAPbI₃ in these two phases were also investigated. We are the first to report that an atomic layer deposition (ALD)-grown SnO₂ passivation layer deposited on top of the perovskite layer can successfully stabilize trigonal-phase of GAPbI₃ for 14 h. Furthermore, in the GAPbI₃ photodetector device, the on/off photoswitching property was greatly enhanced through thermochromism.