Solvent engineering for two-dimensional perovskite of guanidium lead iodide

Abstract

Guanidinium lead tri-iodide-based perovskite (GAPbI(3)) is considered a potential candidate for stable structural template of future perovskite solar cells (PSCs) due to the high molecular symmetry of the GA cation, leading to a near-zero dipole moment, along with a high thermodynamic stability. However, a very low power conversion efficiency (PCE) has been reported for GAPbI(3) PSC due to its low-dimensionality, comparatively large band gap, and significant trap states due to large grain boundaries and severe aggregation. In the present study, a two-dimensional (2D) GA(2)PbI(4) perovskite is prepared via a one-step Lewis acid-base adduct approach in which a 7:3 ratio of 4-tert-butylpyridine (tBP) and thiourea in dimethylformamide is employed as the Lewis base. It is observed that the tBP promotes the layer-by-layer growth of 2D perovskite in two directions by guiding multiple PbI2 layers more effectively. The optimized GA(2)PbI(4) perovskite film exhibits better uniformity, large grain size, reduced trap states, and a lower band gap of 2.03 eV. The device containing the GA(2)PbI(4) perovskite exhibits a PCE of ca. 1.74%, along with long-term durability under ambient conditions, and hysteresis-free current density -voltage behavior. The significant enhancement in the PCE of the GA cation-based PSC leaves scope for further improvement in the perovskite-based devices.