Stabilizing wide band gap triple halide perovskite alloy through organic gelators

Engineering the chemical composition of metal-halide perovskites via halide mixing allows a facile bandgap modulation but renders perovskite materials prone to photoinduced halide segregation. Triple-halide alloys containing Cl, I, and Br were recently reported as a means to stabilize Cs(y)FA(1-y)Pb(BrxI1-x)(3) perovskite under illumination. Herein, these triple-halide alloys are found to be intrinsically less stable with respect to the reference I-Br in ambient conditions. By exploiting the influence of low-molecular-weight organic gelators on the crystallization of the perovskite material, a triple-halide alloy with improved moisture tolerance and thermal stability at temperatures as high as 120 degrees C is demonstrated. The hydroxyl-terminated organic gelators are found to aggregate into nanoscale fibers and promote the gelation of the solvent inducing the formation of a 3D network, positively interfering with perovskite solidification. The addition of a tiny amount of organic gelators imparts a more compact morphology, higher crystallinity, and compositional stability to the resulting triple-halide polycrystalline films, making them more robust over time without compromising the photovoltaic performance. Overall, this approach offers a solution toward fabrication of active perovskite materials with higher energy gap and improved stability, making these triple-halide alloys truly exploitable in solar cells.