Hydrophobic perovskites based on an alkylamine compound for high efficiency solar cells with improved environmental stability

Abstract

Hybrid quasi-two dimensional perovskites (2D) have attracted significant scientific interest, because they have been demonstrated to be excellent light absorbing materials in photovoltaic devices. However, quasi-2D perovskites still perform poorly in high humidity, even though they have exhibited greatly improved stability compared to their three-dimensional (3D) counterparts. This is the biggest obstacle for the practical implementation and commercial viability of perovskite solar cells. Herein, we used hexylamine (CH₃(CH₂)₄CH₂NH₂, HA) for a quasi-2D, HA(CH₃NH₃)_n−1Pb_nI_3n+1 (n = 1, 2, 3, 4) perovskite, which had sufficiently long alkyl chains to maintain the chemical stability of the perovskite. As the number of layers of quasi 2D HA(CH₃NH₃)_n−1Pb_nI_3n+1 perovskites was increased, they exhibited an appropriate band gap as a light absorber to be applied in solar cells. The perovskite solar cell based on the 2D HA(CH₃NH₃)_n−1Pb_nI_3n+1 perovskites showed an excellent power conversion efficiency of 5.90% with a short circuit current density of 13.61 mA cm⁻¹, an open circuit voltage of 0.72 V, a fill factor of 60.10%, and stability in ambient air. The long alkyl chain of the hexylamine cation prevented the degradation of the solar cell in the atmosphere with passivation of the perovskite films due to their high hydrophobic properties. This investigation highlights the role of the organic cation in maintaining the quality of the perovskite film and provides a critical solution for the poor stability of perovskites in ambient air.