Two-dimensional cyclohexane methylamine based perovskites as stable light absorbers for solar cells

Two-dimensional Ruddlesden-Popper perovskites (2D-RPPs) have attracted attention due to their superior moisture stability. In this study, we prepared and characterized a new group of 2D perovskites with cyclohexane methylamine (CMA+) as a spacer cation. The compounds (CMA)2(MA)n−1PbnI3n+1 (n = 1, 2, 3, and 4) showed high self-assembly (where MA is CH3NH3), which allowed for high-quality films to be deposited through the one-step spin-coating method in ambient air. Hot-casting technique, additives, and glove box were not required in the fabrication process. The bandgaps of this group of compounds can be varied from 2.36 eV for (CMA)2PbI4 (n = 1) to 1.52 eV for MAPbI3 (n = ∞) with increasing n value. Moreover, we found that the thin films of (CMA)2(MA)n−1PbnI3n+1 showed considerable stability in moisture and thermal tests. We successfully inserted these new 2D-RPPs in solar cells, and obtained the best power conversion efficiency of 10.66%, with an open-circuit voltage (Voc) of 1.00 V, and a short-circuit current density (Jsc) of 16.99 mA/cm2 for our first-generation device containing (CMA)2(MA)3Pb4I13 (n = 4). The CMA-based devices exhibited superior long-term stability, the unencapsulated (CMA)2(MA)3Pb4I13 solar cell retained nearly 95% of its initial efficiency when exposed to ambient conditions with a 60% relative humidity for 1500 h.