Thermal and Humidity Stability of Mixed Spacer Cations 2D Perovskite Solar Cells

Abstract In this article, two different types of spacer cations, 1,4‐butanediamonium (BDA 2+ ) and 2‐phenylethylammonium (PEA + ) are co‐used to prepare the perovskite precursor solutions with the formula of (BDA) 1‐ a (PEA 2 ) a MA 4 Pb 5 X 16 . By simply mixing the two spacer cations, the self‐assembled polycrystalline films of (BDA) 0.8 (PEA 2 ) 0.2 MA 4 Pb 5 X 16 are obtained, and BDA 2+ is located in the crystal grains and PEA + is distributed on the surface. The films display a small exciton binding energy, uniformly distributed quantum wells and improved carrier transport. Besides, utilizing mixed spacer cations also induces better crystallinity and vertical orientation of 2D perovskite (BDA) 0.8 (PEA 2 ) 0.2 MA 4 Pb 5 X 16 films. Thus, a power conversion efficiency (PCE) of 17.21% is achieved in the optimized perovskite solar cells with the device structure of ITO/PEDOT:PSS/Perovskite/PCBM/BCP/Ag. In addition, the complementary humidity and thermal stability are obtained, which are ascribed to the enhanced interlayer interaction by BDA 2+ and improved moisture resistance by the hydrophobic group of PEA + . The encapsulated devices are retained over 95% or 75% of the initial efficiency after storing 500 h in ambient air under 40 ± 5% relative humidity or 100 h in nitrogen at 60 °C.