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

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.