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

In this article, two different types of spacer cations, 1,4‐butanediamonium (BDA2+) and 2‐phenylethylammonium (PEA+) are co‐used to prepare the perovskite precursor solutions with the formula of (BDA)1‐a(PEA2)aMA4Pb5X16. By simply mixing the two spacer cations, the self‐assembled polycrystalline films of (BDA)0.8(PEA2)0.2MA4Pb5X16 are obtained, and BDA2+ 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(PEA2)0.2MA4Pb5X16 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 BDA2+ 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. In this work, the mixed spacer cations 2D perovskite (BDA)0.8(PEA2)0.2MA4Pb5X16 films are obtained by employing two typical spacer cations, 1,4‐butanediamonium (BDA2+) usually for Dion‐Jacobson phase and 2‐phenylethylammonium (PEA+) for Ruddlesden‐Popper phase. The device with (BDA)0.8(PEA2)0.2MA4Pb5X16 film achieves the power conversion efficiency of 17.21% with excellent thermal and humidity stability.