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- (PEA₂) MA₄Pb₅X₁₆. 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.