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 degrees C.

Automated summary

By using two different types of spacer cations to prepare perovskite precursor solutions, self-assembled polycrystalline films with improved crystallinity and vertical orientation are obtained, leading to a high power conversion efficiency in solar cells. The mixed spacer cations also enhance interlayer interaction and moisture resistance, resulting in excellent humidity and thermal stability of the devices.