Manipulation of Crystal Orientation and Phase Distribution of Quasi-2D Perovskite through Synergistic Effect of Additive Doping and Spacer Engineering

The diammonium precursor 1,4-phenylenedimethanammonium (PDMA) was used as a large organic spacer for the preparation of Dion-Jacobson-type quasi-2D perovskites (PDMA)(MA)_n−1Pb_nI_3n+1 (MA = methylammonium). Films with composition ⟨n⟩ = 5 comprised randomly orientated grains and multiple microstructural domains with locally differing n values. However, by mixing the Dion-Jacobson-type spacer PDMA and the Ruddlesden-Popper-type spacer propylammonium (PA), the crystal orientation in both the vertical and the horizonal directions became regulated. High crystallinity owing to well-matched interlayer distances was observed. Combining this spacer-engineering approach with the addition of methylammonium chloride (MACl) led to full vertical alignment of the crystal orientation. Moreover, the microstructural domains at the substrate interface changed from low-n (n = 1, 2, 3) to high-n (n = 4, 5), which may be beneficial for hole extraction at the interface between perovskite and hole transport layer due to a more finely tuned band alignment. Our work sheds light on manipulating the crystallization behavior of quasi-2D perovskite and further paves the way for highly stable and efficient perovskite devices.