Lead halide perovskite solar cells (PSCs) have demonstrated power conversion efficiencies (PCE) up to 25.7%, matching the state-of-the-art silicon solar cells (26.1%). These threedimensional perovskite materials (ABX3) typically include a large cation A + (for example: CH3NH3 + , HC(NH2)2 + or Cs + ), a smaller cation B 2+ such as Ge 2+ , Pb 2+ , Sn , and halide anions X -(for example: I -, Br -, Cl -). The formation of perovskite crystals typically needs to fulfil the Goldschmidt tolerance factor (GTF) defined by the equation 𝐺𝐺𝐺𝐺𝐺𝐺 = (𝑟𝑟 𝐴𝐴 + 𝑟𝑟 𝑋𝑋 )/�(𝑟𝑟 𝐵𝐵 + 𝑟𝑟 𝑋𝑋 ) , where 𝑟𝑟 𝐴𝐴 , 𝑟𝑟 𝐵𝐵, 𝑟𝑟 𝑋𝑋 are the radii of A, B and X ions. A large number of different perovskite materials can be formed based on different permutations of the ionic precursors. Optimization of these precursor ratios has helped to improve the performance as well as stability of these compounds. The latter has to date still proven more challenging due to their sensitivity towards moisture, oxygen, light, temperature and electrical bias, among other factors. Ruddlesden-Popper perovskites (RPPs) are a related material class that has shown some promise to be more resilient to environmental stress then conventional ABX3 perovskites. In this work, we study RPPs with the general formula R2(MA)n-1BnX3n+1, where the R + stands for a large cation(s) which typically does not satisfy the GTF rule, methylammonium cation (MA + ), B 2+ metal cation, and halide anion (X -). The quasi-2D structure of RPPs is shown schematically in Figure . Due to their large size, the R + cation cannot be incorporated into the 3D perovskite lattice.