Two-dimensional halide perovskites have emerged as a “trending topic” low-dimensional semiconductors material in the past decade, for they exhibit a combination of properties – high structure tunability, flexible composition engineering, quantum wells, 2D materials, organic semiconductors, high stability, etc. Its unique structure and property have offered enormous research potential in fundamental physics, material science, chemistry, and photovoltaic device engineering. This thesis aims to explore and develop the synthesis of 2D perovskites, including improving the phase purity of 2D perovskites crystals, realizing the synthesis of 2D perovskite with high perovskite layer-thickness, and inventing novel 2D perovskites with various strategies. Firstly, this thesis addressed a major challenge in the 2D perovskite synthesis which is producing 2D perovskite crystals with desired perovskite-layer thicknesses (quantum well thickness, also known as n values) greater than two. A novel method termed kinetically controlled space confinement (KCSC) for the growth of phase pure 2D perovskites of desired n values for both RP and DJ is introduced. Through this method a transformation from lower n to higher n in 2D perovskites is also demonstrated. Those finding will enable reproducible synthesis of 2D perovskites, specifically for n>4, which is very significant as the higher n 2D perovskites have narrower band gap and higher electrical conductivity, and those parameters are the most crucial factors for application in electronic devices. In the second part, a novel 2D perovskite series with formamidinium (FA) as cage cation is demonstrated. This series of 2D perovskite has the smallest bandgap among all the reported 2D perovskite. Its structure is perfectly linear with no distortion, taking a space group of p4/mmm (tetragonal) which is the maximum symmetry that can be achieved theoretically in 2D perovskite. This novel 2D behaves like a 3D one from all the perspectives, including structure, lattice softness, charge transport. The combination of low band gap with high stability makes it an outstanding candidate for solar cells, both single junction and tandems. Finally, this thesis presents a unique “n=1.5” 2D perovskites, which exhibit an intrinsic multi-layer thickness structure, consisting of alternating n=1 and n=2 layers. This unique structure provides an exciting platform to study the excitons, energy funneling and has huge potential for lasering applications. A new horizon for perovskites research is opened up with a lot of exploration and development on the way.