Metal halide perovskites (MHPs) have become the preeminent semiconducting materials serving for photovoltaics, light-emitting diodes, photodetectors, lasers and photocatalysis, attributed to their superior optoelectronic properties. Low-dimensional MHPs with unique properties originating from quantum confinement and dimension dependence have garnered considerable attention in photonic and electronic studies. To enrich the function versatility and performance optimization to address the practical challenges, chemical engineering strategies have been applied in MHPs including compositional modification, heterostructure fabrication, and composite synthesis. This thesis will center on the compositional and heterostructure engineering in low-dimensional MHPs, specifically lead-free bismuth halide perovskites, for the unprecedented MHP research on photonics, spin physics and energy conversion. First, chemical vapor deposition and anion exchange protocols to synthesize bismuth halide perovskite nanoflakes with controlled dimensions and variable compositions are established. In particular, the gradient bromide distribution by controlling the anion exchange and diffusion is spatially resolved by the time-of-flight secondary ion mass spectrometry. Moreover, the optical waveguiding properties of bismuth halide perovskites can be modulated by the flake thickness and anion composition. Next, a novel metal ion doping protocol through the vapor phase metal halide insertion reaction to the CVD-grown ultrathin Cs3BiBr6 perovskites is presented. The Fe-doped Cs3BiBr6 (Fe: Cs3BiBr6) II perovskites demonstrate that the iron spins are successfully incorporated into the lattice, as revealed by the spin-phonon coupling below the critical temperature Tc around 50 K observed through the temperature-dependent Raman spectroscopy. Furthermore, the phonons exhibit significant softening under the applied magnetic field, possibly originating from magnetostriction and spin exchange interaction. In addition to the compositional engineering in ultrathin bismuth halide perovskite crystals, the direct CVD growth of the Cs3Bi2I9 based heterostructures is introduced. Cs3Bi2I9-MoSe2 and Cs3Bi2I9-MoS2 heterostructures are synthesized to investigate the strong interlayer couplings within the heterostructures. Cs3Bi2I9-graphene heterostructures are developed for future applications in X-ray sensing transistors. Finally, the synthesis of lead-free bismuth halide perovskite nanocrystals encapsulated by the covalent organic frameworks (PNCs- COFs) via an in-situ growth approach is reported. The PNCs-COFs were further applied as photocatalysts for free-radical polymerizations, photo-activating different co-initiators via both hole and electron transfer mechanisms in aqueous and organic phases. The excellent photocatalytic performance of PNCs-COFs was confirmed by high monomer conversion (up to 97.5%), diverse functional group tolerance and recyclability. These protocols provide facile, universal, well-adaptable and efficient avenues for exploring the versatilities of Bi-based perovskite materials in low dimensions. The endeavors devote to shedding light on the potential of low-dimensional MHPs (bismuth halide perovskites) as promising semiconductors for optoelectronics, spin physics and solar energy harvesting.