Metal halide perovskite-based nanostructures, nanosheets and nanoparticles at the forefront, show attractive optoelectronic properties, suitable for photovoltaics and light emission applications. Achieving a sounded understanding of these basic electronic and optical properties represents therefore a crucial step for the full technological exploitation of this class of semiconductors. The rapidly expanding chemical engineering and their unusual structural diversity is fascinating but also challenging for a rational description on par with those well-known for conventional semiconductors. In this sense, group theory-based symmetry analyses offer a general and rigorous approach to understand the properties of various bulk perovskites and perovskite-based nanostructures. In this work, we review the electronic and optical response of metal halide perovskite semiconductors using symmetry analysis from group theory, recalling the main results for the prototypical cubic Pm-3m lattice of AMX₃ bulk perovskites (where A is cation, M metal and X halide), then extending the analysis to three cases of technological interest: AMX₃ nanoparticles, A₄MX₆ isolated octahedra, A₂MX₄ layered systems, and recently introduced deficient halide perovskites (d-HP). On the basis of symmetry arguments, we will stress analogies and differences in the electronic and optical properties of these materials, as induced by the spatial confinement and dimensionality. Meanwhile, we will take advantage of this analysis to discuss recent results and debates from the literature, as the energetics of dark/bright states in the band-edge exciton fine structure of perovskite nanoparticles and nanosheets. From the present work, we also anticipate that the band-edge exciton fine structure of d-HP does not present optically dark states, in striking contrast to AMX₃ nanoparticles and layered perovskites, a fact that can have important consequences on the photophysics of these novel perovskitoids.

基于金属卤化物钙钛矿的纳米结构、纳米片和纳米粒子处于前沿，显示出有吸引力的光电特性，适用于光伏和发光应用。因此，全面了解这些基本的电子和光学特性是对此类半导体进行全面技术开发的关键一步。快速扩展的化学工程及其不寻常的结构多样性令人着迷，但与众所周知的传统半导体一样，对于理性描述来说也具有挑战性。从这个意义上说，基于群论的对称性分析提供了一种通用而严格的方法来理解各种块状钙钛矿和基于钙钛矿的纳米结构的特性。在这项工作中，₃块体钙钛矿（其中 A 是阳离子，M 金属和 X 卤化物），然后将分析扩展到三个具有技术意义的案例：AMX ₃纳米颗粒、A ₄ MX ₆孤立八面体、A ₂ MX ₄分层系统，最近引入了缺陷卤化物钙钛矿（d-HP）。在对称性论证的基础上，我们将强调由空间限制和维度引起的这些材料的电子和光学特性的类比和差异。同时，我们将利用这一分析来讨论最近的结果和文献中的争论，如钙钛矿纳米颗粒和纳米片的带边激子精细结构中暗/亮态的能量学。从目前的工作中，我们还预计 d-HP 的带边激子精细结构不呈现光学暗态，与 AMX ₃纳米颗粒和层状钙钛矿形成鲜明对比，这一事实可能对这些材料的光物理产生重要影响。新型钙钛矿。