Hybrid perovskites have emerged as a promising class of materials for light-emitting applications due to their exceptional optoelectronic properties, including high photoluminescence quantum yield (PLQY), tunable emission wavelengths, and narrow emission linewidths. These materials, with the general formula ABX₃, where A is an organic or inorganic cation, B is a metal cation, and X is a halide anion, exhibit strong light-matter interactions and facile processability. Their compositional flexibility allows precise control over optical properties, making them suitable for red, green, and blue emission.

Photoluminescence quantum yield is a critical parameter for light-emitting applications, as it quantifies the efficiency of radiative recombination relative to non-radiative losses. In hybrid perovskites, achieving high PLQY requires minimizing defects and suppressing non-radiative recombination pathways. Compositional engineering plays a key role in this regard. For instance, the introduction of excess organic cations or halides can passivate surface defects, while dimensionality control—such as forming quasi-two-dimensional (quasi-2D) perovskites with large organic spacers—can enhance carrier confinement and reduce trap-assisted recombination. Studies have shown that optimized quasi-2D perovskites can achieve PLQY values exceeding 90% due to efficient exciton funneling to lower-dimensional domains with higher radiative efficiency.

Color purity, characterized by narrow full-width-at-half-maximum (FWHM) values of the emission peak, is another crucial factor for display applications. Hybrid perovskites exhibit intrinsically narrow emission spectra, often with FWHM values below 20 nm, which is superior to many conventional emitters like quantum dots or organic molecules. This narrow emission arises from the direct bandgap nature and strong excitonic effects in these materials. For blue emission, chloride-rich compositions, such as mixed-halide perovskites (e.g., CsPb(Cl/Br)₃), are commonly employed, though achieving stable and efficient blue emission remains challenging due to halide segregation. Green-emitting perovskites, typically based on pure bromide compositions (e.g., CsPbBr₃), exhibit exceptional color purity with FWHM values as low as 15 nm. Red emission is achieved by incorporating iodide (e.g., CsPbI₃ or FAPbI₃), though iodide-based perovskites often require stabilization through compositional tuning or surface passivation to maintain high PLQY.

Stokes shift engineering is essential for reducing reabsorption losses and improving light outcoupling efficiency. The Stokes shift, defined as the energy difference between absorption and emission peaks, can be modulated through compositional and structural modifications. In hybrid perovskites, the intrinsic Stokes shift is typically small due to the direct bandgap nature, but it can be enhanced by introducing exciton localization mechanisms. For example, alloying with smaller cations (e.g., mixing FA⁺ and Cs⁺ in the A-site) can create local lattice distortions that localize excitons and increase the Stokes shift. Similarly, incorporating large organic cations to form low-dimensional perovskites can induce strong exciton-phonon coupling, further broadening the Stokes shift. A carefully engineered Stokes shift is particularly important for applications requiring high color purity and minimal self-absorption, such as in luminescent solar concentrators or high-resolution displays.

Compositional strategies for achieving red, green, and blue emission in hybrid perovskites involve precise control over halide ratios, cation mixing, and dimensionality. For red emission, iodide-dominant compositions like FAPbI₃ or CsPbI₃ are used, but their structural instability at room temperature necessitates stabilization strategies. Incorporating smaller cations like Cs⁺ or Rb⁺ into the A-site can suppress phase transitions, while surface passivation with long-chain ligands enhances environmental stability. Green emission is most reliably achieved with pure bromide compositions like CsPbBr₃ or MAPbBr₃, which exhibit high PLQY and excellent color purity. Blue emission is more challenging due to the tendency of chloride-rich perovskites to form defective phases. Mixed-halide approaches, such as CsPb(Cl/Br)₃, can achieve blue emission, but halide segregation under illumination remains a limitation. Alternatively, reducing the dimensionality by introducing large organic spacers can shift the emission to the blue region while improving stability.

The choice of organic cations also significantly impacts the optoelectronic properties of hybrid perovskites. For example, formamidinium (FA⁺) and methylammonium (MA⁺) are commonly used for their favorable bandgap tunability, but they suffer from thermal and moisture instability. Replacing these with more stable cations like cesium (Cs⁺) or guanidinium (GA⁺) can improve material robustness without compromising optical performance. Additionally, mixed-cation approaches, such as triple-cation compositions (Cs⁺/FA⁺/MA⁺), have been shown to enhance phase stability and PLQY by mitigating lattice strain and defect formation.

Surface chemistry and passivation are equally critical for optimizing light-emitting properties. Long-chain alkylammonium ligands, such as oleylamine or phenethylammonium, can passivate surface traps and suppress non-radiative recombination. In quasi-2D perovskites, the choice of spacer molecules (e.g., butylammonium or octylammonium) influences the energy landscape and exciton dynamics, enabling precise control over emission characteristics.

In summary, hybrid perovskites offer a versatile platform for light-emitting applications, with high PLQY, narrow emission linewidths, and tunable Stokes shifts achievable through compositional and structural engineering. Red emission is stabilized by iodide-rich compositions and cation alloying, green emission benefits from pure bromide systems, and blue emission remains a work in progress with mixed-halide and low-dimensional strategies. Continued advancements in defect passivation, dimensionality control, and cation/halide engineering will further enhance the performance of these materials for next-generation optoelectronic applications.