Harnessing Pb–S Interactions for Long‐Term Water Stability in Cesium Lead Halide Perovskite Nanocrystals

Interfaces between nanocrystals and their stabilizing ligands in light‐harvesting devices are crucial for mediating energy transfer, essential for efficient solar energy conversion. In metal halide perovskites, a promising material for these devices, Förster resonance energy transfer (FRET) within perovskite/acceptor‐molecule complexes offers a pathway for optimized energy transfer. However, traditional methods for optimizing FRET in perovskite‐chromophore hybrids are based on static modifications. This study presents an innovative approach for light‐driven dynamic control of FRET, achieving an ≈14% enhancement in efficiency between CsPbBr3 nanocrystals (CPB NCs) and rhodamine B isothiocyanate (RITC) dye. UV light is utilized to reversibly regulate NC‐ligand binding and thus control the coupling between CPB NCs and RITC at their interface. This approach critically relies on strong NC–ligand interactions, such as the Pb─S bond between CPB NCs and RITC. Light exposure weakens the binding of surface ligands, allowing RITC, with its strong bond, to attach more effectively and promote enhanced energy transfer. This light‐activated control is absent with Rhodamine B (RhB) lacking ─NCS group, a strong binding motif. The findings reveal the importance of NC–ligand interactions in dynamically manipulating FRET with light. This pioneering method for nanoscale FRET control paves the way for more efficient light‐harvesting devices.

Unlocking Enhanced Light Harvesting in Perovskites: A Light‐Mediated Ligand Management Approach

Singh,

Ganguly,

Aggarwal

et al. 2024

Leveraging Phenazine‐Based Ligands for Optimized Perovskite Optoelectronic Performance Through Chelation and Redox Engineering

Aggarwal,

Chaudhary,

Singh

et al. 2024

Perovskite nanocrystals (PNCs) hold immense potential for optoelectronic and photovoltaic applications. However, their performance is hindered by surface defects that promote non‐radiative recombination and reduce stability. Surface engineering, particularly through defect passivation, is crucial for achieving high‐performing perovskite solar cells. Chelation has been shown to significantly improve the efficiency and stability of perovskite solar cells. In this study, a novel chelation strategy using 1,10‐Phenanthroline (Phen) is presented as a bidentate chelating ligand to effectively target and passivate these detrimental surface defects. By strategically designing a Phenanthroline derivative, dipyrido[3,2‐a:2′,3′‐c]phenazin‐11‐amine (Phen‐derivative) with optimized redox potentials, dual functionality: efficient defect passivation and hole transport is achieved. X‐ray photoelectron spectroscopy (XPS) confirms the superior binding capability of the Phen‐derivative due to chelation. This strong interaction facilitates efficient and ultrafast charge transfer from PNCs and the formation of a long‐lived charge‐separated state, as evidenced by sustained bleaching in transient absorption spectra. A metal‐dipyrido[3,2‐a:2′,3′‐c]phenazin‐11‐amine complex (Ir‐complex) derived from dipyrido[3,2‐a:2′,3′‐c]phenazin‐11‐amine, but lacking a chelation site, hinders desired hole transfer despite similar charge transfer energetics. This work emphasizes the critical role of chelation‐mediated interfacial interactions and energy alignment in designing effective charge shuttle molecules and unlocking the potential of lead‐chelating hole transporters for next‐generation light‐harvesting technologies.

Mapping Binding Sites for Efficient Hole Extraction in Lead Halide Perovskites through Sulfur‐Based Ligand Engineering

De,

Singh,

Aggarwal

et al. 2024

Lead halide perovskite nanocrystals (NCs) rapidly emerge as promising materials for photovoltaics. However, to fully harness their potential, efficient charge extraction is crucial. Despite rapid advancements, the specific active sites where acceptor molecules interact remain inadequately understood. Surface chemistry and interfacial properties are pivotal, as they directly impact charge transfer efficiency and overall device performance. This study identifies and maps binding sites for hole transporters, examining their influence on charge transfer dynamics through ligand engineering with 2,3‐dimercaptopropanol (DMP), a compound with a strong affinity for lead (Pb). DMP effectively passivates Pb sites in CsPbBr3 (CPB) NCs, enhancing photoluminescence (PL) by forming stable chelating bonds. DMP‐modified CPB nearly completely suppresses hole transfer to ─COOH‐functionalized ferrocene (FcA) and partially suppresses transfer to ─NMe2‐functionalized ferrocene (FcAm), suggesting an alternative hole extraction pathway for FcAm. This is further supported by enhanced hole transfer in bromine‐excess CPB (CPB‐Br(XS)) synthesized via SOBr2 treatment. The distinct binding interactions and charge transfer dynamics are validated through steady‐state and time‐resolved PL, along with transient absorption spectroscopy. These findings underscore the role of strategic ligand engineering in enhancing perovskite NC‐charge acceptor interactions, enabling better charge extraction, higher solar cell efficiency, and reduced lead toxicity through strong Pb binding.