Modulating Singlet and Triplet Energy Transfer Pathways in Halide Perovskite-Cyanine Dye Hybrids Through Mn-Doping

Tailoring the energy and charge transfer in semiconductor nanocrystal-dye assemblies is vital for developing light harvesting and light-emitting systems with greater efficiency. Metal halide perovskites can capture photons over a wide range of visible and near-infrared wavelengths and are capable of sensitizing singlet and triplet states of dye molecules. The energy transfer pathways can be controlled by a careful selection of donor-acceptor energy levels, spectral overlap, and functionalization of acceptor dyes. However, the singlet and triplet characteristics of nanocrystals for dictating energy transfer remain unexplored. Herein, we have successfully introduced Mn²⁺ doping in CsPb(Br_0.3Cl_0.7)₃ nanocrystals to enhance the triplet properties, thereby directing the energy transfer to cyanine dyes. Independently probing the energy transfer from excitonic and Mn²⁺ states indicates both singlet and triplet energy transfer to surface-bound cyanine dyes are operative. Additionally, varying the Mn²⁺ concentration in Mn-doped CsPb(Br_0.3Cl_0.7)₃ nanocrystals allowed us to resolve the contribution of Mn²⁺ states in singlet/ triplet energy transfer pathways. The emission and transient absorption analysis presented here provides new insights for increasing the triplet properties of semiconductor nanocrystals for designing nanocrystal-dye assemblies for light harvesting systems.