Computational Screening of Ligands for Enhanced Interactions between Lead Halide Perovskite Quantum Dots.

Ligand choice in nanoparticle systems is vital for developing efficient materials and enhancing electronic and chemical properties. Focusing on CsPbBr, we demonstrate a strategy for modifying the electronic properties of lead halide perovskites through a systematic computational study on ligands with varying binding motifs, sizes, bridge lengths, π-electron conjugation, and electron withdrawing and donating groups. The calculations are benchmarked against experimental data. Choosing a ligand's π-electron system and binding group, followed by tuning the ligand's properties with substituents to the π-system, allows one to introduce ligand electronic states into the perovskite system's bands, close to band edges, and inside the material's fundamental band gap. One can also design surface states by inducing local distortions at the binding site, which can be tuned by altering the binding group of the ligand. Extension of a material's frontier orbitals onto ligands and the creation of surface states make charges available for transport and chemical reactivity, while avoiding charge trapping. In contrast, midgap ligand states trap charges permanently. Large ligands with high coverages interact among themselves, influencing ligand electronic properties and binding. Carboxylate tends to bind more strongly than the ammonium group. Electronegative oxygens in the carboxylate binding group and electron withdrawing substituents bound to the π-system lower ligand orbital energies relative to perovskite states. The reported theoretical analysis guides experimental design of perovskite-ligand systems for optoelectronic, energy, and quantum information applications.