Multifaceted anchoring ligands for uniform orientation and enhanced cubic-phase stability of perovskite quantum dots

All-inorganic CsPbI₃ perovskite quantum dots (PQDs) hold significant potential for next-generation photovoltaics due to their unique optoelectronic properties, and the surface-bound ligand playing a key role in the stability and functionality of CsPbI₃ PQDs. Initially used long-chain ligands in PQDs synthesis stabilize the black phase but hinder charge transport when employed to solar cells, necessitating their replacement with shorter ones. However, this leads to the formation of surface defects and loss of tensile strain, resulting in the transition to the undesired orthorhombic phase (δ-phase) and compromising PQD solar cell performance. Therefore, developing a ligand exchange process that achieves the optimal balance between conductivity and stability in PQD solid films continues to be a significant challenge. To address these issues, we developed an efficient ligand-exchange process utilizing a multifaceted anchoring ligand, 2-thiophenemethylammonium iodide (ThMAI). The larger ionic size of ThMA⁺ compared to Cs⁺ facilitates the restoration of surface tensile strain in PQDs, while its thiophene and ammonium groups enable effective passivation of surface defects. Owing to these advantages, ThMAI-treated CsPbI₃ PQD thin films exhibit improved carrier lifetime, uniform PQD orientation, and increased ambient stability. As a result, the ThMAI-treated CsPbI₃ PQD solar cells demonstrate an improved power conversion efficiency (PCE) of 15.3 % and an enhanced device stability.