Short-Chain Ligand-Passivated Stable α-CsPbI3 Quantum Dot for All-Inorganic Perovskite Solar Cells

Cubic phase CsPbI3 (alpha-CsPbI3) perovskite quantum dots (QDs) have received extensive attention due to their all-inorganic composition and suitable band gap (1.73 eV). However, alpha-CsPbI3 QDs might convert to delta-CsPbI3 (orthorhombic phase with indirect band gap of 2.82 eV) due to easy loss of surface ligands. In addition, commonly used long-chain ligands (oleic acid, OA, and oleylamine, OLA) hinder efficient charge transport in optoelectronic devices. In order to relieve these drawbacks, OA, OLA, octanoic acid, and octylamine are used as capping ligands for synthesizing high-quality alpha-CsPbI3 QDs. The results indicate that these QDs exhibit excellent optical properties and long-term stability compared to QDs capped only with OA and OLA. Moreover, QDs with shorter ligands exhibit an enhanced charge transport rate, which improves the power conversion efficiency of photovoltaic devices from 7.76% to 11.87%.