Alkali acetate-assisted enhanced electronic coupling in CsPbI3 perovskite quantum dot solids for improved photovoltaics

Fully inorganic CsPbI3 perovskite quantum dots (CsPbI3-PQDs) are known as the best-performing photovoltaic absorber in colloidal quantum dot solar cells. This is achieved by improving the cubic-phase-stabilization and electronic-coupling in CsPbI3-PQD solids. In conventional approaches, the hydrolysis of methyl acetate (MeOAc) resulting in acetic acid and methanol as intermediate substances plays a key role in replacing long-chain hydrocarbons with short-chain ligands, which improves charge transport in the CsPbI3-PQD solids. However, CsPbI3-PQDs suffer from lattice distortion and instability under acidic conditions including protons and polar media, leading to CsPbI3-PQD fusion and poor photovoltaic performance. Herein, we report that electronic coupling and photovoltaic performance of CsPbI3-PQD solids are improved by efficient removal of long-chain oleate ligands using a solution of sodium acetate (NaOAc) in MeOAc, which results in the direct generation of OAc ions without forming protons and methanol. NaOAc-based ligand exchange of CsPbI3-PQDs enables preservation of their nanocrystal size without fusion and minimization of surface trap states originating from metal hydroxide formation on their surfaces. Consequently, the best solar cell comprising NaOAc-treated CsPbI3-PQDs shows an improved device performance with a power conversion efficiency (PCE) of 13.3%, as compared with a lead nitrate-treated control device (12.4% PCE). We demonstrate that sodium acetate (NaOAc) directly generates short-chain OAc ions to exchange the long-chain oleate ligands of CsPbI3 perovskite quantum dots (CsPbI3-PQDs). NaOAc-based ligand exchange enables preservation of CsPbI3-PQD size, minimization of surface trap states, and enhancement of electronic coupling in the resultant CsPbI3-PQD solids. Consequently, NaOAc-treated CsPbI3-PQD solar cells show improved device performance with 12.4% power conversion efficiency. [Display omitted] •NaOAc directly generates short-chain OAc ions to exchange the oleate ligands of CsPbI3-PQDs.•Our strategy enables minimizing the formation of protons and methanol during the ligand exchange.•NaOAc-based ligand exchange enables preserving nanocrystal size and minimizing surface traps.•Resultant CsPbI3-PQD solids show enhanced electronic coupling with improved charge transport.•NaOAc-treated CsPbI3-PQD solar cells show improved photovoltaic performance up to 13.33% PCE.