RESUMEN
Perovskite quantum dots (PQDs) become a kind of competitive material for fabricating high-performance solar cells due to their solution processability and outstanding optoelectronic properties. However, the current synthesis method of PQDs is mostly based on the binary-precursor method, which results in a large deviation of the I/Pb input ratio in the reaction system from the stoichiometric ratio of PQDs. Herein, a ternary-precursor method with an iodide source self-filling ability is reported for the synthesis of the CsPbI3 PQDs with high optoelectronic properties. Systematically experimental characterizations and theoretical calculations are conducted to fundamentally understand the effects of the I/Pb input molar ratio on the crystallographic and optoelectronic properties of PQDs. The results reveal that increasing the I/Pb input molar ratio can obtain ideal cubic structure PQDs with iodine-rich surfaces, which can significantly reduce the surface defects of PQDs and realize high orientation of PQD solids, facilitating charge carrier transport in the PQD solids with diminished nonradiative recombination. Consequently, the PQD solar cells exhibit an impressive efficiency of 15.16%, which is largely improved compared with that of 12.83% for the control solar cell. This work provides a feasible strategy for synthesizing high-quality PQDs for high-performance optoelectronic devices.
RESUMEN
CsPbI3 perovskite quantum dot (PQD) shows high potential for next-generation photovoltaics due to their tunable surface chemistry, good solution-processability and unique photophysical properties. However, the remained long-chain ligand attached to the PQD surface significantly impedes the charge carrier transport within the PQD solids, thereby predominantly influencing the charge extraction of PQD solar cells (PQDSCs). Herein, a ligand-induced energy level modulation is reported for band engineering of PQD solids to improve the charge extraction of PQDSCs. Detailed theoretical calculations and systemic experimental studies are performed to comprehensively understand the photophysical properties of the PQD solids dominated by the surface ligands of PQDs. The results reveal that 4-nitrobenzenethiol and 4-methoxybenzenethiol molecules with different dipole moments can firmly anchor to the PQD surface through the thiol group to modulate the energy levels of PQDs, and a gradient band structure within the PQD solid is subsequently realized. Consequently, the band-engineered PQDSC delivers an efficiency of up to 16.44%, which is one of the highest efficiencies of CsPbI3 PQDSCs. This work provides a feasible avenue for the band engineering of PQD solids by tuning the surface chemistry of PQDs for high-performing solar cells or other optoelectronic devices.