Snaith group

Abstract:

Having captivated the research community with simple fabrication processes and staggering device efficiencies, perovskite-based optoelectronics are already on the way to commercialization. However, one potential obstacle to this commercialization is the almost exclusive use of toxic, highly coordinating, high boiling point solvents to make perovskite precursor inks. Herein, we demonstrate that nonpolar organic solvents, such as toluene, can be combined with butylamine to form an effective solvent for alkylammonium-based perovskites. Beyond providing broader solvent choice, our finding opens the possibility of blending perovskite inks with a wide range of previously incompatible materials, such as organic molecules, polymers, nanocrystals, and structure-directing agents. As a demonstration, using this solvent, we blend the perovskite ink with 6,6-phenyl-C-61-butyric acid methyl ester and show improved perovskite crystallization and device efficiencies. This processing route may enable a myriad of new possibilities for tuning the active layers in efficient photovoltaics, light-emitting diodes, and other semiconductor devices.

Abstract:

Oleylamine and oleic acid are common organic capping ligands used in the hot injection preparation of perovskite quantum dots (QDs). Their labile nature is responsible for the poor colloidal stability and conductivity that affect the performance of perovskite QD light-emitting diodes (LEDs). We introduced 4-trifluoro phenethylammonium iodide (CF₃PEAI) directly in the synthesis and found that CF₃PEAI efficiently modified the I^- vacancy defects on the QD surface and partially substituted the surface capping ligand oleylamine. The strong electron pulling ability of F in CF₃PEAI results in a more positive -NH₃⁺ terminal compared to that of PEAI, which promotes tight bonding of CF₃PEAI on the surface of CsPbI₃ QDs. As a result, we achieved bright QDs with a photoluminescence quantum yield of 92% and efficient red LEDs. The maximal luminance was improved to 4550 cd m^-2 for 685 nm red light, which was nearly 4.6-fold of the LEDs with plain CsPbI₃ QDs. Additionally, the peak external quantum efficiency reached 12.5%.