Effect of Surface Ligand on Charge Separation and Recombination at CsPbI₃ Perovskite Quantum Dot/TiO₂ Interfaces

Abstract

CsPbI3 perovskite quantum dot (QD) solar cells are a promising device platform for further development due to their improved stability compared to bulk materials. The fabrication of these devices often involves postsynthetic washing of colloidal QDs to remove surface ligands. Herein, we investigate how this postsynthetic treatment affects the charge separation (CS) and charge recombination (CR) processes at the interface of CsPbI3 QDs and the TiO2 electron extraction layer. The CS time constant at QD/TiO2 interface decrease from 457 ± 4 ps for QDs directly deposited on TiO2 to 288 ± 1 ps for QDs that were washed twice by methyl acetate, increasing the ET efficiency from 89.9 ± 0.3% to 98.3 ± 0.01%. Interestingly, this treatment also lengthens the average charge recombination time constants from 346 ± 18 ns to 1180 ± 60 ns, which is also beneficial for reducing charge recombination loss. This result demonstrates the pronounced effect of QD washing by methyl acetate (MeOAc) on interfacial charge transfer processes, suggesting the important effect of postsynthesis modification of colloidal perovskite QDs on solar cell efficiencies.

Recent Advances in Ligand Design and Engineering in Lead Halide Perovskite Nanocrystals

“…[433] After loss of ligand density following washing procedures, the charge separation rates decreased, which corresponds to an increase in charge separation efficiency. [433] In addition to ligand density, identity of the ligands passivating the LHP NCs used for photovoltaic applications is also very important for device performances. A slow charge recombination process is typically required in order to minimize the competition with separating excited electrons in the conduction band (CB) and holes in the valence band (VB).…”

CsPbBr3–CdS heterostructure: stabilizing perovskite nanocrystals for photocatalysis

“…1,2 The ability to chemically modify the surface with a functionalized ligand or to couple with another semiconductor particle offers a variety of ways to harvest visible photons. [3][4][5] Since the 1990s, metal chalcogenide quantum dots (QDs), CdSe in particular, have served as the prototypical compound to elucidate excited state and charge transfer properties. [6][7][8] In recent years, another quantum dot system, viz., perovskite nanocrystals (CsPbX 3 , X ¼ Cl, Br, I), has emerged as a model semiconductor QD system to probe light induced optoelectronic and photocatalytic properties.…”

Perovskite Quantum Dots in Solar Cells

“…Afterward, Shang et al quantified the effect of post purification on the charge dynamic process at the CsPbI 3 PQDs/TiO 2 electron transport layers (ETLs) interface. [ 68 ] The charge separation time constant in the purified PQDs/TiO 2 films is 288 ± 1 ps, shorter than that (457 ± 4 ps) in original PQDs/TiO 2 . While the charge recombination time constants raised from 346 ± 18 ns to 1180 ± 60 ns upon post purification.…”