Comparing Halide Ligands in PbS Colloidal Quantum Dots for Field-Effect Transistors and Solar Cells

Abstract

Capping colloidal quantum dots (CQDs) with atomic ligands is a powerful approach to tune their properties and improve the charge carrier transport in CQD solids. Efficient passivation of the CQD surface, which can be achieved with halide ligands, is crucial for application in optoelectronic devices. Heavier halides, i.e., I– and Br–, have been thoroughly studied as capping ligands in the last years, but passivation with fluoride ions has not received sufficient consideration. In this work, effective coating of PbS CQDs with fluoride ligands is demonstrated and compared to the results obtained with other halides. The electron mobility in field-effect transistors of PbS CQDs treated with different halides shows an increase with the size of the atomic ligand (from 3.9 × 10–4 cm2/(V s) for fluoride-treated to 2.1 × 10–2 cm2/(V s) for iodide-treated), whereas the hole mobility remains unchanged in the range between 1 × 10–5 cm2/(V s) and 10–4cm2/(V s). This leads to a relatively more pronounced p-type behavior of the fluoride- and chloride-treated films compared to the iodide-treated ones. Cl–- and F–-capped PbS CQDs solids were then implemented as p-type layer in solar cells; these devices showed similar performance to those prepared with 1,2-ethanedithiol in the same function. The relatively stronger p-type character of the fluoride- and chloride-treated PbS CQD films broadens the utility of such materials in optoelectronic devices.

Orthogonal colloidal quantum dot inks enable efficient multilayer optoelectronic devices

“…The BA-functionalized CQD films showed shorter PL lifetime than did OA-capped CQD films (Fig. 2d ), which may be attributed to exciton dissociation via charge or energy transfer caused by the enhanced inter-dot coupling 31 , 32 . The EDT-exchanged film showed a substantially reduced PL lifetime compared to the BA-functionalized CQD films.…”

Design Strategy of Quantum Dot Thin‐Film Solar Cells

“…[59] Thus, treatment with short ligands such as 3-mercaptopropionic acid (MPA), 1,2-ethanedithiol (EDT), or with atomic halide ligands is essential to fabricating junction-type thin-film QD solar cells. [15,60,61] In 2008, Luther et al reported Schottky solar cells based on EDT-treated PbSe QDs between Indiumdoped tin oxide (ITO) and a metal electrode. [14] Atomic ligand treatment based on an organic ammonium halide salt was later introduced by Tang et al [62] This atomic ligand results in a much shorter interdot distance with improved mobilities compared with short organic ligands.…”

“…[ 59 ] Thus, treatment with short ligands such as 3‐mercaptopropionic acid (MPA), 1,2‐ethanedithiol (EDT), or with atomic halide ligands is essential to fabricating junction‐type thin‐film QD solar cells. [ 15,60,61 ] In 2008, Luther et al. reported Schottky solar cells based on EDT‐treated PbSe QDs between Indium‐doped tin oxide (ITO) and a metal electrode.…”

“…The mobility of QDs was dramatically improved when the interdot distance was shortened through the adoption of short ligands such as organic ligands with a small number of carbons or halide atomic ligands. [15] Moreover, the modification of surface dipoles by doping led to a structural evolution from simple Schottky solar cells to heterojunction solar cells. [12] Recent progress in QD thin-film solar cells has focused on surface modification of QDs because the main deficient device characteristic that remains to overcome is the surface trapping of QDs.…”

Sensitization of SnO2 Single Crystals with Multidentate‐Ligand‐Capped PbS Colloid Quantum Dots to Enhance the Photocurrent Stability

“…In recent years, colloidal quantum dots (QDs) have been widely explored for various applications, including photovoltaics (PV), [1][2][3][4] field-effect transistors, [5,6] light-emitting diodes, [7][8][9] and other solar energy conversion applications. [10][11][12][13][14] Due to their quantum-confinement effect, QDs have size-tunable band gaps that, depending on material and size, can range from the ultraviolet (UV) to near-infrared (NIR).…”