High‐Efficiency Photovoltaic Devices using Trap‐Controlled Quantum‐Dot Ink prepared via Phase‐Transfer Exchange

Abstract

Colloidal-quantum-dot (CQD) photovoltaic devices are promising candidates for low-cost power sources owing to their low-temperature solution processability and bandgap tunability. A power conversion efficiency (PCE) of >10% is achieved for these devices; however, there are several remaining obstacles to their commercialization, including their high energy loss due to surface trap states and the complexity of the multiple-step CQD-layer-deposition process. Herein, high-efficiency photovoltaic devices prepared with CQD-ink using a phase-transfer-exchange (PTE) method are reported. Using CQD-ink, the fabrication of active layers by single-step coating and the suppression of surface trap states are achieved simultaneously. The CQD-ink photovoltaic devices achieve much higher PCEs (10.15% with a certified PCE of 9.61%) than the control devices (7.85%) owing to improved charge drift and diffusion. Notably, the CQD-ink devices show much lower energy loss than other reported high-efficiency CQD devices. This result reveals that the PTE method is an effective strategy for controlling trap states in CQDs.

Decreased Synthesis Costs and Waste Product Toxicity for Lead Sulfide Quantum Dot Ink Photovoltaics

“…The tunable QD bandgaps, [1][2][3][4][5][6] high film stability in air, [2,3,5,6] and solution processability [2][3][4][5][6] could allow for the fabrication of low-cost, large-area devices. The tunable QD bandgaps, [1][2][3][4][5][6] high film stability in air, [2,3,5,6] and solution processability [2][3][4][5][6] could allow for the fabrication of low-cost, large-area devices.…”

“…[5] It has been shown that a significant improvement in QD PV performance can be achieved if the deposited PbS QD films are chemically treated to undergo ligand exchange, replacing OA with shorter ligands, such as halides and short-chain thiols, which leads to high charge conductivities within QD films, boosting the power conversion efficiency of QD PVs. [1][2][3][4] This ink can then be deposited on a substrate to form the QD PV device active layer, [1][2][3][4] with recently reported PbS QD PVs achieving 12% power conversion efficiency (PCE). In a separate synthetic step, OAcapped PbS QDs are exchanged with short ligands in solution and then suspended at a high concentration in a solvent to form an ink.…”

“…[1][2][3][4] This ink can then be deposited on a substrate to form the QD PV device active layer, [1][2][3][4] with recently reported PbS QD PVs achieving 12% power conversion efficiency (PCE). [9][10][11] For example, the leading PbS QD ligand exchange procedures employing lead halides such as lead(II) bromide [1][2][3] and lead(II) iodide [1][2][3][4] have yet to be evaluated with regards to U.S. Environmental Protection Agency and European Union regulatory limits.In this study, we present a solution-phase ligand exchange method that reduces the amount of utilized lead by employing tetrabutylammonium iodide (TBAI) as the source of iodide ligands. A recent report by Jean et al revealed that current solutionphase QD ligand exchange methods create an added cost of $6.30 g −1 of QDs, an expense that negatively impacts the commercial viability of QD PV modules.…”

“…A recent report by Jean et al revealed that current solutionphase QD ligand exchange methods create an added cost of $6.30 g −1 of QDs, an expense that negatively impacts the commercial viability of QD PV modules. The tunable QD bandgaps, [1][2][3][4][5][6] high film stability in air, [2,3,5,6] and solution processability [2][3][4][5][6] could allow for the fabrication of low-cost, large-area devices. [9][10][11] For example, the leading PbS QD ligand exchange procedures employing lead halides such as lead(II) bromide [1][2][3] and lead(II) iodide [1][2][3][4] have yet to be evaluated with regards to U.S. Environmental Protection Agency and European Union regulatory limits.…”

“…Figure 1a shows a schematic diagram of the layers comprising the QD PVs from TBAI ink, including a thin layer of PbS QDs capped with 1,2-ethanedithiol (EDT) that is often required to suppress interfacial recombination. [1][2][3][4] Key differences in device performance between the TBAI ink device and the current certified champion PbS QD ink solar cell fabricated with PbX 2 based ligand exchange methods likely arise from less efficient QD surface passivation following ligand exchange with the TBAI method. This value is approaching the highest-performing PbS QD ink solar cells fabricated to date.…”