Manipulation of Phase-Transfer Ligand-Exchange Dynamics of PbS Quantum Dots for Efficient Infrared Photovoltaics

Abstract

Chemical surface treatment of colloidal quantum dots (CQDs) by phase-transfer ligand-exchange (PTLE) is essential to implement highly densified, well-passivated CQD films for optoelectronic applications, such as infrared photovoltaics, light-emitting diodes, and photodetectors. PTLE, however, involves parallel and interactional processes of ligand exchange, phase transfer, and surface passivation of CQDs, which render the optimization of PTLE still challenging. Herein, we explored the action mechanism of a widely used additive, ammonium acetate (AA), on the PTLE of PbS CQDs to recognize the dynamic balance during the PTLE process and its impact on the performance of colloidal quantum dot solar cells (CQDSCs). Our research definitely shows that the AA additive can modify the dynamics of PTLE by participating in all of the three processes, and the amount of AA significantly influences the defect passivation and colloidal stability of PbS CQDs. At an appropriate concentration (∼50 mM) of AA, PbS CQDs are well iodide-passivated by PTLE, and the fabricated CQDSCs achieve a power conversion efficiency (PCE) of ∼10% associated with improved carrier transport and reduced trap-assisted carrier recombination. However, excessive AA causes trace residual AA on the CQD surface, resulting in the insufficient surface passivation of PbS CQDs and trap issues of CQDSCs. The double-edged sword effect of the AA additive on PTLE, demonstrated in our work, suggests that realizing a dynamic balance of different processes during PTLE is crucial for further performance promotion of CQDSCs.

Annealing-Temperature Dependent Carrier-Transportation in ZnO/PbS Quantum Dot Solar Cells Fabricated Using Liquid-Phase Ligand Exchange Methods

“…Liquid-phase ligand exchange made it possible to achieve more efficient and uniform passivation on the surface of CQDs compared with solid-phase ligand exchange. As a result, the liquid-phase ligand exchange method has gained popularity for achieving high-efficiency CQD-based solar cell performance [31][32][33][34][35][36][37][38]. In addition to CQD solution deposition methods and conditions, the post-treatment of the deposited CQD films is equally important for the construction of QD solid films with better QD coupling and fewer defect states [33,38].…”

“…Next, we focused on the PbS QD film properties, such as the amount of organic residue and defect density, and investigated the influence of these factors on carrier transport characteristics. We first estimated the defect density of the QD films using the following equations [36]:…”

Variation of Surface Nanostructures on (100) PbS Single Crystals during Argon Plasma Treatment

“…The unique properties of these materials are associated with with their large exciton Bohr radii (18-50 nm) and the generation of multiple excitons. In addition, wide variety of synthesis methods capable of controlled formation of nanostructures with various shapes and sizes opens broad prospects for practical application [3][4][5]. PbX nanostructures can be formed by a large number of methods, including hydrothermal method [6], hightemperature synthesis [7], synthesis in aqueous solutions [8], molecular beam epitaxy [9], and synthesis in polymer and glass matrices [10,11].…”

Efficient PbS Quantum Dot Solar Cells with Both Mg-Doped ZnO Window Layer and ZnO Nanocrystal Interface Passivation Layer

“…PbS colloidal quantum dot (CQD) solar cells have been rapidly developed in recent years with a certified power conversion efficiency (PCE) up to 13% in an optimal device configuration [ 1 , 2 ]. Compared to traditional photovoltaic technology, PbS CQD solar cells show great potential applications in energy products in view of their low cost, low temperature, and simple solution processing techniques [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ]. More importantly, the bandgap of PbS CQDs can be easily controlled by varying the size of the CQDs, which enables efficient harvesting of a broad light spectrum from the visible to infrared region.…”