2D matrix engineering for homogeneous quantum dot coupling in photovoltaic solids

Abstract

Colloidal quantum dots (CQDs) are promising photovoltaic (PV) materials because of their widely tunable absorption spectrum controlled by nanocrystal size. Their bandgap tunability allows not only the optimization of single-junction cells, but also the fabrication of multijunction cells that complement perovskites and silicon . Advances in surface passivation, combined with advances in device structures , have contributed to certified power conversion efficiencies (PCEs) that rose to 11% in 2016 . Further gains in performance are available if the thickness of the devices can be increased to maximize the light harvesting at a high fill factor (FF). However, at present the active layer thickness is limited to ~300 nm by the concomitant photocarrier diffusion length. To date, CQD devices thicker than this typically exhibit decreases in short-circuit current (J) and open-circuit voltage (V), as seen in previous reports. Here, we report a matrix engineering strategy for CQD solids that significantly enhances the photocarrier diffusion length. We find that a hybrid inorganic-amine coordinating complex enables us to generate a high-quality two-dimensionally (2D) confined inorganic matrix that programmes internanoparticle spacing at the atomic scale. This strategy enables the reduction of structural and energetic disorder in the solid and concurrent improvements in the CQD packing density and uniformity. Consequently, planar devices with a nearly doubled active layer thicknesses (~600 nm) and record values of J (32 mA cm) are fabricated. The V improved as the current was increased. We demonstrate CQD solar cells with a certified record efficiency of 12%.

Spin-coated planar Sb2S3 hybrid solar cells approaching 5% efficiency

“…1) and other absorber materials [7–10 12–13 16–20]. Experimental solar cell performance compared to the Shockley–Queisser SQ limit (a).…”

“…The record efficiency of 7.5% [6] is comparable to that of other less investigated materials, such as the best lead-free perovskites [7], Cu 2 O [8] and Sb 2 Se 3 [9–10] and outperforms bismuth-halides [11–12], SnS [13] and Bi 2 S 3 [14–16]. However, the efficiency of Sb 2 S 3 trails behind the more thoroughly studied material systems such as lead-based perovskites [17], organic solar cells [18–19] or PbS [20], thus further technological investigation is needed. Two basic factors that impact the solar cell performance of a given material are the device architecture, which defines the mechanism of charge separation, and the deposition method for the absorber, which affects the film and electronic material quality.…”

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

“…[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.…”

“…[5] Solution-phase ligand exchange is currently the leading method of preparing the active layers in top-performing PbS QD PVs. [1] With this advancement the fabrication of the active layer is now more facile, however, the scalability of PbS QD solar cells is still uncertain. [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).…”

“…[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.…”