Metal halide perovskite semiconductors possess outstanding characteristics for optoelectronic applications including but not limited to photovoltaics. Low-dimensional and nanostructured motifs impart ...added functionality which can be exploited further. Moreover, wider cation composition tunability and tunable surface ligand properties of colloidal quantum dot (QD) perovskites now enable unprecedented device architectures which differ from thin-film perovskites fabricated from solvated molecular precursors. Here, using layer-by-layer deposition of perovskite QDs, we demonstrate solar cells with abrupt compositional changes throughout the perovskite film. We utilize this ability to abruptly control composition to create an internal heterojunction that facilitates charge separation at the internal interface leading to improved photocarrier harvesting. We show how the photovoltaic performance depends upon the heterojunction position, as well as the composition of each component, and we describe an architecture that greatly improves the performance of perovskite QD photovoltaics.
We present a cation-exchange approach for tunable A-site alloys of cesium (Cs+) and formamidinium (FA+) lead triiodide perovskite nanocrystals that enables the formation of compositions spanning the ...complete range of Cs1–x FA x PbI3, unlike thin-film alloys or the direct synthesis of alloyed perovskite nanocrystals. These materials show bright and finely tunable emission in the red and near-infrared range between 650 and 800 nm. The activation energy for the miscibility between Cs+ and FA+ is measured (∼0.65 eV) and is shown to be higher than reported for X-site exchange in lead halide perovskites. We use these alloyed colloidal perovskite quantum dots to fabricate photovoltaic devices. In addition to the expanded compositional range for Cs1–x FA x PbI3 materials, the quantum dot solar cells exhibit high open-circuit voltage (V OC) with a lower loss than the thin-film perovskite devices of similar compositions.
Colloidally grown nanosized semiconductors yield extremely high‐quality optoelectronic materials. Many examples have pointed to near perfect photoluminescence quantum yields, allowing for ...technology‐leading materials such as high purity color centers in display technology. Furthermore, because of high chemical yield, and improved understanding of the surfaces, these materials, particularly colloidal quantum dots (QDs) can also be ideal candidates for other optoelectronic applications. Given the urgent necessity toward carbon neutrality, electricity from solar photovoltaics will play a large role in the power generation sector. QDs are developed and shown dramatic improvements over the past 15 years as photoactive materials in photovoltaics with various innovative deposition properties which can lead to exceptionally low‐cost and high‐performance devices. Once the key issues related to charge transport in optically thick arrays are addressed, QD‐based photovoltaic technology can become a better candidate for practical application. In this article, the authors show how the possibilities of different deposition techniques can bring QD‐based solar cells to the industrial level and discuss the challenges for perovskite QD solar cells in particular, to achieve large‐area fabrication for further advancing technology to solve pivotal energy and environmental issues.
The possibilities of different deposition techniques which can bring quantum dot (QD)‐based solar cells to the industrial level are assessed. With perovskite QDs showing dramatic improvements in photovoltaics, the discussions on the challenges particularly for perovskite QD solar cells are given in an attempt to achieve large‐area fabrication solving pivotal energy and environmental issues.
A detailed picture of temperature dependent behavior of Cs
FA
PbI
perovskite quantum dots across the composition range is constructed by performing in situ optical spectroscopic and structural ...measurements, supported by theoretical calculations that focus on the relation between A-site chemical composition and surface ligand binding. The thermal degradation mechanism depends not only on the exact chemical composition, but also on the ligand binding energy. The thermal degradation of Cs-rich perovskite quantum dots is induced by a phase transition from black γ-phase to yellow δ-phase, while FA-rich perovskite quantum dots with higher ligand binding energy directly decompose into PbI
. Quantum dot growth to form large bulk size grain is observed for all Cs
FA
PbI
perovskite quantum dots at elevated temperatures. In addition, FA-rich quantum dots possess stronger electron-longitudinal optical phonon coupling, suggesting that photogenerated excitons in FA-rich quantum dots have higher probability to be dissociated by phonon scattering compared to Cs-rich quantum dots.
Colloidal all-inorganic CsPbI3 perovskite quantum dots (PQDs) have shown tremendous potential in photovoltaic applications in recent years due to their outstanding optoelectronic properties that ...general metal halide perovskites offer, along with the added advantages that originates from size reduction and the quantum confinement effect. However, the issue of low carrier mobility in PQD films caused by insulating organic ligands capped on the PQD surface still remains to be addressed while aiming for high-efficiency PQD solar cells. Herein, we propose a novel strategy that takes benefits of ionic liquids, which can offer the high polarity and the electron donating ability to boost the mobility of PQD films in photovoltaic devices. Specifically, 1-propyl-3-methylimidazolium iodide to modulate the colloidal CsPbI3 PQD surface and couple QDs is demonstrated for the first time. The lone pair electrons on the nitrogen of the imidazole ring within the ionic liquid binds to the empty nonbonding surface orbitals of CsPbI3 PQDs while the long-chain insulating ligands are replaced, which enables not only efficient charge transport but also reduced defect density in the assembled PQD solid films. The resulting CsPbI3 PQD solar cell shows a significant increase in efficiency with suppressed hysteresis, indicating the impressive potential of this strategy for developing highly efficient PQD solar cells.
Colloidal metal halide perovskite nanocrystals (NCs) with chiral ligands are outstanding candidates as a circularly polarized luminescence (CPL) light source due to many advantages such as high ...photoluminescence quantum efficiency, large spin–orbit coupling, and extensive tunability via composition and choice of organic ligands. However, achieving pronounced and controllable polarized light emission remains challenging. Here, we develop strategies to achieve high CPL responses from colloidal formamidinium lead bromide (FAPbBr3) NCs at room temperature using chiral surface ligands. First, we show that replacing a portion of typical ligands (oleylamine) with short chiral ligands ((R)-2-octylamine) during FAPbBr3 NC synthesis results in small and monodisperse NCs that yield high CPL with average luminescence dissymmetry g-factor, g lum = 6.8 × 10–2. To the best of our knowledge, this is the highest among reported perovskite materials at room temperature to date and represents around 10-fold improvement over the previously reported colloidal CsPbCl x Br y I3‑x‑y NCs. In order to incorporate NCs into any optoelectronic or spintronic application, the NCs necessitate purification, which removes a substantial amount of the chiral ligands and extinguishes the CPL signals. To circumvent this issue, we also developed a postsynthetic ligand treatment using a different chiral ligand, (R-/S-)methylbenzylammonium bromide, which also induces a CPL with an average g lum = ±1.18 × 10–2. This postsynthetic method is also amenable for long-range charge transport since methylbenzylammonium is quite compact in relation to other surface ligands. Our demonstrations of high CPL and g lum from both as-synthesized and purified perovskite NCs at room temperature suggest a route to demonstrate colloidal NC-based spintronics.
CsPbI3 nanocrystals with narrow size distributions were prepared to study the size-dependent properties. The nanocrystals adopt the perovskite (over the nonperovskite orthorhombic) structure with ...improved stability over thin-film materials. Among the perovskite phases (cubic α, tetragonal β, and orthorhombic γ), the samples are characterized by the γ phase, rather than α, but may have a size-dependent average tilting between adjacent octahedra. Size-dependent lattice constants systematically vary 3% across the size range, with unit cell volume increasing linearly with the inverse of size to 2.1% for the smallest size. We estimate the surface energy to be from −3.0 to −5.1 eV nm–2 for ligated CsPbI3 nanocrystals. Moreover, the size-dependent bandgap is best described using a nonparabolic intermediate confinement model. We experimentally determine the bulk bandgap, effective mass, and exciton binding energy, concluding with variations from the bulk α-phase values. This provides a robust route to understanding γ-phase properties of CsPbI3.
Colloidal halide perovskite nanocrystals (NCs) have the possibility of easy scale-up due to their batch synthesis and have demonstrated excellent optoelectronic properties. In particular, perovskite ...NCs have remarkably high photoluminescence quantum yields in solution and as thin films and impressive open circuit voltages in photovoltaic devices. Despite these promising results, little work has been done to understand the stability of CsPbI3 NCs for optoelectronic device applications. It has been previously shown that the ligands impart tensile surface strain, which stabilizes the black three-dimensional (3D) perovskite phase against phase degradation, making CsPbI3 NCs some of the most structurally robust inorganic halide perovskites to date. However, understanding exactly how CsPbI3 NCs degrade under ambient conditions is critical. We demonstrate that the degradation mechanism of NCs is unique from, and 2 orders of magnitude slower than, their polycrystalline thin-film counterparts. Under specific conditions, CsPbI3 NC films show a compositional instability instead of the phase instability seen in large grain CsPbI3. This is mediated through reactions with superoxide and other reactive oxygen species, which are initiated from surface defect states, O2 and light. We then use this mechanistic insight to identify multiple strategies to prolong the lifetimes of CsPbI3 NC films, by going beyond surface strain to mitigate key surface chemistries. We demonstrate that (1) minimizing the number of surface defects (2) using an alkylammonium bromide ligand surface treatment and (3) encapsulation with an oxygen scavenging layer all increase NC film lifetimes by inhibiting various steps in the photo-oxidation degradation reaction.
As lead halide perovskite (LHP) semiconductors have shown tremendous promise in many application fields, and particularly made strong impact in the solar photovoltaic area, low dimensional quantum ...dot forms of these perovskites are showing the potential to make distinct marks in the fields of electronics, optoelectronics and photonics. The so-called perovskite quantum dots (PQDs) not only possess the most important features of LHP materials, i.e., the unusual high defect tolerance, but also demonstrate clear quantum size effects, along with exhibiting desirable optoelectronic properties such as near perfect photoluminescent quantum yield, multiple exciton generation and slow hot-carrier cooling. Here, we review the advantageous properties of these nanoscale perovskites and survey the prospects for diverse applications which include light-emitting devices, solar cells, photocatalysts, lasers, detectors and memristors, emphasizing the distinct superiorities as well as the challenges.
This review summarizes the advantageous properties of lead halide perovskite quantum dots and surveys the prospects for diverse applications which include light-emitting devices, solar cells, photocatalysts, lasers, detectors and memristors, emphasizing the distinct superiorities as well as the challenges. Display omitted
•Emerging halide perovskite quantum dots (HPQDs) are timly and informatively reviewed.•HPQDs advantageous properties and application potential are insightfully discussed.•Challenges of energy-efficient sustainable applications based on HPQDs are proposed.•This review article can serve as a source of information on future of HPQDs.
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