Combining Perovskites and Quantum Dots: Synthesis, Characterization, and Applications in Solar Cells, LEDs, and Photodetectors

Metal halide perovskites having high defect tolerance, high absorption characteristics, and high carrier mobility demonstrate great promise as potential light harvesters in photovoltaics and optoelectronics and have experienced an unprecedented development since their occurrence in 2009. Semiconductor quantum dots (QDs), on the other hand, have also been proved to be very flexible toward shape, dimension, bandgap, and optical properties for constructing optoelectronic devices. Of late, a strategic combination of both materials has demonstrated extraordinary promise in photovoltaic applications and optoelectronic devices. Combining QDs and perovskites has proved to be quite an effective strategy toward the formation of pinhole-free and more stable perovskite crystals along with tunability of other properties. To boost this exciting research field, it is imperative to summarize the work done so far in recent years to provide an intriguing insight. This review is a critical account of the advanced strategy toward combining these two fascinating materials, including their different synthetic approaches regarding heteroepitaxial growth of perovskite crystals on QDs, carrier dynamics at the interface and potential application in the field of solar cells, light emitting diodes, and photodetectors.S.R. acknowledges Marie Skłodowska-Curie Actions (Project H2020-MSCA-IF-2019-897030). This work was supported by MCIN/AEI/ 10.13039/501100011033, JCCM (FEDER) and the European Union (EU) through projects PID2020-116519RB-I00 and SBPLY/19/180501/000212, respectively; and by the European Research Council (ERC) via Consolidator Grant (724424-No-LIMIT). P.P. acknowledges the support from National Science Centre (Poland) through project No. 2017/26/D/ST3/00910

Perovskite-Quantum Dots Interface: Deciphering its Ultrafast Charge Carrier Dynamics

Understanding electron and hole (e,h) transport at semiconductor interfaces is paramount to developing efficientoptoelectronic devices. Halide perovskite/semiconductor quantum dots (QDs) have emerged as smart hybridsystems with a huge potential for light emission and energy conversion. However, the dynamics of generated e-hpairs are not fully understood. Ultrafast UV–VIS transient absorption and THz spectroscopies have enabled us tounravel the processes of the e-h recombination within a hybrid film of methylammonium lead triiodide (MAPbI3)interacting with different amount of PbS/CdS core/shell QDs. To accurately analyze the complex behavior, weapplied a new model for e-h events in this hybrid material. The results obtained with sample having a highconcentration of QDs (7.3 mass percentage) indicate: (i) a large population (92%) of the photogenerated chargecarriers are affected by QDs presence. The main part of these carriers (85% of the total) in perovskite domaindiffuse towards QDs, where they transfer to the interface (electrons) and QD´s valence bands (holes) with rateconstants of 1.2 × 1010s−1and 4.6 × 1010s−1, respectively. 7% of these affected charged entities are excitonsin the perovskite domain in close vicinity of the interface, and show a recombination rate constant of 3.7 × 1010s−1.(ii) The carriers not affected by QDs presence (8%) recombine through known perovskite deactivationchannels. Lowering the QDs mass percentage to 0.24 causes a decrease of electron and hole effective transfer rateconstants, and disappearance of excitons. These results provide clues to improve the performance of perovskite/QD based device

Deciphering the Role of Quantum Dots Size in the Ultrafast Charge Carrier Dynamics at the Perovskite-Quantum Dots Interface

Understanding the behaviour of electrons and holes (e, h) diffusion and transfer at the interfaces of photoexcited hybrid materials at different densities of photoexcited charge carriers is paramount to the development of efficient optoelectronic devices. Nanocomposites formed by methylammonium lead iodide perovskite (MAPbI3) and semiconductor colloidal quantum dots (QDs)are among these hybrid materials under intensive studies. However, the reciprocal influence of the components in the composite material on the temporal evolution of the photoinduced charge carriers is still poorly explored. This study explores the ultrafast temporal behaviour of the photoexcited charge carriers in MAPbI3/PbS QDs films, letting a special attention to the role of the PbS QD size. Armed with fs-time-resolved UV-VIS transient absorption and terahertz techniques, we unravel the effect of different sizes of PbS QDs, embedded in perovskite (PS) host matrix, on the processes of e and h diffusion, transfer to the QDs phase and recombination. While the decays are dominated by e and h transition from PS to QDs, the increase in the size of QDs results in an acceleration of the charge carriers transition processes represented by the total transition rate constants of electrons (ke) and holes (kh). The total ke and kh values change form 0.1and 1 (109 s-1) to 4.5and 22 (109 s-1), respectively. We extract the rate constants of their diffusions (kediff = 2.2 × 1010s-1 and khdiff = 1.1 × 1010 s-1) and transfers to the interfaces (ket = 0.1 to 1.6 × 1010 s-1 and kht = 0.1 to 0.8 × 1010 s-1). Furthermore, the analysis of spectral behavior of PS and PS/QDs upon pumping with different fs-laser fluences indicate the presence and photoformation of excitonic states. The acceleration of such processes decreases the contribution of undesirable charge carriers trapping and non-radiative recombination within PS

Absorption Enhancement in Peridinin–Chlorophyll–Protein Light-Harvesting Complexes Coupled to Semicontinuous Silver Film

We report on experimental and theoretical studies of plasmon-induced effects in a hybrid nanostructure composed of light-harvesting complexes and metallic nanoparticles in the form of semicontinuous silver film. The results of continuous-wave and time-resolved spectroscopy indicate that absorption of the light-harvesting complexes is strongly enhanced upon coupling with the metallic film spaced by 25 nm of a dielectric silica layer. This conclusion is corroborated by modeling, which confirms the morphology of the silver island film

Fuel Cells in Road Vehicles

Issues related to the reduction of the environmental impact of means of road transport by the use of electric motors powered by Proton Exchange Membrane (PEM) fuel cells are presented in this article. The overall functional characteristics of electric vehicles are presented, as well as the essence of the operation of a fuel cell. On the basis of analyzing the energy conversion process, significant advantages of electric drive are demonstrated, especially in vehicles for urban and suburban applications. Moreover, the analyzed literature indicated problems of controlling and maintaining fuel cell power caused by its highest dynamic and possible efficiency. This control was related to the variable load conditions of the fuel cell vehicle (FCV) engine. The relationship with the conventional dependencies in the field of vehicle dynamics is demonstrated. The final part of the study is related to the historical outline and examples of already operating fuel cell systems using hydrogen as an energy source for energy conversion to power propulsion vehicle’s engines. In conclusion, the necessity to conduct research in the field of methods for controlling the power of fuel cells that enable their effective adaptation to the temporary load resulting from the conditions of vehicle motion is indicated

Enhancing Anticorrosion Resistance of Aluminum Alloys Using Femtosecond Laser-Based Surface Structuring and Coating

We report a robust two-step method for developing adherent and anticorrosive molybdenum (Mo)-based coatings over an aluminum (Al) 6061 alloy substrate using a femtosecond (fs) laser. The fs laser nanostructuring of Al 6061 alloy in air gives rise to regular arrays of microgrooves exhibiting superhydrophilic surface properties. The microstructured surface is further coated with an Mo layer using the fs-pulsed laser deposition (fs-PLD) technique. The combination of the two femtosecond laser surface treatments (microstructuring followed by coating) enabled the development of a highly corrosion-resistant surface, with a corrosion current of magnitude less than that of the pristine, the only structured, and the annealed alloy samples. The underlying mechanism is attributed to the laser-assisted formation of highly rough hierarchical oxide structures on the Al 6061 surface along with post heat treatment, which passivates the surface and provide the necessary platform for firm adhesion for Mo coating. Our results reveal that the corrosive nature of the Al-based alloys can be controlled and improved using a combined approach of femtosecond laser-based surface structuring and coating

On the Correlation between the Geometrical Features and Thermal Efficiency of Flat-Plate Solar Collectors

This article presents the results of numerical and experimental studies on the impacts of the selected geometrical features of liquid solar collectors on their thermal efficiency. The experiments were carried out while meeting the requirements of the ISO 9806:2017 standard. Selected changes in the geometrical features were analysed by using fully functional prototypes of modified solar collectors. The correlations between the design and performance properties of the solar collectors were determined in accordance with the changes in the shape of the thermal efficiency η(T*m) curve

The Effect of the Mixture Composition of BmimBF4-Acetonitrile on the Excited State Relaxation Dynamics of a Solar Cell Dye D149: An Ultrafast Transient Absorption Study

It has been recognized that the understanding of the photo physic of the dyes used in solar cells in an important step in improving their efficiency. Certainly using ionic liquid as an electrolyte is a good solution as it stabilizes the excited state of the dye, however, because of the high viscosity, the diffusion of the components of the solar cell (dye, electrolyte, the chosen redox couple) is very low and has consequences on the other processes (Forward and backward processes). One of the ideas, is to modulate the viscosity of the ionic liquid by mixing the ionic liquid with a solvent. The goal then of this work is to quantify the mixture composition dependence of the excited state relaxation times. Other studies should be carried out to quantify the mixture dependence on the time characteristics of other processes (charge injection, collection etc.) to optimize the working optimal conditions of the solar cell. Following this goal, the present study is devoted to characterize the relaxation time of in the whole mixture composition of BmimBF4 and acetonitrile and in the neat components. For the first time, the decay relaxation times of the first excited electronic state of D149 dye, as obtained by transient absorption spectroscopy (TAS). These relaxation times are monitored by a gradual change of the local structure around a dye, from the one dominated by the interionic interactions, high viscosity and low polarity (as quantified by the static dielectric constant) in BmimBF4 to the one that is dominated by dipole-dipole interactions, low viscosity and high polarity in acetonitrile.<br /

Perovskite-Quantum Dots Interface: Deciphering its Ultrafast Charge Carrier Dynamics

Understanding electron and hole (e,h) transport at semiconductor interfaces is paramount to developing efficientoptoelectronic devices. Halide perovskite/semiconductor quantum dots (QDs) have emerged as smart hybridsystems with a huge potential for light emission and energy conversion. However, the dynamics of generated e-hpairs are not fully understood. Ultrafast UV–VIS transient absorption and THz spectroscopies have enabled us tounravel the processes of the e-h recombination within a hybrid film of methylammonium lead triiodide (MAPbI3)interacting with different amount of PbS/CdS core/shell QDs. To accurately analyze the complex behavior, weapplied a new model for e-h events in this hybrid material. The results obtained with sample having a highconcentration of QDs (7.3 mass percentage) indicate: (i) a large population (92%) of the photogenerated chargecarriers are affected by QDs presence. The main part of these carriers (85% of the total) in perovskite domaindiffuse towards QDs, where they transfer to the interface (electrons) and QD´s valence bands (holes) with rateconstants of 1.2 × 1010s−1and 4.6 × 1010s−1, respectively. 7% of these affected charged entities are excitonsin the perovskite domain in close vicinity of the interface, and show a recombination rate constant of 3.7 × 1010s−1.(ii) The carriers not affected by QDs presence (8%) recombine through known perovskite deactivationchannels. Lowering the QDs mass percentage to 0.24 causes a decrease of electron and hole effective transfer rateconstants, and disappearance of excitons. These results provide clues to improve the performance of perovskite/QD based device

Unraveling Charge Carriers Generation, Diffusion, and Recombination in Formamidinium Lead Triiodide Perovskite Polycrystalline Thin Film.

We report on studies of the formamidinium lead triiodide (FAPbI3) perovskite film using time-resolved terahertz (THz) spectroscopy (TRTS) and flash photolysis to explore charge carriers generation, migration, and recombination. The TRTS results show that upon femtosecond excitation above the absorption edge, the initial high photoconductivity (∼75 cm(2) V(-1) s(-1)) remains constant at least up to 8 ns, which corresponds to a diffusion length of 25 μm. Pumping below the absorption edge results in a mobility of 40 cm(2) V(-1) s(-1) suggesting lower mobility of charge carriers located at the bottom of the conduction band or shallow sub-bandgap states. Furthermore, analysis of the THz kinetics reveals rising components of <1 and 20 ps, reflecting dissociation of excitons having different binding energies. Flash photolysis experiments indicate that trapped charge carriers persist for milliseconds