Periodic Reporting for period 1 - DEOM (Design and Engineering of Optoelectronic Metamaterials)
Reporting period: 2022-10-01 to 2025-03-31
One of the promises of the combination of quantum mechanics and nanotechnology is the ability to design materials with tailor-made physical properties. While there have been several successful examples, as in the case of metamaterials for photonic applications, where colour and refractive index can be tuned by a smart design of the material structure, the development of similar metamaterials for other applications has been lagging.
The project aim to engineer metamaterials for optoelectronic in the visible and near infrared spectral range using as building blocks superlattices quantum wells (QWs) based on layered metal halide perovskites and Pb chalcogenides quantum dots (QDs), respectively. The metamaterials will be assembled from a solution phase using modified Langmuir-Blodgett-Schaefer techniques (both for the QWs and QDs). Ligands will be used in both QDs and QWs superlattices to control the charge carrier transport of the metamaterials providing their full tuneability of properties that will allow to revolutionize the optoelectronic field. The final certification of the quality of the DEOM’s metamaterials will be obtained with the fabrication of near- and short-wavelength infrared photodetectors and visible-light emitting diodes of superior performance levels.
The project aim to engineer metamaterials for optoelectronic in the visible and near infrared spectral range using as building blocks superlattices quantum wells (QWs) based on layered metal halide perovskites and Pb chalcogenides quantum dots (QDs), respectively. The metamaterials will be assembled from a solution phase using modified Langmuir-Blodgett-Schaefer techniques (both for the QWs and QDs). Ligands will be used in both QDs and QWs superlattices to control the charge carrier transport of the metamaterials providing their full tuneability of properties that will allow to revolutionize the optoelectronic field. The final certification of the quality of the DEOM’s metamaterials will be obtained with the fabrication of near- and short-wavelength infrared photodetectors and visible-light emitting diodes of superior performance levels.
As first DEOM aimed to fabricate layer-confined and large size low-dimensional metal halide perovskite quantum well (QW) to use as building blocks for vertically stacked visible optoelectronic metamaterials. We design a liquid surface assembly method similar to Langmuir film formation, where organic-inorganic hybrid perovskite solutions are spread on a liquid substrate and there the crystallization is confined at the liquid-air interface. Through engineering precursor and solvent chemistry, we have achieved large scale growth of over 50 μm lateral sized perovskite sheets, with thickness under 10 nm (5 layers) and high purity in phase composition and optical bandgap.
A low surface energy spreading of the solution was achieved by using acetonitrile as a solvent and phenyl-perfluorinated organic spacer molecules (pentafluorophenylethylammonium, 5FPEA+) in constructing n=1 low dimensional perovskites. The subphase should have a large density as well as surface energy such that the spread solutions can cover the exposed air-liquid interface. In the meantime, its compatibility with the solvents and solutes in perovskite solution needs to be considered to ensure proper crystallization of the 2D perovskite. After several trials, o-xylene and chlorobenzene were found to be the best subphase candidates. All the n=1 sheets obtained have a strong PL emission peak at 510 nm.
Furthermore it was developed an approach to fabricating 2D superlattices of PbS QD in a Langmuir-Schaefer setup with external compression which showed unprecedented area coverage and homogeneity. We have shown that the degree of compression before triggering the ligand exchange is a crucial parameter for obtaining highly ordered, crack-free superlattices. Careful structural characterisation revealed that due to the compression, the ligand-exchanged samples retained the hexagonal geometry thus maximizing the packing of the structure and the number of nearest-neighbours. The control of the lateral compression, and of the structural properties of the superlattices, give rise to significant differences in their transport properties. Ion gel-gated field effect transistors displayed average electron mobility of 5±2 cm2V-1s-1 for the lower compression, increasing to 19±8 cm2V-1s-1 for the highly compressed ones thanks to the better coverage, lack of cracks, better packing and increased translational ordering. This demonstrates the effectiveness of our method in achieving high carrier mobility in superlattices with millimetre square coverage which is unprecedented in literature. Translating this approach to three-dimensional SL as well might have important implications for the technological applications of such metamaterials in optoelectronics.
Another important activity in DEOM has been the fabrication of QDs photodetectors, the activity is very important to prepare not only the right devices structure in view of the use of 3D QD superlattices but also to screen ligands for proper QDs passivation. For the first time, we demonstrated that the MAPbI3 ligand can achieve complete phase-transfer ligand exchange for large-size QDs with excitonic peaks from 1300 nm to 1700 nm. The resulting inks have a prolonged shelf time of at least 10 weeks thanks to the comprehensive passivation of [100] facet. Transport measurements in field-effect transistors showed that our strategy improves carrier mobility and extends the stability for all the QD sizes. The high quality of the inks was further proven by the fabrication by blade coating of high-performance SWIR PbS QDs photodiodes. The resulting device achieved a 76% of EQE at the exciton peak at 1300 nm and 1.8 × 1012 Jones of specific detectivity. This performances are commensurate with the state-of-the-art literature reports of short wavelenght infrared (SWIR) QDs photodetectors fabricated by spin-coating deposition. This is an extremely important demonstration as it reveals the scalable (and not wasteful) fabrication of SWIR PbS QDs photodetectors without performance loss.
A low surface energy spreading of the solution was achieved by using acetonitrile as a solvent and phenyl-perfluorinated organic spacer molecules (pentafluorophenylethylammonium, 5FPEA+) in constructing n=1 low dimensional perovskites. The subphase should have a large density as well as surface energy such that the spread solutions can cover the exposed air-liquid interface. In the meantime, its compatibility with the solvents and solutes in perovskite solution needs to be considered to ensure proper crystallization of the 2D perovskite. After several trials, o-xylene and chlorobenzene were found to be the best subphase candidates. All the n=1 sheets obtained have a strong PL emission peak at 510 nm.
Furthermore it was developed an approach to fabricating 2D superlattices of PbS QD in a Langmuir-Schaefer setup with external compression which showed unprecedented area coverage and homogeneity. We have shown that the degree of compression before triggering the ligand exchange is a crucial parameter for obtaining highly ordered, crack-free superlattices. Careful structural characterisation revealed that due to the compression, the ligand-exchanged samples retained the hexagonal geometry thus maximizing the packing of the structure and the number of nearest-neighbours. The control of the lateral compression, and of the structural properties of the superlattices, give rise to significant differences in their transport properties. Ion gel-gated field effect transistors displayed average electron mobility of 5±2 cm2V-1s-1 for the lower compression, increasing to 19±8 cm2V-1s-1 for the highly compressed ones thanks to the better coverage, lack of cracks, better packing and increased translational ordering. This demonstrates the effectiveness of our method in achieving high carrier mobility in superlattices with millimetre square coverage which is unprecedented in literature. Translating this approach to three-dimensional SL as well might have important implications for the technological applications of such metamaterials in optoelectronics.
Another important activity in DEOM has been the fabrication of QDs photodetectors, the activity is very important to prepare not only the right devices structure in view of the use of 3D QD superlattices but also to screen ligands for proper QDs passivation. For the first time, we demonstrated that the MAPbI3 ligand can achieve complete phase-transfer ligand exchange for large-size QDs with excitonic peaks from 1300 nm to 1700 nm. The resulting inks have a prolonged shelf time of at least 10 weeks thanks to the comprehensive passivation of [100] facet. Transport measurements in field-effect transistors showed that our strategy improves carrier mobility and extends the stability for all the QD sizes. The high quality of the inks was further proven by the fabrication by blade coating of high-performance SWIR PbS QDs photodiodes. The resulting device achieved a 76% of EQE at the exciton peak at 1300 nm and 1.8 × 1012 Jones of specific detectivity. This performances are commensurate with the state-of-the-art literature reports of short wavelenght infrared (SWIR) QDs photodetectors fabricated by spin-coating deposition. This is an extremely important demonstration as it reveals the scalable (and not wasteful) fabrication of SWIR PbS QDs photodetectors without performance loss.
In the first two years of the project DEOM several results that go beyond the state of the art have been achieved.
We have demonstrated the liquid surface growth of halide perovskite sheets; our work represents a first proof of concept towards synthesizing layer controlled QWs in an efficient and large-scale manufacturing process. This opens to the fabrication of heterostructures with advanced optoelectronic functionality.
We have shown the fabrication of 2D superlattices (SL) of PbS colloidal quantum dots over large areas by utilizing the Langmuir-Schaefer technique. By means of the barrier’s compression, the film is densified, and the crack formation is significantly suppressed. At higher compression we achieved smooth homogeneous films that are crack-free over several square millimetres in size. The transport properties of the 2D SL were tested in a field-effect transistor with ion-gel gating, devices fabricated with the high compression films reached mobility up to 36.6 cm2V-1s-1. This is an extremely important result as, if it could be demonstrated also for multilayers, it opens to the use of superlattices for the fabrication of highly performing short wavelength infrared photodetectors.
We demonstrate that methylammonium lead iodide ligands can provide sufficient passivation of PbS QDs of size up to 6.7 nm, enabling inks with a minimum of ten-week shelf-life time, as proven by optical absorption and solution-small angle X-ray scattering. Furthermore, the maximum linear electron mobility of 4.5 × 10-2 cm2 V-1 s-1 was measured in field-effect transistors fabricated with fresh inks, while transistors fabricated with the same solution after ten-week storage retained 74% of the average starting electron mobility, demonstrating the outstanding quality both of the fresh and aged inks. Finally, photodetectors fabricated via blade-coating exhibited 76% external quantum efficiency at 1300 nm and 1.8 × 1012 Jones specific detectivity, values comparable with devices fabricated using ink with lower stability and wasteful methods such as spin-coating.
We have demonstrated the liquid surface growth of halide perovskite sheets; our work represents a first proof of concept towards synthesizing layer controlled QWs in an efficient and large-scale manufacturing process. This opens to the fabrication of heterostructures with advanced optoelectronic functionality.
We have shown the fabrication of 2D superlattices (SL) of PbS colloidal quantum dots over large areas by utilizing the Langmuir-Schaefer technique. By means of the barrier’s compression, the film is densified, and the crack formation is significantly suppressed. At higher compression we achieved smooth homogeneous films that are crack-free over several square millimetres in size. The transport properties of the 2D SL were tested in a field-effect transistor with ion-gel gating, devices fabricated with the high compression films reached mobility up to 36.6 cm2V-1s-1. This is an extremely important result as, if it could be demonstrated also for multilayers, it opens to the use of superlattices for the fabrication of highly performing short wavelength infrared photodetectors.
We demonstrate that methylammonium lead iodide ligands can provide sufficient passivation of PbS QDs of size up to 6.7 nm, enabling inks with a minimum of ten-week shelf-life time, as proven by optical absorption and solution-small angle X-ray scattering. Furthermore, the maximum linear electron mobility of 4.5 × 10-2 cm2 V-1 s-1 was measured in field-effect transistors fabricated with fresh inks, while transistors fabricated with the same solution after ten-week storage retained 74% of the average starting electron mobility, demonstrating the outstanding quality both of the fresh and aged inks. Finally, photodetectors fabricated via blade-coating exhibited 76% external quantum efficiency at 1300 nm and 1.8 × 1012 Jones specific detectivity, values comparable with devices fabricated using ink with lower stability and wasteful methods such as spin-coating.