SUpramolecularly engineered functional PERovskite quantum wells

Project Information

SUPER

Grant agreement ID: 101040681

DOI

10.3030/101040681

EC signature date 31 January 2022

Start date 1 June 2023

End date 28 February 2029

Funded under

• European Research Council (ERC)

Total cost

€ 2 474 375,00

EU contribution

€ 2 474 375,00

Coordinated by

ALMA MATER STUDIORUM - UNIVERSITA DI BOLOGNA
Italy

Periodic Reporting for period 1 - SUPER (SUpramolecularly engineered functional PERovskite quantum wells)

Reporting period: 2023-06-01 to 2025-11-30

Summary of the context and overall objectives of the project

Metal halide perovskites (MHPs) are promising semiconductors for optoelectronic applications. However, trap-mediated non-radiative losses and low exciton binding energy limit the maximum luminescence efficiency representing a bottleneck for light emitting applications. The metal halide framework is also prone to rapid degradation, while the extensive use of lead adds serious toxicity concerns.
Low-dimensional layered MHPs incorporating bulkier organic cations have emerged as alternative to improve radiative recombination efficiency and grant increased chemical and environmental stability. These consist in two-dimensional (2D) structures made of alternating organic and inorganic sheets behaving like multi-quantumwells. Currently, the majority of works rely on simple insulating cations: they only play a templating role for the structural properties, while the reduced conductivity frustrates their implementation in optoelectronic devices.
The next frontier is the development of organic semiconductors which can take an active role in the energetic landscape of the material while acting as building block for the construction of the perovskite. Sparse efforts have been made for the incorporation of more complex cations. Nevertheless, the range of functional cations successfully implemented in 2D perovskites remains limited.

SUPER will develop low-dimensional MHPs exploiting synergistic effects between the metal halide framework and organic semiconductors, intimately integrated at themo lecular level in ordered extended solids. This requires an increase in structural complexity compared to standard MHPs bringing them into the realm of hybrid supramolecular structures. As such, this project addresses long-standing synthetic challenges encompassing several fields of chemistry, materials science and nanotechnology, related to the unpredictability of how the individual components self-assemble in complex superstructures, which represents a stunning block to the rational development of new architectures with targeted functionalities. This will be achieved by targeting the following objectives:

1) Development of a toolbox of functional organic semiconductors with suitable molecular geometries for integration in the perovskite framework.
2) Control over the perovskite self-assembly and supramolecular structure.
3) Development of functional MHPs quantum wells with widely tunable and efficient luminescence.
4) Improvement of charge transport of 2D perovskites enabling efficient integration in electrically-driven light emitting devices.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The work performed in SUPER involves:

- The design and synthesis of molecular building blocks. The templating cations are engineered in terms of: conjugated core, determining the main photophysical properties through control of the conjugation length extension, aromaticity and planarity; linker(s), including the positively charged tethering unit(s) defining the cation’s binding character; linear or ring-forming substituents, added for their electron withdrawing/donating character to promote n- and p-type conductivity, enhance electron delocalization, force molecular planarization, tune and enhance the luminescence yield, improve solubility and modulate the molecular association and crystal packing.

- The self-assembly of perovskite multi-quantum wells. SUPER targets layered perovskites of the Ruddlesden-Popper (L2An-1BnX3n+1) and Dion-Jacobson (LAn-1BnX3n+1) series, where X is a halide (F-, Cl-, Br-, I-), B is a divalent metal, n indicates the dimensionality connected to the thickness of the inorganic layers, A is a small organic cation (e.g. methylammonium) and L indicates a large mono or di-topic functional cation. SUPER aims to rationalize the effects of chemical composition on the perovskite’s connectivity, defectivity, rigidity and formation of related structural motifs. X-Ray duffraction and solid state NMR are used in combination to retrieve complementary structural informations. In particular, ssNMR is exploited to probe with high resolution the interatomic and intermolecular interactions, the local level of static and dynamic disorder as well as the presence of multiple phases and impurities, without stringent requirements in terms of sample crystallinity.

- The photophysical characterization of the perovskites. SUPER aims at the creation of a functional hybrid platform which can efficiently harness both the radiative excitonic recombination in the perovskite’s inorganic phase and the highly versatile luminescence of organic semiconductors. Optical spectroscopy is used to detrmine the type of internal energy level alignment of the quantum wells defining the photophysical properties of each type of heterojunction. SUPER further investigates how the crystal structure affects the optical properties of the material to establish close structural-properties correlations. The luminescence is investigated for both non-coherent and coherent light-emitting applications.

- The realization of electrically-driven light-emitting devices based on low-dimensional perovskites. The reduced transport properties coupled with the strong charge confinement in the inorganic wells of currently available low-dimensional perovskites represent a major unsolved challenge which blocks their effective exploitation and dramatically reduces their technological relevance. SUPER combines complementary strategies to greatly enhance the conductivity of MHP quantum wells and study their impact on charge transport at a fundamental level. Light-emitting field-effect transistors (LE-FETs) and light-emitting diodes (LEDs) are fabricated to study both the electrical transport and the electroluminescent properties of these low-dimensional semiconductors.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

SUPER will generate a new fundamental understanding of how large molecular and atomic systems interact to form hybrid superstructures with targeted and technologically relevant functionalities. This will establish an unprecedented level of control for the rational synthesis of complex MHP quantum wells, with radically enhanced charge transport and luminescence, and photophysical properties going beyond those accessible with currently available MHPs. At the same time, it will provide solutions to the main stability and toxicity issues which afflict the entire field of MHPs. The extensive application of ssNMR on low-dimentional MHPs planned in this project, in conjunction with X-ray diffraction techniques, will also open a completely new perspective on the structural properties of these materials. Overall, this will pave the way to the efficient exploitation of low-dimensional perovskites as both coherent and incoherent light sources with potentially disruptive impact in advanced multiband photonic platforms and lab-on-a-chip systems.
SUPER will also have a wide multidisciplinary impact beyond MHPs and photonics. The elucidation of structure-function relationships will create innovative crystal engineering strategies for the control of light-matter interaction and improvement of electronic coupling and delocalization in complex architectures through synthetic design. This will be of great relevance for a large class of emerging supramolecular energy materials for photovoltaic, photocatalysis, solar-to-fuel energy conversion and energy storage.