Halide perovskites possess enormous potential for various optoelectronic applications. Presently, a clear understanding of the interplay between the lattice and electronic effects is still elusive. Specifically, the weakly absorbing tail states and dual emission from perovskites are not satisfactorily described by existing theories based on the Urbach tail and reabsorption effect. Herein, through temperature-dependent and time-resolved spectroscopy on metal halide perovskite single crystals with organic or inorganic A-site cations, we confirm the existence of indirect tail states below the direct transition edge to arise from a dynamical Rashba splitting effect, caused by the PbBr6 octahedral thermal polar distortions at elevated temperatures. This dynamic effect is distinct from the static Rashba splitting effect, caused by non-spherical A-site cations or surface induced lattice distortions. Our findings shed fresh perspectives on the electronic-lattice relations paramount for the design and optimization of emergent perovskites, revealing broad implications for light harvesting/photo-detection and light emission/lasing applications.

Mixed Ruddlesden-Popper (RP) perovskites are of great interest in light-emitting diodes (LEDs), due to the efficient energy transfer (funneling) from high-bandgap (donor) domains to low-bandgap (acceptor) domains, which leads to enhanced photoluminescence (PL) intensity, long PL lifetime, and high-efficiency LEDs. However, the influence of reduced effective emitter centers in the active emissive film, as well as the implications of electrical injection into the larger bandgap donor material, have not been addressed in the context of an active device. The electrical and optical signatures of the energy cascading mechanisms are critically assessed and modulated in a model RP perovskite series ((C H NH ) (CH(NH ) ) Pb Br ). Optimized devices demonstrate a current efficiency of 22.9 cd A and 5% external quantum efficiency, more than five times higher than systems where funneling is absent. The signature of nonideal funneling in RP perovskites is revealed by the appearance of donor electroluminescence from the device, followed by a reduction in the LED performance.

The incorporation of phenylethylammonium bromide (PEABr) into a fully inorganic CsPbBr perovskite framework led to the formation of mixed-dimensional perovskites, which enhanced the photoluminescence due to efficient energy funnelling and morphological improvements. With a PEABr : CsPbBr ratio of 0.8 : 1, PeLEDs with a current efficiency of 6.16 cd A and an EQE value of 1.97% have been achieved.

3D organic-inorganic lead halide perovskites have shown great potential in efficient photovoltaic devices. However, the low stability of the 3D perovskite layer and random arrangement of the perovskite crystals hinder its commercialization road. Herein, a highly oriented 2D@3D ((AVA) 2 PbI 4 @ MAPbI 3 ) perovskite structure combining the advantages of both 2D and 3D perovskite is fabricated through an in situ route. The highest power conversion efficiency (PCE) of 18.0% is observed from a 2D@3D perovskite solar cell (PSC), and it also shows significantly enhanced device stability under both inert (90% of initial PCE for 32 d) and ambient conditions (72% of initial PCE for 20 d) without encapsulation. The high efficiency of 18.0% and nearly twofold improvement of device stability in ambient compared with pure 3D PSCs confirm that such 2D@3D perovskite structure is an effective strategy for high performance and increasing stability and thus will enable the timely commercialization of PSCs.

With the current research impetus on neuromorphic computing hardware, realizing efficient drift and diffusive memristors are considered critical milestones for the implementation of readout layers, selectors, and frameworks in deep learning and reservoir computing networks. Current demonstrations are predominantly limited to oxide insulators with a soft breakdown behavior. While organic ionotronic electrochemical materials offer an attractive alternative, their implementations thus far have been limited to features exploiting ionic drift a.k.a. drift memristor technology. Development of diffusive memristors with organic electrochemical materials is still at an early stage, and modulation of their switching dynamics remains unexplored. Here, halide perovskite (HP) memristive barristors (diodes with variable Schottky barriers) portraying tunable diffusive dynamics and ionic drift are proposed and experimentally demonstrated. An ion permissive poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate interface that promotes diffusive kinetics and an ion source nickel oxide (NiOx) interface that supports drift kinetics are identified to design diffusive and drift memristors, respectively, with methylammonuim lead bromide (CH3NH3PbBr3) as the switching matrix. In line with the recent interest on developing artificial afferent nerves as information channels bridging sensors and artificial neural networks, these HP memristive barristors are fashioned as nociceptive and synaptic emulators for neuromorphic sensory signal computing.

We utilized two organic dications containing, respectively, a pyridinium and an imidazolium core to construct new n = 1 (where n refers to the number of contiguous 2D inorganic layers; i.e., not separated by organic cations) twodimensional (2D) lead-iodide perovskites 1 and 2. The former material exhibits a (100)-and the latter a very rare 3  3 (110)structural type. Compared with primary ammonium functionality, their constituent ring-centred positive charges have lower charge density. As a result, [PbI6]4-inter-octahedral distortions of the inorganic lattice are reduced (Pb-I-Pb bond angles are as high as 166o and 174o, respectively). This results in bathochromically shifted optical features. In addition, the compact nature of the dications produce super short lead-iodide sheet separations, with respective iodide-iodide (I•••I) distances as small as 4.149 Å and 4.278 Å. These are amongst the shortest separations of adjacent lead-iodide layers, in such materials, ever reported. When crystallized as thin films on top of substrates, the resulting 2D perovskite layers do not adopt a regular growth direction parallel to the surface. Instead, the crystallites grow with no fixed orientation. As a consequence of their proximate inorganic distances and unusual crystallization tendencies, the resulting 2D perovskites exhibit low excitonic activation energies (93.59 meV and 96.53 meV, respectively), enhanced photoconductivity in solar cells, and unprecendented incident photon-to-current conversion rates of up to 60%. More importantly, mesoporous 2D layered perovskite solar cells with power conversion efficiencies (PCEs) of 1.43% and 1.83% were achieved for 1 and 2, respectively. These are the highest values obtained, thus far, for pure n = 1 lead-iodide perovskites and more than 20 times higher than those obtained for materials templated by more conventional cations, such as phenylethylammonium (0.08%).

Despite rapid development of perovskite light emitting diodes (PeLEDs) in recent years, blue PeLEDs' efficiencies are still inferior to their red and green counterparts. The poor performance is associated with, amongst other factors, halide-segregation in bromide-chloride materials and energy funneling to lowest bandgaps in multi-layered Ruddlesden Popper (RP) systems. This study reports that compositional engineering through prudent selection of A-site cation in a pure bromide RP system, a narrow distribution of layered domains can be achieved. With a narrow distribution centred around the desired RP domain, efficient energy cascade to yield blue emission is ensured.Coupled with rapid nucleation induced by antisolvent deposition technique, record efficiencies of 2.34 and 5.08%, corresponding to colour-stable deep blue (~ 465 nm) and cyan (~ 493 nm) respectively, were attained. This composition and process engineering to design favorable structural landscape is transferrable to other material systems which paves the way for high performance PeLEDs.

The synthesis of all-inorganic cesium lead halide perovskite quantum dots (QDs) typically requires high temperatures, stringent conditions, large quantities of surface ligands, and judicious purification steps to overcome ligand-induced charge injection barriers in optoelectronic devices. Low-temperature syntheses generally require lower ligand concentrations, but are severely limited by the low solubility of the Cs precursor. We describe an innovative and general approach under ambient conditions to overcome these solubility limitations, by employing crown ethers. The crown ethers facilitate complete dissolution of the CsBr precursor, rendering CsPbBr3 QD inks practical for device fabrication. The resultant LEDs displayed bright green emission, with a current efficiency, and external quantum efficiency of 9.22 cd A -1 and 2.64%, respectively. This represents the first LED based on CsPbBr3 QDs prepared at room temperature. Lastly, the crown ethers form core-shell structures, opening new avenues to exploit their strong coordination strength.