Supramolecular block copolymerzation with optically or electronically complementary monomers provides an attractive bottomup approach for the non-covalent synthesis of nascent axial organic heterostructures, which promises to deliver useful applications in energy conversion, optoelectronics, and catalysis. However, the synthesis of supramolecular block copolymers (BCPs) constitutes a significant challenge due to the exchange dynamics of non-covalently bound monomers and hence requires fine microstructure control. Furthermore, temporal stability of the segmented microstructure is a prerequisite to explore the applications of functional supramolecular BCPs. Herein, we report the cooperative supramolecular block copolymerization of fluorescent monomers in solution under thermodynamic control for the synthesis of axial organic heterostructures with light-harvesting properties. The fluorescent nature of the core-substituted naphthalene diimide (cNDI) monomers enables a detailed spectroscopic probing during the supramolecular block copolymerization process to unravel a nucleation−growth mechanism, similar to that of chain copolymerization for covalent block copolymers. Structured illumination microscopy (SIM) imaging of BCP chains characterizes the segmented microstructure and also allows size distribution analysis to reveal the narrow polydispersity (polydispersity index (PDI) ≈ 1.1) for the individual block segments. Spectrally resolved fluorescence microscopy on single block copolymerized organic heterostructures shows energy migration and light-harvesting across the interfaces of linearly connected segments. Molecular dynamics and metadynamics simulations provide useful mechanistic insights into the free energy of interaction between the monomers as well as into monomer exchange mechanisms and dynamics, which have a crucial impact on determining the copolymer microstructure. Our comprehensive spectroscopic, microscopic, and computational analyses provide an unambiguous structural, dynamic, and functional characterization of the supramolecular BCPs. The strategy presented here is expected to pave the way for the synthesis of multi-component organic heterostructures for various functions.

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Despite having long excited carrier lifetimes and high mobilities in hybrid halide perovskite materials, conventional (n-i-p) devices exhibit significant interfacial nonradiative recombination losses that are little understood but limit the radiative efficiency and the overall open-circuit potential. In this Letter, we reveal that the process of spiro-OMeTAD coating on perovskite gives rise to buried defect states, which are detrimental to the devices’ operational stability. We subsequently report a method to passivate these deleterious buried defect states by atomic layer deposition of Al2O3 through controlled precursor dosages on fully functional devices. The process results in notable improvements in the overall device performance, but the underlying root-cause analysis is what we essentially aimed to elucidate here. The reported passivation technique results in (a) an increase in the efficiency primarily due to an increase of V OC by ∼60–70 mV and consequently (b) enhanced photoluminescence and higher electroluminescence quantum efficiency and (c) overall device operational (MPPT) stability under ambient and, exclusively, even under high vacuum (>300 h) conditions, which is otherwise challenging.

Quasi one-dimensional (1D) semiconductor materials with inherent anisotropic emission have numerous advantages in terms of brightness, color enhancement, and efficiency for optoelectronics and light-emitting devices. Herein, we report the anisotropic optical absorption and emission of individual methyl-ammonium lead bromide (MAPbBr 3 ) microrods (MRs). We find that the absorption and emission polarization direction is along the long axis of the MRs, and the degree of polarization (DOP) remains unaltered with the excitation field orientation as well as with the modulation in excitation energy. Polarization-resolved emission spectroscopy of individual MRs reveals that the orthogonally polarized fluorescence emissions originate from equivalent energy states, in contrast to other semiconductors rods. To explore the polarized PL emission behavior of the diffused photo-excited charge carriers, we employed an optical setup where MRs are locally excited at a confocal spot, and emission is imaged over the entire rod. Although photo-excited carriers in perovskites are known to have short initial polarization memory, we observe anisotropic emission far away, beyond several hundred nanometers from the excitation spot. This is remarkable and indicates strongly polarized radiative recombination of photogenerated carriers which migrate along the long axis of the crystals. Our measurements on single MRs in different dielectric media reveal that the electric field renormalization inside the crystal owing to dielectric changes at the interface is primarily responsible for such observed anisotropy in optical behaviors. The employed imaging method can potentially be used to explore the anisotropic emission behavior of photoexcited and diffused photo-carriers in various other semiconductor microcrystals with different material compositions, where excitation energy is transferred over long distances.

High-throughput fabrication of metal oxide thin films is always a bottleneck for solution-processed perovskite solar cells. Here, we report a rapid photonic curing process, with a well-controlled train of short light pulses, to develop bilayer (colloidal and blocking layer) SnO 2 thin films used as electron transport layers in perovskite ((FA 0.83 MA 0.17 ) 0.95 Cs 0.05 PbI 2.5 Br 0.5 , 1.62 eV band gap) photovoltaic devices (n−i−p architecture) with an optimized efficiency of 21.1% alongside good ambient and operational (MPPT) stability. The strong dependency of the photonic curing pulse parameters on device properties is investigated, and we established a corroboration between the chemical properties of the as-cured SnO 2 and the optoelectronic performance of the devices and the interface quality. Furthermore, we show that the futile removal of the chloride species in photonically cured SnO 2 is an added advantage against the thermally annealed ones regarding charge transport and lower interfacial recombination. Furthermore, the process is impeccably scaled up to demonstrate a series-connected minimodule (16 cm 2 ) with 18.2% efficiency.