A major efficiency limit for solution-processed perovskite optoelectronic devices, for example light-emitting diodes, is trap-mediated non-radiative losses. Defect passivation using organic molecules ...has been identified as an attractive approach to tackle this issue. However, implementation of this approach has been hindered by a lack of deep understanding of how the molecular structures influence the effectiveness of passivation. We show that the so far largely ignored hydrogen bonds play a critical role in affecting the passivation. By weakening the hydrogen bonding between the passivating functional moieties and the organic cation featuring in the perovskite, we significantly enhance the interaction with defect sites and minimize non-radiative recombination losses. Consequently, we achieve exceptionally high-performance near-infrared perovskite light-emitting diodes with a record external quantum efficiency of 21.6%. In addition, our passivated perovskite light-emitting diodes maintain a high external quantum efficiency of 20.1% and a wall-plug efficiency of 11.0% at a high current density of 200 mA cm−2, making them more attractive than the most efficient organic and quantum-dot light-emitting diodes at high excitations.Improved understanding of passivation leads to near-infrared perovskite light-emitting diodes with 21.6% external quantum efficiency.
A universal method to obtain record‐high electronic Seebeck coefficients is demonstrated while preserving reasonable conductivities in doped blends of organic semiconductors through rational design ...of the density of states (DOSs). A polymer semiconductor with a shallow highest occupied molecular orbital (HOMO) level‐poly(3‐hexylthiophene) (P3HT) is mixed with materials with a deeper HOMO (PTB7, TQ1) to form binary blends of the type P3HTx:B1‐x (0 ≤ x ≤ 1) that is p‐type doped by F4TCNQ. For B = PTB7, a Seebeck coefficient S = 1100 µV K−1 with conductivity σ = 0.3 S m−1 at x = 0.10 is achieved, while for B = TQ1, S = 2000 µV K−1 and σ = 0.03 S m−1 at x = 0.05 is found. Kinetic Monte Carlo simulations with parameters based on experiments show good agreement with the experimental results, confirming the intended mechanism. The simulations are used to derive a design rule for parameter tuning. These results can become relevant for low‐power, low‐cost applications like (providing power to) autonomous sensors, in which a high Seebeck coefficient translates directly to a proportionally reduced number of legs in the thermogenerator, and hence in reduced fabrication cost and complexity.
Record‐high Seebeck coefficients are achieved for p‐type‐doped blends of common conjugated polymers. The method used is based on a rational design of the density of states, such that the characteristic hop occurs from the compound with the shallower HOMO to the compound with the deeper HOMO.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Doping of organic semiconductors is crucial for the operation of organic (opto)electronic and electrochemical devices. Typically, this is achieved by adding heterogeneous dopant molecules to the ...polymer bulk, often resulting in poor stability and performance due to dopant sublimation or aggregation. In small-molecule donor-acceptor systems, charge transfer can yield high and stable electrical conductivities, an approach not yet explored in all-conjugated polymer systems. Here, we report ground-state electron transfer in all-polymer donor-acceptor heterojunctions. Combining low-ionization-energy polymers with high-electron-affinity counterparts yields conducting interfaces with resistivity values five to six orders of magnitude lower than the separate single-layer polymers. The large decrease in resistivity originates from two parallel quasi-two-dimensional electron and hole distributions reaching a concentration of ∼10
cm
. Furthermore, we transfer the concept to three-dimensional bulk heterojunctions, displaying exceptional thermal stability due to the absence of molecular dopants. Our findings hold promise for electro-active composites of potential use in, for example, thermoelectrics and wearable electronics.
In this Review, we summarize recent work on modeling of organic/metal and organic/organic interfaces. Some of the models discussed have a semiempirical approach, that is, experimentally derived ...values are used in combination with theory, and others rely completely of calculations. The models are categorized according to the types of interfaces they apply to, and the strength of the interaction at the interface has been used as the main factor. We explain the basics of the models, their use, and give examples on how the models correlate with experimental results. We stress that given the complexity of organic/metal and organic/organic interface formation, it is crucial to know the exact way in which the interface was formed before choosing the model that is applicable, as none of the models presented covers the whole range of interface interaction strengths (weak physisorption to strong chemisorption).
Recent developments on modeling of organic/metal and organic/organic interfaces are summarized in this Review. The models are categorized according to the types of interfaces they apply to, and the strength of the interaction at the interface is used as the main factor. We explain the basics of the models, their use, and give examples on how they correlate with experiments.
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Conducting polymers, such as the p-doped poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), have enabled the development of an array of opto- and bio-electronics devices. However, ...to make these technologies truly pervasive, stable and easily processable, n-doped conducting polymers are also needed. Despite major efforts, no n-type equivalents to the benchmark PEDOT:PSS exist to date. Here, we report on the development of poly(benzimidazobenzophenanthroline):poly(ethyleneimine) (BBL:PEI) as an ethanol-based n-type conductive ink. BBL:PEI thin films yield an n-type electrical conductivity reaching 8 S cm
, along with excellent thermal, ambient, and solvent stability. This printable n-type mixed ion-electron conductor has several technological implications for realizing high-performance organic electronic devices, as demonstrated for organic thermoelectric generators with record high power output and n-type organic electrochemical transistors with a unique depletion mode of operation. BBL:PEI inks hold promise for the development of next-generation bioelectronics and wearable devices, in particular targeting novel functionality, efficiency, and power performance.
Nonfullerene (NF) organic solar cells (OSCs) have been attracting significant attention in the past several years. It is still challenging to achieve high‐performance flexible NF OSCs. NF acceptors ...are chemically reactive and tend to react with the low‐temperature‐processed low‐work‐function (low‐WF) interfacial layers, such as polyethylenimine ethoxylated (PEIE), which leads to the “S” shape in the current‐density characteristics of the cells. In this work, the chemical interaction between the NF active layer and the polymer interfacial layer of PEIE is deactivated by increasing its protonation. The PEIE processed from aqueous solution shows more protonated N+ than that processed from isopropyl alcohol solution, observed from X‐ray photoelectron spectroscopy. NF solar cells (active layer: PCE‐10:IEICO‐4F) with the protonated PEIE interfacial layer show an efficiency of 13.2%, which is higher than the reference cells with a ZnO interlayer (12.6%). More importantly, the protonated PEIE interfacial layer processed from aqueous solution does not require a further thermal annealing treatment (only processing at room temperature). The room‐temperature processing and effective WF reduction enable the demonstration of high‐performance (12.5%) flexible NF OSCs.
Protonation of polyethylenimine ethoxylated (PEIE) can effectively passivate the chemical reaction between the PEIE and a nonfullerene (NF) active layer. As a result, the PEIE can work very efficiently as a low‐work‐function interface for NF solar cells. These flexible solar cells exhibit power conversion efficiency up to 12.5% with a room‐temperature‐processed PEIE interface.
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The conjugated polymer poly(3,4-ethylenedioxythiophene) polymerized and stabilized in the presence of polystyrenesulfonate (best known as PEDOT:PSS) is a working horse of organic electronics and ...bioelectronics and one of the most important conductive polymers. While its morphology is complex and depends on the details in synthesis and post-treatment, its distinctive and common feature is a two-phase granular structure attributed to PEDOT- and PSS-rich regions. Yet, there is still no well-established consensus concerning the precise nature of PEDOT- and PSS-rich regions as well as their chemical composition and structure. In this study we perform coarse-grained MARTINI molecular dynamics simulations of PEDOT:PSS focusing on understanding its two-phase morphology as well as water intake and ion exchange. We demonstrate that PEDOT:PSS is an essentially three-component system consisting of positively charged PEDOT chains, PSS chains with mostly deprotonated sulfonate groups, and protonated PSS chains. PEDOT-rich regions are predominantly composed of PEDOT and deprotonated PSS chains, whereas PSS-rich regions are composed of protonated PSS chains. Our calculations unravel how PEDOT- and PSS-rich regions are formed from the solution phase during the drying process. We show that when the dry polymer film is immersed in water, its swells by nearly 60%, and we demonstrate that the origin of swelling is related to deprotonation of the sulfonate groups in the PSS-rich regions. It is mostly PSS-rich regions that swell while the PEDOT-rich regions remain rather unchanged. We demonstrate that swelling of the film is rather insignificant during reduction/oxidation within the cyclic voltammetry (CV) conditions. We show that during CV experiments each counterion brings on overage ≈4 water molecules into the polymer region. Our simulations of swelling, CV experiments, and π–π stacking formation in PEDOT and PSS match well the experimental results. Our theoretical studies unravel the most important morphological aspects of one of the most important polymers for organic electronics, providing the essential insight needed for the material and device design and improvements.
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Being able to dynamically shape light at the nanoscale is one of the ultimate goals in nano-optics
. Resonant light-matter interaction can be achieved using conventional plasmonics based on metal ...nanostructures, but their tunability is highly limited due to a fixed permittivity
. Materials with switchable states and methods for dynamic control of light-matter interaction at the nanoscale are therefore desired. Here we show that nanodisks of a conductive polymer can support localized surface plasmon resonances in the near-infrared and function as dynamic nano-optical antennas, with their resonance behaviour tunable by chemical redox reactions. These plasmons originate from the mobile polaronic charge carriers of a poly(3,4-ethylenedioxythiophene:sulfate) (PEDOT:Sulf) polymer network. We demonstrate complete and reversible switching of the optical response of the nanoantennas by chemical tuning of their redox state, which modulates the material permittivity between plasmonic and dielectric regimes via non-volatile changes in the mobile charge carrier density. Further research may study different conductive polymers and nanostructures and explore their use in various applications, such as dynamic meta-optics and reflective displays.
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FZAB, GEOZS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Although perovskite light-emitting diodes (PeLEDs) have recently experienced significant progress, there are only scattered reports of PeLEDs with both high efficiency and long operational stability, ...calling for additional strategies to address this challenge. Here, we develop perovskite-molecule composite thin films for efficient and stable PeLEDs. The perovskite-molecule composite thin films consist of in-situ formed high-quality perovskite nanocrystals embedded in the electron-transport molecular matrix, which controls nucleation process of perovskites, leading to PeLEDs with a peak external quantum efficiency of 17.3% and half-lifetime of approximately 100 h. In addition, we find that the device degradation mechanism at high driving voltages is different from that at low driving voltages. This work provides an effective strategy and deep understanding for achieving efficient and stable PeLEDs from both material and device perspectives.
Thermoelectric generators (TEGs) transform a heat flow into electricity. Thermoelectric materials are being investigated for electricity production from waste heat (co-generation) and natural heat ...sources. For temperatures below 200 °C, the best commercially available inorganic semiconductors are bismuth telluride (Bi(2)Te(3))-based alloys, which possess a figure of merit ZT close to one. Most of the recently discovered thermoelectric materials with ZT>2 exhibit one common property, namely their low lattice thermal conductivities. Nevertheless, a high ZT value is not enough to create a viable technology platform for energy harvesting. To generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs. This requires thermoelectric materials that are readily synthesized, air stable, environmentally friendly and solution processable to create patterns on large areas. Here we show that conducting polymers might be capable of meeting these demands. The accurate control of the oxidation level in poly(3,4-ethylenedioxythiophene) (PEDOT) combined with its low intrinsic thermal conductivity (λ=0.37 W m(-1) K(-1)) yields a ZT=0.25 at room temperature that approaches the values required for efficient devices.
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