Conjugated hairy-rod polymers, which have emerged as promising photocathode materials for solar-fuel production, are comprised of stiff, low-entropy backbones and complex side-chain substitutions, which collectively affect assembly compared to flexible-chain materials. Here, we unravel the relationship between structural and electronic disorder in a model hairy-rod polymer, PBTTT. We identify a narrow electronic density-of-states (DOS) distribution with weak spatial variations in PBTTT, while the prototypical flexible-chain polymer, P3HT, features an energetically broad, spatially variable DOS. We assign this observation to the fact that PBTTT is structurally homogeneous due to its liquid-crystalline-like behavior, contrary to the structurally heterogeneous, semi-crystalline P3HT. This view is further supported by 2D electronic spectroscopy, which reveals that PBTTT features dynamic electronic disorder, vs. P3HT, which exhibits primarily static electronic disorder. Collectively, our work provides understanding into the disordered energy landscape in conjugated hairy-rod polymers, towards accelerated materials discovery for renewable energy technologies.
Immense efforts in the flexible electronics field have led to unprecedented progress and to devices of ever increasing performance. Despite these advances, new opportunities are sought in order to widen the applications of flexible electronics technologies, expand their functionalities/features, with an increasing view on delivering sustainable solutions. We discuss here opportunities the use of multicomponent systems for, e.g., increasing the mechanical flexibility and stability of organic electronic products, or introducing other features such as self-encapsulation and more robust transport. We demonstrate the working principle of semiconductor:insulator blends, examining the different approaches that have recently been reported in literature. We illustrate how organic solar cells (OPV)s can be fabricated with such systems without detrimental effects on the resulting device characteristics even at high contents of the insulator.
Novel optical materials based on oxide hydrate/poly(vinyl alcohol) hybrids are presented that have a readily tunable refractive index and can be solution-processed into photonic structures, including dielectric mirrors, gratings, and beyond. In planar microcavities, strong light–matter coupling is achieved at the target excitation. The agreement between classical electrodynamic simulations of the microcavity response and the experimental data demonstrates that the entire microcavity stack can be controllably produced as designed. Because of the versatility of the hybrid material used in these microcavities as high refractive index material, structures with a wide spectral range of optical modes might be designed and produced with straightforward coating methodologies, enabling fine-tuning of the energy and lifetime of the microcavities‘ optical modes to harness strong light–matter coupling in a wide variety of solution processable active materials.
In organic and organic/inorganic hybrid materials, the role of the exciton reservoir (i.e., uncoupled excitons) towards populating exciton-polariton states —emerging when an excitonic transition strongly couples with a microcavity optical mode— is not well understood. Here, we identify many-body processes in the exciton reservoir by probing the time-resolved nonlinear photoluminescence of polaritons in an organic dye (1,6,7,12-bay-substituted perylene-diimide derivative) and a Ruddlesden-Popper (PEA)2PbI4 perovskite. We observe that, in the dye, exciton-exciton annihilation is hindered in the strong light-matter coupling regime and, in (PEA)2PbI4, Auger recombination obstructs the population of exciton-polaritons via radiative pumping by the emission of the exciton reservoir.
In recent years, hairy rod semiconducting polymers have risen to the forefront of organic electronic implementations for, among other factors, their desirable photophysical properties. Departing from conventional semiflexible polymers, the newer generation of materials have increased backbone rigidity. This evokes the question of how increasing rigidity manifests in the photophysical response of these materials. Herein, we use solid-state vacuum compression molding to induce elusive liquid crystallinity in quintessential thermotropic Poly[2,5-bis(3-dodecylthiophen-2-yl)thieno[3,2-b]thiophene], PBTTT. By means of conventional and fast calorimetry, we elucidate the changes in phase behavior of solution processed PBTTT upon solid-state compression. Furthermore, anisotropy, associated with liquid crystallinity, is observed through transmission X-ray scattering. The shift towards increased anisotropy strongly influences the photophysical aggregation of transition dipole moments as it determines the local ordering of chromophores. We probe the optical response as a function of temperature to determine dominant aggregation states and further exemplify local ordering. This work provides a framework for controlling photophysical response in thermotropic or liquid crystalline-like polymer semiconductors by means of processing.
Organic electronic materials possess unique opto-electronic and processing properties that provide broad opportunities for use in light-emitting diodes, solar-energy harvesting systems, to next-generation sensors and neuromophic computing components. These technologies have been continually improving over the past decades, aided by advancements in materials chemistry and processing innovation. State-of-the-art polymer semiconductors typically have an electron donor-acceptor (D-A) backbone structure with a number of fused ring moieties, and complex aliphatic or, e.g., ethylene-oxide side chains that decorate the backbone to provide solubility. It is important to recognize that the physical properties of the side chains are substantially different from the backbone, constituting an amphiphilic-like characteristics transverse to the backbone reminiscent of phospholipid and surfactant molecular analogs, and simple classical descriptions of amorphous vs. semicrystalline structure no longer apply. Here, we discuss how the FSC technique can be used for the identification of thermodynamic transitions of next generation D-A polymers commonly used in the organic solar cell area to obtain important structural information of this new class of materials and, in turn, establish processing guidelines towards materials of specific optical or electrical characteristics, and improved materials design for organic optoelectronic devices.
We designed and fabricated highly reflective polymer-based chirped mirrors for thermal management using a titanium oxide hydrate/poly(vinyl alcohol) hybrid as the high-refractive-index material and a commodity polymer as the low-refractive-index material. Typically, chirped reflectors are fabricated using inorganic dielectrics incompatible with large-area and flexible applications. All-organic alternatives suffer from a small refractive index contrast between layers, limiting reflectivity. By employing this inorganic/organic hybrid material with a tunable refractive index (1.5-2.1), we accomplish a large enough refractive index contrast with commodity polymers and contribute towards making these photonic structures more readily accessible for heat management purposes.
In recent years, immense efforts in the flexible electronics field have led to unprecedented progress and to devices of ever increasing performance. Despite these advances, new opportunities are sought in order to widen the applications of organic-based technologies and expand their functionalities and features. We discuss here challenges and opportunities, with focus on the use of multicomponent systems for, e.g., increasing the mechanical flexibility and stability of organic electronic products, or introducing other features such as self-encapsulation and faster mixed ion-electron transport. One specific strategy is based on blending polymeric insulators with organic semiconductors; which has led to a desired improvement of the mechanical properties of organic devices, producing in certain scenarios robust and stable architectures. Here we discuss the working principle of semiconductor:insulator blends, examining the different approaches that have recently been reported in literature. We illustrate how organic field-effect transistors (OFET)s and organic solar cells (OPV)s can be fabricated with such systems without detrimental effects on the resulting device characteristics even at high contents of the insulator. Furthermore, we review how blending can assist in the fabrication of more reliable and versatile organic electrochemical transistors (OECT)s.
The absorption of a photon by Organic Semiconductors (OSCs) results in the formation of a bound electron-hole pair quasiparticle or Frenkel Exciton. The energy required to separate an exciton into noninteracting electron and hole, Exciton Binding Energy (Eb), is a critical parameter for the purpose of improving the efficiency of optoelectronic devices such as solar cells and light emitting diodes. In the last two decade there have been many efforts to measure the Eb of OSCs using different techniques. However, there are discrepancies in the literature and the reported values are scattered over a large range between a few meV to 1.5eV, even for a specific material. Eb of Frenkel excitons can be estimated as the difference between the transport (Eg) and the optical gap (Eopt), a traditional definition borrowed from the language of Wannier Exciton in inorganic SCs. Here, we explore the Eb of different variants of PBnDT-FTAZ polymer. We focus on the two most common methods used to measure Eg: combination of Ultraviolet Photoelectron Spectroscopy and Inversed Photoelectron Spectroscopy (UPS-IPES) and Solid-State Cyclic Voltammetry (CV). We show that Eb measured by the abovementioned methods are not consistent or correlated with each other. The Eg measured by UPS-IPES technique is comparable with (or even smaller than) Eopt leading to small Eb. On the other hand, CV usually measures larger Eg compared to the Eopt resulting in larger values of Eb that are scattered between 200meV-1eV depending on the molecular structure of the materials. This discrepancy is the result of lack of both an exclusive theoretical and a functional definition of Eb that includes the relaxation effects, an important characteristic of Frenkel excitons. Moreover, due to the nature of each measurement method, they might measure different parameters than the actual properties of the bulk in a photovoltaic device. Our results elucidate the current conundrum on determination of Eb in OSCs and emphasize the importance of establishing standard theoretical and practical guidelines on how to properly estimate Eb.
The question of how free charges are generated in donor:acceptor blends requires consideration that they are typically comprised of a complex phase morphology where intermixed and relatively phase-pure domains of the donor and acceptor co-exist. The local arrangement of the donor and acceptor plays thereby a decisive role in the fate of photogenerated electron-hole pairs –whether they dissociate to free charges or geminately recombine– as we demonstrate on a series of donor polymer:fullerenes binaries by combining 2D-NMR, time-resolved ultra-fast spectroscopy and detailed structural data. Our insights are important as similar considerations apply to other blends, such as semiconductor:dopant binaries that lead to highly conductive systems. We discuss how the spatial arrangement affects charge transport, and provide a tentative picture of the complex correlation of structure and electronic landscape towards the understanding of organic photovoltaics and doped, conducting plastics.
We have used a femtosecond-resolved spectroscopic technique based on the Stark effect (electromodulated
differential absorption) in order to investigate free charge generation and charge drift in solar cell devices of
neat conjugated polymer pBTTT and in its 1:1 (by weight) blend with PCBM. In the latter, the fullerene
molecules intercalate between the polymer side-chains, yielding a co-crystal phase. Our results show that free
charge generation in both materials is ultrafast and strongly dependent on the applied reverse bias. Charge
drift to the electrodes (under strong reverse bias) occurs with comparable dynamics on the 1.2 ns time scale
for neat pBTTT and the blend, and is probably dominated by hole transport within/between polymer chains.
In this work, we study the nature of long-lived photoexcitations in intercalated, partially and
predominantly non-intercalated semicrystalline poly(2,5-bis(3-tetradecyl-thiophen-2-yl)thieno
[3,2,-b]thiophene) (pBTTT):phenyl-C61 -butyric acid methyl ester (PC61BM) blend films by
quasi-steady-state photoinduced absorption (PIA) spectroscopy. We find that polarons are generated in
these microstructures. However, the polarons generated in partially and predominantly non-intercalated
films (1.7 eV) are at higher energy than in intercalated film (1.4 eV). After comparing with the polaron
generation in neat pBTTT polymer film, we propose that the polarons generated in partially and
predominantly non-intercalated film are delocalized charges, and the polarons generated in intercalated
film are localized charges. Furthermore, we also find that the polarons generated in the partially
non-intercalated film have the longest lifetime.
Polymeric semiconductors such has regioregular poly(3-hexylthiophene) have electronic proprieties that can be tuned by proper control of the solid-state microstructure. We process thin films of P3HT of different molecular weight ranging from 2 kg/mol to 341 kg/mol. The polymer undergo a transition from a paraffinic, non-entangled microstructure to a two-phase microstructure defined by entangled chains embedded in amorphous regions at around 50 kg/mol. We observe an abrupt decrease in the intermolecular coupling from an average of ~20 meV for molecular weight below 50 kg/mol to ~5 meV above 50 kg/mol. We assign this decrease in the interchain coupling and associated free-exciton bandwidth at higher molecular weight to a transition from a one-phase morphology to a two-phase morphology defined above. In steady-state photoluminescence, we associate the lower Huang-Rhys factors at higher molecular weight to more planar backbone.
The formation of a well-defined, reproducible ZnO nanorod scaffold for hybrid photovoltaic applications has been investigated. A standard hydrothermal growth method was used and the influence of chemical additions in controlling length, width, density, and orientation was studied. The nanostructures prepared have been characterized by scanning electron microscopy, x-ray diffraction, UV-visible spectroscopy in addition to measurement of the wetting behavior. A standard procedure for the production of vertically orientated nanorods with a narrow size distribution, high areal density, and good wettability in aqueous solutions is presented.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.