Tomasz Marszalek

Molecular engineering of face-on oriented dopant-free hole transporting material for perovskite solar cells with 19% PCE

Through judicious molecular engineering, novel dopant-free star-shaped D–π–A type hole transporting materials coded KR355, KR321, and KR353 were systematically designed, synthesized and characterized. KR321 has been revealed to form a particular face-on organization on perovskite films favoring vertical charge carrier transport and for the first time, we show that this particular molecular stacking feature resulted in a power conversion efficiency over 19% in combination with mixed-perovskite (FAPbI3)0.85(MAPbBr3)0.15. The obtained 19% efficiency using a pristine hole transporting layer without any chemical additives or doping is the highest, establishing that the molecular engineering of a planar donor core, π-spacer and periphery acceptor leads to high mobility, and the design provides useful insight into the synthesis of next-generation HTMs for perovskite solar cells and optoelectronic applications.

Combination of Two Diketopyrrolopyrrole Isomers in One Polymer for Ambipolar Transport

were presented. As a regioisomer of DPP1whose polymers can be used as ambipolar transporters in manycases, DPP2-containing polymers should also exhibit ambipo-larity upon appropriate molecular design which, however, is sofar elusive.In view of the key role of well-established DPP1 and thepotential of DPP2 in the design of conjugated polymersemiconductors, it appears highly appropriate to combine thesetwo isomers in one polymer main chain. Herein, we report acopolymer (PDPP1-DPP2, Figure 1) containing two DPPisomers separated by a bithiophene unit in one polymerbackbone. The two “homo”-polymers (PDPP1 and PDPP2)incorporating only one DPP isomer coupled with bithiopheneare also prepared for studying contribution of each isomer tootpoelectronic behavior of PDPP1-DPP2. Optical and electro-chemical studies indicate that PDPP1-DPP2 exhibits anabsorption band and an energy gap located in between thoseof PDPP1 and PDPP2. OFETs based on PDPP1-DPP2 showambipolar charge carrier transport, affording both hole andelectron mobilities up to 0.02 cm

Impact of Interfacial Microstructure on Charge Carrier Transport in Solution‐Processed Conjugated Polymer Field‐Effect Transistors

The surface roughness of a dielectric is precisely tuned, allowing a fine control solely over the interfacial microstructure in a semicrystalline semiconductor polymer film without affecting the morphology in the upper layers. The interfacial microstructure is found to have only a minor impact on the transport originating from bypassing of interfacial defects by the charge carriers.

Positive Magneto-LC Effect in Conjugated Spin-Bearing Hexabenzocoronene

The first neutral spin carrying hexabenzocoronene (HBC) derivative is described. The conjugated phenyl nitroxide substituted HBC with five alkyl chains exhibits a positive magneto-LC effect in columnar hexagonal liquid crystalline phase as probed by differential scanning calorimetry and electron paramagnetic resonance spectroscopy. Surprisingly, at 140 K the ΔMS = 2 transition can be observed indicating a thermally accessible triplet state between the neighboring molecules in the columnar arrangements.

Thermotropic Properties and Molecular Packing of Discotic Tristriazolotriazines with Rigid Substituents

Tristriazolotriazines with a threefold dialkoxyaryl substitution have been prepared by Huisgen reaction of cyanuric chloride and the corresponding tetrazoles. Although these dyes show a negative or inverted solvatochromism of the UV/Vis absorption, their fluorescence is strongly positive solvatochromic. These discotic fluorophores are also emissive in their solid state and in their broad liquid-crystalline mesophase. The structural study indicates that the thermotropic properties and organization of these systems can be well tuned by the steric demand of the aryl groups. Depending on the substituents, the compounds showed either a pure crystalline phase or a highly complex helical superstructure with a characteristic liquid-crystalline phase at elevated temperatures. Changing the steric demand of the attached aryls allowed controlling the discs arrangement within the columnar helix, which is of great importance for the molecular orbital overlap.

A Crown Ether Decorated Dibenzocoronene Tetracarboxdiimide Chromophore: Synthesis, Sensing, and Self-Organization

A macrocyclic dibenzocoronene tetracarboxdiimide containing two benzo-21-crown-7 groups has been synthesized. It shows liquid-crystalline behavior and selectively binds Pb(2+) or K(+) to form 1:2 complexes in solution. The complexation leads to a significant increase of fluorescence; the surface organization of discotic columnar structures, in the solid-state, can be controlled by selective ion binding.

Morphology Change and Improved Efficiency in Organic Photovoltaics via Hexa-peri-hexabenzocoronene Templates

The morphology of the active layer in organic photovoltaics (OPVs) is of crucial importance as it greatly influences charge generation and transport. A templating interlayer between the electrode and the active layer can change active layer morphology and influence the domain orientation. A series of amphiphilic interface modifiers (IMs) combining a hydrophilic polyethylene-glycol (PEG) oligomer and a hydrophobic hexabenzocoronene (HBC) were designed to be soluble in PEDOT:PSS solutions, and surface accumulate on drying. These IMs are able to self-assemble in solution. When IMs are deposited on top of a poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) film, they induce a morphology change of the active layer consisting of discotic fluorenyl-substituted HBC (FHBC) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM). However, when only small amounts (0.2 wt %) of IMs are blended into PEDOT:PSS, a profound change of the active layer morphology is also observed. Morphology changes were monitored by grazing incidence wide-angle X-ray scattering (GIWAXS), transmission electron microscopy (TEM), TEM tomography, and low-energy high-angle angular dark-field scanning transmission electron microscopy (HAADF STEM). The interface modification resulted in a 20% enhancement of power conversion efficiency.

Star-shaped conjugated molecules with oxa- or thiadiazole bithiophene side arms.

Star-shaped conjugated molecules, consisting of a benzene central unit symmetrically trisubstituted with either oxa- or thiadiazole bithiophene groups, were synthesized as promising molecules and building blocks for application in (opto)electronics and electrochromic devices. Their optical (Eg (opt)) as well as electrochemical (Eg (electro)) band gaps depended on the type of the side arm and the number of solubilizing alkyl substituents. Oxadiazole derivatives showed Eg (opt) slightly below 3 eV and by 0.2 eV larger than those determined for thiadiazole-based compounds. The presence of alkyl substituents in the arms additionally lowered the band gap. The obtained compounds were efficient electroluminophores in guest/host-type light-emitting diodes. They also showed a strong tendency to self-organize in monolayers deposited on graphite, as evidenced by scanning tunneling microscopy. The structural studies by X-ray scattering revealed the formation of supramolecular columnar stacks in which the molecules were organized. Differences in macroscopic alignment in the specimen indicated variations in the self-assembly mechanism between the molecules. The compounds as trifunctional monomers were electrochemically polymerized to yield the corresponding polymer network. As shown by UV/Vis-NIR spectroelectrochemical studies, these networks exhibited reversible electrochromic behavior both in the oxidation and in the reduction modes.

Controlling the Surface Organization of Conjugated Donor–Acceptor Polymers by their Aggregation in Solution

The aggregation of conjugated polymers is found to have a significant influence on the surface organization of deposited films. Difluorobenzothiadiazole-based polymers show a strong pre-aggregation in solution, but the addition of 1,2,4-trichlorobenzene efficiently reduces such aggregates, leading to the transition of the surface organization from edge- to face-on orientation in deposited films.

Improved charge carrier transport in ultrathin poly(3-hexylthiophene) films via solution aggregation

Field-effect transistors based on poly(3-hexylthiophene) (P3HT) bulk films exhibit maximum charge carrier mobilities of up to 0.1 cm2 V−1 s−1. However, reducing the thickness of the polymer film beyond 10 nm results in a significant deterioration of the charge transporting properties. In our work, we demonstrate a strategy towards ultrathin (i.e. thinner than 10 nm) polymer layers with charge carrier mobilities identical to bulk films. The improvement in conduction is related to aggregation of P3HT in solution allowing the formation of fibrils in the ultrathin films. Changing the molar mass of P3HT as well as varying the solvent type, aging time, and spin coating parameters resulted in layers with different thicknesses and fibrillar microstructures. The crystal packing and microstructure of the P3HT films, studied by atomic force microscopy and X-ray diffraction, were correlated with the transistor performance. It has been found that P3HT nanofibrils serve in the ultrathin films as pathways for charge carriers. Films of 8 nm thickness revealing a high density and a sufficient length of nanofibrils, along with pronounced internal crystallinity and long π-stacking coherence length, yield a mobility of 0.1 cm2 V−1 s−1. In this way, we demonstrated that controlling the microstructure of the active film in the ultrathin regime does not have to be at the expense of charge carrier mobility.