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Metal halide perovskite photodiodes (PPDs) offer high responsivity and broad spectral sensitivity, making them attractive for low-cost visible and near-infrared sensing. A significant challenge in achieving high detectivity in PPDs is lowering the dark current density (J D ) and noise current (i n ). This is commonly accomplished using charge-blocking layers to reduce charge injection. By analyzing the temperature dependence of J D for lead-tin based PPDs with different bandgaps and electron-blocking layers (EBL), we demonstrate that while EBLs eliminate electron injection, they facilitate undesired thermal charge generation at the EBL-perovskite interface. The interfacial energy offset between the EBL and the perovskite determines the magnitude and activation energy of J D . By increasing this offset we realized a PPD with ultralow J D and i n of 5 × 10 -8  mA cm -2 and 2 × 10 -14  A Hz -1/2 , respectively, and wavelength sensitivity up to 1050 nm, establishing a new design principle to maximize detectivity in perovskite photodiodes., (© 2021. The Author(s).)

Light-induced halide segregation hampers obtaining stable wide-band-gap solar cells based on mixed iodide-bromide perovskites. So far, the effect of prolonged illumination on the performance of mixed-halide perovskite solar cells has not been studied in detail. It is often assumed that halide segregation leads to a loss of open-circuit voltage. By simultaneously recording changes in photoluminescence and solar cell performance under prolonged illumination, we demonstrate that cells instead deteriorate by a loss of short-circuit current density and that the open-circuit voltage is less affected. The concurrent red shift, increased lifetime, and higher quantum yield of photoluminescence point to the formation of relatively emissive iodide-rich domains under illumination. Kinetic Monte Carlo simulations provide an atomistic insight into their formation via exchange of bromide and iodide, mediated by halide vacancies. Localization of photogenerated charge carriers in low-energy iodide-rich domains and subsequent recombination cause reduced photocurrent and red-shifted photoluminescence. The loss in photovoltaic performance is diminished by partially replacing organic cations by cesium ions. Ultrasensitive photocurrent spectroscopy shows that cesium ions result in a lower density of sub-band-gap defects and suppress defect growth under illumination. These defects are expected to play a role in the development and recovery of light-induced compositional changes., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Inflammatory bowel disease (IBD) is thought to be caused by an aberrant host response to the commensal enteric flora in genetically susceptible individuals. Dendritic cells (DCs) play a key role in the regulation of this response as they sample gut commensals. In healthy individuals DCs actively contribute to tolerance upon recognition of these resident bacteria, whereas in individuals with IBD, DCs will initiate an inflammatory response. To mimic the disease response in vitro, human monocyte-derived DCs were matured with E. coli causing the cells to produce high levels of the pro-inflammatory cytokine IL-12/IL-23p40 (p40) and low levels of the anti-inflammatory cytokine IL-10. A siRNA-based screening assay was developed and screened to identify potential therapeutic targets that shift this balance towards an immunosuppressive state with lower levels of p40 and higher levels of IL-10. The screening assay was optimized and quality controlled using non-targeting controls and positive control siRNAs targeting IL12B and TLR4 transcripts. In the primary screen, smartpool siRNAs were screened for reduction in p40 expression, induction of IL-10 levels, or increase in IL-10:p40 ratios without affecting cell viability. All potential targets were taken forward into a confirmation screen in a different DC donor in which four individual siRNAs per target were screened. At least two siRNAs per target should have an effect to be considered a valid target. This screen resulted in a concise list of ten genes, of which their role in DC maturation is currently being investigated., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)

Few semiconducting polymers are known that possess more than one semi-crystalline structure. Guidelines for rationalizing or creating polymorphism in these materials do not exist. Two different semi-crystalline polymorphs, β 1 and β 2 , and an amorphous α phase have recently been identified for alternating diketopyrrolopyrrole-quaterthiophene copolymers (PDPP4T). The polymorphs differ structurally by the π-π stacking distance, and electronically by the optical bandgap and charge carrier mobility. Here we investigate the corresponding terthiophene (PDPP3T) derivatives, to study the effect of the relative orientation of adjacent DPP units on the polymorphism. In PDPP3T, the relative orientation of DPP units alternates along the chain, while in PDPP4T it is constant. We show that the two polymorphs, β 1 and β 2 , can also be generated for a PDPP3T polymer in solution and thin film. Interestingly, compared to PDPP4T, more solvents can induce the two distinct semi-crystalline polymorphs for PDPP3T via a β 1  →  α  →  β 2 polymorphic transition., (© 2020 The Authors. Journal of Polymer Science published by Wiley Periodicals LLC.)

Parasitic optical absorption is one of the root causes of the moderate efficiency of metal halide perovskite solar cells (PSCs) with an opaque substrate configuration. Here, we investigate the reduction of these optical losses by using thin (7-10 nm), undoped, thermally evaporated 2,2',7,7'-tetrakis[ N , N -di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD), N , N '-di(1-naphthyl)- N , N '-diphenyl-(1,1'-biphenyl)-4,4'-diamine) (NPB), and tris(4-carbazoyl-9-ylphenyl)amine) (TCTA) hole transport layers (HTLs). Of these, NPB is found to offer the best compromise between efficiency and stability. In semitransparent n-i-p configuration PSCs with an indium tin oxide bottom and a MoO 3 /thin-Au/ZnS dielectric-metal-dielectric top electrode, NPB gives 14.9% and 10.7% efficiency for bottom and top illumination, respectively. The corresponding substrate-configuration PSC fabricated on an Au bottom electrode has 13.1% efficiency. Compared to a 14.0% efficient PSC with a thick spin-coated doped spiro-OMeTAD layer, the cell with NPB provides an improved short-circuit current density but has slightly lower open-circuit voltage and fill factor. Detailed analysis of the optical losses in the opaque devices demonstrates that evaporated NPB offers negligible parasitic absorption compared to solution-processed spiro-OMeTAD. The optical losses that remain are due to absorption and reflection of the transparent top electrode., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

Electron transport layers (ETLs) placed between the electrodes and a photoactive layer can enhance the performance of organic solar cells but also impose limitations. Most ETLs are ultrathin films, and their deposition can disturb the morphology of the photoactive layers, complicate device fabrication, raise cost, and also affect device stability. To fully overcome such drawbacks, efficient organic solar cells that operate without an ETL are preferred. In this study, a new small-molecule electron donor (H31) based on a thiophene-substituted benzodithiophene core unit with trialkylsilyl side chains is designed and synthesized. Blending H31 with the electron acceptor Y6 gives solar cells with power conversion efficiencies exceeding 13% with and without 2,9-bis[3-(dimethyloxidoamino)propyl]anthra[2,1,9-def:6,5,10-d'e'f ']diisoquinoline-1,3,8,10(2H,9H)-tetrone (PDINO) as the ETL. The ETL-free cells deliver a superior shelf life compared to devices with an ETL. Small-molecule donor-acceptor blends thus provide interesting perspectives for achieving efficient, reproducible, and stable device architectures without electrode interlayers., (© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH.)

The combination of narrow-bandgap diketopyrrolopyrrole (DPP) polymers and nonfullerene acceptors (NFAs) seems well-matched for solar cells that exclusively absorb in the near infrared but they rarely provide high efficiency. One reason is that processing of the active layer is complicated by the fact that DPP-based polymers are generally only sufficiently soluble in chloroform (CF), while NFAs are preferably processed from halogenated aromatic solvents. By using a ternary solvent system consisting of CF, 1,8-diiodooctane (DIO), and chlorobenzene (CB), the short-circuit current density is increased by 50% in solar cells based on a DPP polymer (PDPP5T) and a NFA (IEICO-4F) compared to the use of CF with DIO only. However, the open-circuit voltage and fill factor are reduced. As a result, the efficiency improves from 3.4 to 4.8% only. The use of CB results in stronger aggregation of IEICO-4F as inferred from two-dimensional grazing-incidence wide-angle X-ray diffraction. Photo- and electroluminescence and mobility measurements indicate that the changes in performance can be ascribed to a more aggregated blend film in which charge generation is increased but nonradiative recombination is enhanced because of reduced hole mobility. Hence, while CB is essential to obtain well-ordered domains of IEICO-4F in blends with PDPP5T, the morphology and resulting hole mobility of PDPP5T domains remain suboptimal. The results identify the challenges in processing organic solar cells based on DPP polymers and NFAs as near-infrared absorbing photoactive layers., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

The effect of the nature of the π-conjugated linker that is positioned between electron-deficient 2,5-dihydropyrrolo[3,4- c ]pyrrole-1,4-dione (DPP) and electron-rich dithieno[3,2- b :2',3'- d ]pyrrole (DTP) units in alternating DPP-DTP copolymers on the optical and electrochemical band gaps and the effective exciton binding energy is investigated for six different aromatic linkers. The optical band gap is related to the electron-donating properties of DTP and the electron-withdrawing properties of DPP but likewise strongly affected by the nature of the linker and varies between 1.13 and 1.80 eV for the six different linkers. The lowest optical band gaps are found for linkers that either raise the highest occupied molecular orbital or lower the lowest unoccupied molecular orbital most, while the highest optical band gap is found for phenyl linkers that have neither strong donating nor strong accepting properties. Along with the optical band gap, the electrochemical band gap also changes, but to a lesser extent from 1.46 to 1.89 eV. The effective exciton binding energy ( E b ), defined as the difference between the electrochemical and optical band gaps, decreases with an increasing band gap and reaches a minimum of 0.09 eV for the copolymer with the highest band gap, that is, with phenyl linkers. The reduction in E b with an increasing band gap is tentatively explained by a reduced electronic interaction between the DTP and DPP units when the HOMO localizes on DTP and the LUMO localizes on DPP. Support for this explanation is found in the molar absorption coefficient of the copolymers, which shows an overall decreasing trend with decreasing E b ., Competing Interests: The authors declare no competing financial interest., (© 2020 American Chemical Society.)

Inflammatory bowel disease (IBD) is a complex multi-factorial disease for which physiologically relevant in vitro models are lacking. Existing models are often a compromise between biological relevance and scalability. Here, we integrated intestinal epithelial cells (IEC) derived from human intestinal organoids with monocyte-derived macrophages, in a gut-on-a-chip platform to model the human intestine and key aspects of IBD. The microfluidic culture of IEC lead to an increased polarization and differentiation state that closely resembled the expression profile of human colon in vivo. Activation of the model resulted in the polarized secretion of CXCL10, IL-8 and CCL-20 by IEC and could efficiently be prevented by TPCA-1 exposure. Importantly, upregulated gene expression by the inflammatory trigger correlated with dysregulated pathways in IBD patients. Finally, integration of activated macrophages offers a first-step towards a multi-factorial amenable IBD platform that could be scaled up to assess compound efficacy at early stages of drug development or in personalized medicine.

The optical properties of two sets of donor-acceptor-donor molecules with terminal bithiophene donor units and a central diketopyrrolopyrrole (DPP) acceptor unit are studied. The two sets differ in the alkyl chains on the DPP, which are either branched at the α-carbon (3-pentyl) ( 1 - 4 ) or linear ( n -hexyl) ( 5 - 8 ). Within each set, the molecules differ by the absence or presence of n -hexyl chains on the terminal thiophene rings in the 3', 4', or 5' positions. While in solution, the optical spectra differ only subtly; they differ dramatically in the solid state. In contrast to 5 - 8 , 1 - 4 are nonplanar as a consequence of the sterically demanding 3-pentyl groups, which inhibit π-stacking of the DPP units. Using the crystal structures of 2 (brick layer stacking) and 6 (slipped stacking), we quantitatively explain the solid state absorption spectra. By computing the molecular transition charge density and solving the dispersion relation, the optical absorption of the molecules in the crystal is predicted and in agreement with experiments. For 2 , a single resonance frequency is obtained, while for 6 two transitions are seen, with the lower-energy transition being less intense. The results demonstrate how subtle changes in substitution exert large effects in optical properties., Competing Interests: The authors declare no competing financial interest., (© 2020 American Chemical Society.)

Introducing solubilizing α-branched alkyl chains on a poly(diketopyrrolopyrrole-alt-terthiophene) results in a dramatic change of the structural, optical, and electronic properties compared to the isomeric polymer carrying β-branched alkyl side chains. When branched at the α-position the alkyl substituent creates a steric hindrance that reduces the tendency of the polymer to π-π stack and endows the material with a much higher solubility in common organic solvents. The wider π-π stacking and reduced tendency to crystallize, evidenced from grazing-incidence wide-angle X-ray scattering, result in a wider optical band gap in the solid state. In solar cells with a fullerene acceptor, the α-branched isomer affords a higher open-circuit voltage, but an overall lower power conversion efficiency as a result of a too well-mixed nanomorphology. Due its reduced π-π stacking, the α-branched isomer fluoresces and affords near-infrared light-emitting diodes emitting at 820 nm., (© 2020 The Authors. Published by Wiley-VCH GmbH.)

Perovskite semiconductors hold a unique promise in developing multijunction solar cells with high-efficiency and low-cost. Besides design constraints to reduce optical and electrical losses, integrating several very different perovskite absorber layers in a multijunction cell imposes a great processing challenge. Here, we report a versatile two-step solution process for high-quality 1.73 eV wide-, 1.57 eV mid-, and 1.23 eV narrow-bandgap perovskite films. Based on the development of robust and low-resistivity interconnecting layers, we achieve power conversion efficiencies of above 19% for monolithic all-perovskite tandem solar cells with limited loss of potential energy and fill factor. In a combination of 1.73 eV, 1.57 eV, and 1.23 eV perovskite sub-cells, we further demonstrate a power conversion efficiency of 16.8% for monolithic all-perovskite triple-junction solar cells.

Two asymmetric thiophene (T)/pyridine (Py) flanked diketopyrrolopyrrole (DPP) polymers with a regiorandom and regioregular conjugated backbone are synthesized via a Stille polycondensation to investigate the effect of regioregularity on their optoelectronic properties and photovoltaic performance in fullerene-based polymer solar cells. Surprisingly, both polymers possess very similar optical bandgap, energy levels, and photovoltaic performance. These findings, combined with a factor of 19 reactivity difference between the two end groups of the asymmetric DPP monomer, intuitively suggest the formation of regular chain segments in the random polymer. However, by modeling the random polymerization reaction with a kinetic Monte Carlo (KMC) simulation, evidence is obtained for exclusive formation of a fully random polymer structure. UV-vis-NIR absorption spectra of three extended DPP chromophores, containing the donor segments (T-T-T, Py-T-Py, and Py-T-T) present in the regiorandom polymer, confirm that regioregularity of the backbone has a negligible influence on the optical properties., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

Photovoltaic devices that switch color depending on illumination conditions may find application in future smart window applications. Here a photochromic diarylethene molecule is used as sensitizer in a ternary bulk heterojunction blend, employing poly(4-butylphenyldiphenylamine) (poly-TPD) and [6,6]-phenyl-C 61 -butyric acid methyl ester (PC 61 BM) for the transport of holes and electrons, respectively. Sandwiched between two electrodes, the blend creates a photochromic photovoltaic device that changes color, light absorption, and photon-to-electron conversion efficiency in the visible spectral range after having been illuminated with UV light., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Hybrid organic-inorganic perovskite solar cells have recently emerged as one of the most promising low-cost photovoltaic technologies. The remarkable progress of perovskite photovoltaics is closely related to advances in interfacial engineering and development of charge selective interlayers. Herein, we present the synthesis and characterization of a fused azapolyheteroaromatic small molecule, namely anthradi-7-azaindole (ADAI), with outstanding performance as a hole-transporting layer in perovskite solar cells with inverted architecture. Its molecular arrangement, induced by hydrogen-bond-directed self-assembly, favors a suitable morphology of the perovskite layer, reducing the effects of recombination as revealed by light intensity dependence, photoluminescence, and electroluminescence studies., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Organic electrochemical transistors (OECTs) show great promise for flexible, low-cost, and low-voltage sensors for aqueous solutions. The majority of OECT devices are made using the polymer blend poly(ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), in which PEDOT is intrinsically doped due to inclusion of PSS. Because of this intrinsic doping, PEDOT:PSS OECTs generally operate in depletion mode, which results in a higher power consumption and limits stability. Here, a straightforward method to de-dope PEDOT:PSS using commercially available amine-based molecular de-dopants to achieve stable enhancement-mode OECTs is presented. The enhancement-mode OECTs show mobilities near that of pristine PEDOT:PSS (≈2 cm 2 V -1 s -1 ) with stable operation over 1000 on/off cycles. The electron and proton exchange among PEDOT, PSS, and the molecular de-dopants are characterized to reveal the underlying chemical mechanism of the threshold voltage shift to negative voltages. Finally, the effect of the de-doping on the microstructure of the spin-cast PEDOT:PSS films is investigated., (© 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

By analyzing the optical band gap and energy levels of seven different regioregular terpolymers in which two different electron-rich donor moieties are alternating with a common electron-deficient acceptor unit along the backbone, we establish a direct correlation with the properties of the corresponding binary copolymers in which one donor and one acceptor are combined. For this study, we use diketopyrrolopyrrole as the common acceptor and different π-conjugated aromatic oligomers as donors. We find that the optical band gap and frontier orbital energies of the terpolymers are the arithmetic average of those of the parent copolymers with remarkable accuracy. The same relationship is also found for the open-circuit voltage of the bulk heterojunction solar cells made with the ter- and copolymers in combination with [6,6]-phenyl-C 71 -butyric acid methyl ester. Comparison of these findings with data in the literature suggests that this is a universal rule that can be used as a tool when designing new π-conjugated polymers. The experimental results are supported by a semiempirical quantum chemical model that accurately describes the energy levels of the terpolymers after parametrization on the energy levels of the copolymers and also provides a theoretical explanation for the observed arithmetic relations., Competing Interests: The authors declare no competing financial interest., (Copyright © 2020 American Chemical Society.)

It remains a challenge to precisely tailor the morphology of polymer monolayers to control charge transport. Herein, the effect of the dissolution temperature (T dis ) is investigated as a powerful strategy for morphology control. Low T dis values cause extended polymer aggregation in solution and induce larger nanofibrils in a monolayer network with more pronounced π-π stacking. The field-effect mobility of the corresponding monolayer transistors is significantly enhanced by a factor of four compared to devices obtained from high T dis with a value approaching 1 cm 2  V -1  s -1 . Besides that, the solution kinetics reveal a higher growth rate of aggregates at low T dis , and filtration experiments further confirm that the dependence of the fibril width in monolayers on T dis is consistent with the aggregate size in solution. The generalizability of the T dis effect on polymer aggregation is demonstrated using three other conjugated polymer systems. These results open new avenues for the precise control of polymer aggregation for high-mobility monolayer transistors., (© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

A common bottleneck in any drug development process is finding sufficiently accurate models that capture key aspects of disease development and progression. Conventional drug screening models often rely on simple 2D culture systems that fail to recapitulate the complexity of the organ situation. In this study, we show the application of a robust high throughput 3D gut-on-a-chip model for investigating hallmarks of inflammatory bowel disease (IBD). Using the OrganoPlate platform, we subjected enterocyte-like cells to an immune-relevant inflammatory trigger in order to recapitulate key events of IBD and to further investigate the suitability of this model for compound discovery and target validation activities. The induction of inflammatory conditions caused a loss of barrier function of the intestinal epithelium and its activation by increased cytokine production, two events observed in IBD physiopathology. More importantly, anti-inflammatory compound exposure prevented the loss of barrier function and the increased cytokine release. Furthermore, knockdown of key inflammatory regulators RELA and MYD88 through on-chip adenoviral shRNA transduction alleviated IBD phenotype by decreasing cytokine production. In summary, we demonstrate the routine use of a gut-on-a-chip platform for disease-specific aspects modeling. The approach can be used for larger scale disease modeling, target validation and drug discovery purposes.

Poly(3,4-ethylenedioxythiophene) blended with polystyrenesulfonate and poly(styrenesulfonic acid), PEDOT:PSS, has found widespread use in organic electronics. Although PEDOT:PSS is commonly used in its doped electrically conducting state, the ability to efficiently convert PEDOT:PSS to its undoped nonconducting state is of interest for a wide variety of applications ranging from biosensors to organic neuromorphic devices. Exposure to aliphatic monoamines, acting as an electron donor and Brønsted-Lowry base, has been reported to be partly successful, but monoamines are unable to fully dedope PEDOT:PSS. Remarkably, some-but not all-polyamines can dedope PEDOT:PSS very efficiently to very low conductivity levels, but the exact chemical mechanism involved is not understood. Here, we study the dedoping efficacy of 21 different aliphatic amines. We identify the presence of two or more primary amines, which can participate in an intramolecular reaction, as the key structural motif that endows polyamines with high PEDOT:PSS dedoping strength. A multistep reaction mechanism, involving sequential electron transfer and deprotonation steps, is proposed that consistently explains the experimental results. Finally, we provide a simple method to convert the commonly used aqueous PEDOT:PSS dispersion into a precursor formulation that forms fully dedoped PEDOT:PSS films after spin coating and subsequent thermal annealing., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

Polymorphism of organic semiconducting materials exerts critical effects on their physical properties such as optical absorption, emission and electrical conductivity, and provides an excellent platform for investigating structure-property relations. It is, however, challenging to efficiently tune the polymorphism of conjugated polymers in aggregated, semi-crystalline phases due to their conformational freedom and anisotropic nature. Here, two distinctly different semi-crystalline polymorphs (β 1 and β 2 ) of a low-bandgap diketopyrrolopyrrole polymer are formed through controlling the solvent quality, as evidenced by spectroscopic, structural, thermal and charge transport studies. Compared to β 1 , the β 2 polymorph exhibits a lower optical band gap, an enhanced photoluminescence, a reduced π-stacking distance, a higher hole mobility in field-effect transistors and improved photocurrent generation in polymer solar cells. The β 1 and β 2 polymorphs provide insights into the control of polymer self-organization for plastic electronics and hold potential for developing programmable ink formulations for next-generation electronic devices.

Homocoupling of monomers in a palladium-catalyzed copolymerization of donor-acceptor polymers affects the perfect alternating structure and may deteriorate the performance of such materials in solar cells. Here we investigate the effect of homocoupling bis(trialkylstannyl)-thiophene and -bithiophene monomers in two low band gap poly(diketopyrrolopyrrole- alt -oligothiophene) polymers by deliberately introducing extended oligothiophene defects in a controlled fashion. We find that extension of the oligothiophene by one or two thiophenes and creating defects up to at least 10% does not significantly affect the opto-electronic properties of the polymers or their photovoltaic performance as electron donor in solar cells in combination with [6,6]-phenyl C 71 butytic acid methyl ester as acceptor. By using model reactions, we further demonstrate that for the optimized synthetic protocol and palladium-catalyst system the naturally occurring defect concentration in the polymers is expected to be less than 0.5%., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Singlet fission in pentacene creates two triplet excitons per absorbed photon. In a solar cell, each triplet can generate an electron-hole pair, and hence, external quantum efficiencies exceeding 100% have been reported for pentacene-fullerene solar cells. The energetics of this process are intriguing because the minimum photon energy loss, defined as the energy difference between the (triplet) exciton state and the open-circuit voltage, is less than 0.5 eV and distinctively smaller than that in most organic donor-acceptor solar cells. To investigate the energetics of this process, we analyze the effect of the energy of the lowest unoccupied molecular orbital (LUMO) for different fullerene derivatives. With the LUMO energy becoming less negative, the open-circuit voltage increases and charge generation decreases. For all but one of the fullerenes tested, the charge-transfer state energy is distinctively higher than the pentacene triplet energy, revealing that charge generation via singlet fission is actually endergonic. An elementary Marcus model for the rate of electron transfer provides a qualitative description of the experimental trends, in accordance with an endergonic charge transfer. Considering that charge generation from triplet states is endergonic, involvement of pentacene singlet states, either from direct photoexcitation or via triplet-triplet annihilation, cannot be excluded., Competing Interests: The authors declare no competing financial interest.

Developing effective methods to make efficient bulk-heterojunction polymer solar cells at roll-to-roll relevant active layer thickness is of significant importance. We investigate the effect of fullerene content in polymer:fullerene blends on the fill factor (FF) and on the performance of thick-film solar cells for four different donor polymers PTB7-Th, PDPP-TPT, BDT-FBT-2T, and poly[5,5'-bis(2-butyloctyl)-(2,2'-bithiophene)-4,4'-dicarboxylate- alt-5,5'-2,2'-bithiophene] (PDCBT). At a few hundreds of nanometers thickness, increased FFs are observed in all cases and improved overall device performances are obtained except for PDCBT upon increasing fullerene content in blend films. This fullerene content effect was studied in more detail by electrical and morphological characterization. The results suggest enhanced electron mobility and suppressed bimolecular recombination upon increasing fullerene content in thick polymer:fullerene blend films, which are the result of larger fullerene aggregates and improved interconnectivity of the fullerene phases that provide continuous percolating pathways for electron transport in thick films. These findings are important because an effective and straightforward method that enables fabricating efficient thick-film polymer solar cells is desirable for large-scale manufacturing via roll-to-roll processing and for multijunction devices.

The effect of gradually replacing the branched alkyl side chains of a diketopyrrolopyrrole (DPP) conjugated polymer by linear side chains containing branched siloxane end groups on the photovoltaic performance of blends of these polymers with a common fullerene acceptor is investigated. With an increasing proportion of siloxane side chains, the molecular weight and solubility of the polymers decreases. While the siloxane containing polymers exhibit a higher hole mobility in field-effect transistors, their performance in solar cells is less than the polymer with only alkyl sides chains. Using grazing-incidence wide-angle X-ray scattering, transmission electron microscopy, and fluorescence spectroscopy we identify two main reasons for the reduced performance of siloxane containing polymers in solar cells. The first one is a somewhat coarser phase-separated morphology with slightly wider polymer fibers. This is unexpected as often the fiber width is inversely correlated with polymer solubility. The second one is stronger non-radiative decay of the pristine polymers containing siloxane side chains., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The efficiency of organic solar cells can benefit from multijunction device architectures, in which energy losses are substantially reduced. Herein, recent developments in the field of solution-processed multijunction organic solar cells are described. Recently, various strategies have been investigated and implemented to improve the performance of these devices. Next to developing new materials and processing methods for the photoactive and interconnecting layers, specific layers or stacks are designed to increase light absorption and improve the photocurrent by utilizing optical interference effects. These activities have resulted in power conversion efficiencies that approach those of modern thin film photovoltaic technologies. Multijunction cells require more elaborate and intricate characterization procedures to establish their efficiency correctly and a critical view on the results and new insights in this matter are discussed. Application of multijunction cells in photoelectrochemical water splitting and upscaling toward a commercial technology is briefly addressed., (© 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The packing mode of small-molecular semiconductors in thin films is an important factor that controls the performance of their optoelectronic devices. Designing and changing the packing mode by molecular engineering is challenging. Three structurally related diketopyrrolopyrrole (DPP)-based compounds were synthesized to study the effect of replacing C-C bonds by isoelectronic dipolar B←N bonds. By replacing one of the bridging C-C bonds on the peripheral fluorene units of the DPP molecules by a coordinative B←N bond and changing the B←N bond orientation, the optical absorption, fluorescence, and excited-state lifetime of the compounds can be tuned. The substitution alters the preferential aggregation of the molecules in the solid state from H-type (for C-C) to J-type (for B←N). Introducing B←N bonds thus provides a subtle way of controlling the packing mode. The photovoltaic properties of the compounds were evaluated in bulk heterojunctions with a fullerene acceptor and showed moderate performance as a consequence of suboptimal morphologies, bimolecular recombination, and triplet-state formation., (© 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Photovoltaic retinal prostheses show great potential to restore sight in patients suffering from degenerative eye diseases by electrical stimulation of the surviving neurons in the retinal network. Herein, organic photodiodes (OPDs) sensitive to near-infrared (NIR) light are evaluated as photovoltaic pixels for future application in retinal prostheses. Single-junction and tandem OPDs are compared. In the latter, two nominally identical single-junction cells are processed on top of each other, effectively doubling the open-circuit voltage (V OC ). Both single-junction and tandem OPD micropixels can deliver the required charge to stimulate neurons under pulsed NIR light at physiologically safe intensities when connected to stimulating microelectrodes in a physiological saline solution. However, only tandem OPD pixels can cover the entire charge per pulse neural stimulation window due to their higher V OC (≈1.4 V). This demonstrates the viability of high-resolution retinal prostheses based on flexible OPD arrays., (© 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We investigate the effect of fluorination on the photovoltaic properties of an alternating conjugated polymer composed of 4,8-di-2-thienylbenzo[1,2- b :4,5- b ']dithiophene (BDT) and 4,7-bis([2,2'-bithiophen]-5-yl)-benzo-2-1-3-thiadiazole (4TBT) units in bulk-heterojunction solar cells. The unsubstituted and fluorinated polymers afford very similar open-circuit voltages and fill factor values, but the fluorinated polymer performed better due to enhanced aggregation which provides a higher photocurrent. The photovoltaic performance of both materials improved upon thermal annealing at 150-200 °C as a result of a significantly increased fill factor and open-circuit voltage, counteracted by a slight loss in photocurrent. Detailed studies of the morphology, light intensity dependence, external quantum efficiency and electroluminescence allowed the exploration of the effects of fluorination and thermal annealing on the charge recombination and the nature of the donor-acceptor interfacial charge transfer states in these films.

A monolithic two-terminal solution-processed quadruple junction polymer solar cell in an n-i-p (inverted) configuration with four complementary polymer:fullerene active bulk-heterojunction layers is presented. The subcells possess different optical bandgaps ranging from 1.90 to 1.13 eV. Optical modeling using the transfer matrix formalism enables prediction of the fraction of absorbed photons from sunlight in each subcell and determine the optimal combination of layer thicknesses. The quadruple junction cell features an open-circuit voltage of 2.45 V and has a power conversion efficiency of 7.6%, only slightly less than the modeled value of 8.2%. The external quantum efficiency spectrum, determined with appropriate light and voltage bias conditions, exhibits in general an excellent agreement with modeled spectrum. The device performance is presently limited by bimolecular recombination, which prevents using thick photoactive layers that could absorb light more efficiently., (© 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

All-polymer solar cells (all-PSCs) composed of conjugated polymers as both donor and acceptor components in bulk heterojunction photoactive layers have attracted increasing attention. However, it is a big challenge to achieve optimal morphology in polymer:polymer blends. In response, we report herein a new strategy to adjust the nanoscale organization for all-PSCs. Specifically, side chain engineering of the well-known naphthalene diimide (NDI)-based polymer N2200 is modulated by introducing a fraction of linear oligoethylene oxide (OE) side chains to replace branched alkyl chains on the NDI units and by synthesizing a series of NDI-based polymer acceptors NOE x, where x is the percentage of OE chain substituted NDI units relative to total NDI units. Compared to the reference polymer NOE0, OE-chain-containing polymer NOE10 offers a much higher power conversion efficiency (PCE) of 8.1% with a record high fill factor (FF) of 0.75 in all-PSCs. Moreover, the NOE10-based all-PSC exhibits excellent long-term and thermal stabilities with >97% of the initial PCE being maintained after 300 h of aging at 65 °C. This work demonstrates an effective morphology optimization strategy to achieve highly efficient and stable all-PSCs and shows the excellent potential of NOE10 as an alternative to commercially available acceptor polymers N2200.

Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is frequently used as hole transport layer in planar p-i-n perovskite solar cells. Here we show that processing of a metal halide perovskite layer on top of PEDOT:PSS via spin coating of a precursor solution chemically reduces the oxidation state of PEDOT:PSS. This reduction leads to a lowering of the work function of the PEDOT:PSS and the perovskite layer on top of it. As a consequence, the solar cells display inferior performance with a reduced open-circuit voltage and a reduced short-circuit current density, which increases sublinearly with light intensity. The reduced PEDOT:PSS can be re-oxidized by thermal annealing of the PEDOT:PSS/perovskite layer stack in the presence of oxygen. As a consequence, thermal annealing of the perovskite layer in air provides solar cells with increased open-circuit voltage, short-circuit current density and high efficiency.

A new class of subnaphthalocyanines bearing various peripheral and axial substituents have been synthesized for use as electron acceptors in solution-processed bulk-heterojunction polymer solar cells. The resulting solar cells exhibit modest photovoltaic performance with contributions from both the polymer donor and subnaphthalocyanine acceptor to the photocurrent., (© 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The straightforward synthesis and photophysical properties of a new series of heteroleptic iridium(III) bis(2-arylimidazole) picolinate complexes are reported. Each complex has been characterized by nuclear magnetic resonance, UV-vis, cyclic voltammetry, and photoluminescent angle dependency, and the emissive properties of each are described. The preferred orientation of transition dipoles in emitter/host thin films indicated more preferred orientation than homoleptic complex Ir(ppy) 3 ., Competing Interests: The authors declare no competing financial interest.

The efficient synthesis of a new solution-processable n-type conjugated polymer network (PNT1) is reported through palladium-catalyzed Stille cross-coupling reaction conditions following the A 3 + B 2 synthetic approach. A benzo[1,2-b:3,4-b':5,6-b″]trithiophene derivative is used as the A 3 knot and an alkyl functionalized naphthalenediimide is utilized as the B 2 linker. The thermal, optical, and electrochemical properties are examined in detail, showing high thermal stability, absorbance in the visible part of the solar spectrum, and reversible reduction characteristics similar to those of the fullerene derivative [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM). PNT1 is employed as the electron acceptor in solution-processed bulk heterojunction organic solar cells, demonstrating the potential of this new type of materials for optoelectronic applications., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of "double-cable" conjugated polymers were developed for application in efficient single-component polymer solar cells, in which high quantum efficiencies could be achieved due to the optimized nanophase separation between donor and acceptor parts. The new double-cable polymers contain electron-donating poly(benzodithiophene) (BDT) as linear conjugated backbone for hole transport and pendant electron-deficient perylene bisimide (PBI) units for electron transport, connected via a dodecyl linker. Sulfur and fluorine substituents were introduced to tune the energy levels and crystallinity of the conjugated polymers. The double-cable polymers adopt a "face-on" orientation in which the conjugated BDT backbone and the pendant PBI units have a preferential π-π stacking direction perpendicular to the substrate, favorable for interchain charge transport normal to the plane. The linear conjugated backbone acts as a scaffold for the crystallization of the PBI groups, to provide a double-cable nanophase separation of donor and acceptor phases. The optimized nanophase separation enables efficient exciton dissociation as well as charge transport as evidenced from the high-up to 80%-internal quantum efficiency for photon-to-electron conversion. In single-component organic solar cells, the double-cable polymers provide power conversion efficiency up to 4.18%. This is one of the highest performances in single-component organic solar cells. The nanophase-separated design can likely be used to achieve high-performance single-component organic solar cells.

The efficiency of organic light emitting diodes (OLEDs) can be improved by controlling the orientation of the transition dipole moment of the emitters. Currently, no effective methods exist for orienting the transition dipole moments in solution processed active layers for OLEDs. We investigate the orientation of the transition dipole moment of small molecular emitters in a host matrix of poly(9,9-dioctylfluorene) (PFO) by means of angle dependent luminescence intensity measurements. The polymer chains of the host orient predominantly in the plane of the film. Fluorescent p -phenylenevinylene oligomers with 6 and 7 repeat units (OPV6, OPV7) are found to also orient preferentially horizontally. The orientation of the emitters can be improved by thermal annealing with up to 90% of transition dipole moments oriented in the plane of the film. The phosphorescent emitter Ir(MDQ) 2 (acac) shows a degree of horizontal orientation in the polymeric host matrix lower than that which is observed for oligomers, but as high as is observed for the same emitter in evaporated layers. A carbazole derivative capable of thermally activated delayed fluorescence shows a small preference for vertical orientation within the polymer host. The strong orientation of OPV6 and OPV7 in the oriented polymer host is rationalized in terms of their high aspect ratios. The use of PFO as host material in host/guest systems allows achieving horizontal orientation of transition dipole moments in solution processed oligomers and small molecular emitters.

The effects of cold and hot processing on the performance of polymer-fullerene solar cells are investigated for diketopyrrolopyrrole (DPP) based polymers that were specifically designed and synthesized to exhibit a strong temperature-dependent aggregation in solution. The polymers, consisting of alternating DPP and oligothiophene units, are substituted with linear and second position branched alkyl side chains. For the polymer-fullerene blends that can be processed at room temperature, hot processing does not enhance the power conversion efficiencies compared to cold processing because the increased solubility at elevated temperatures results in the formation of wider polymer fibres that reduce charge generation. Instead, hot processing seems to be advantageous when cold processing is not possible due to a limited solubility at room temperature. The resulting morphologies are consistent with a nucleation-growth mechanism for polymer fibres during drying of the films.

Polymer solar cells based on PDPP5T and PCBM as donor and acceptor materials, respectively, were processed from aqueous nanoparticle dispersions. Careful monitoring and optimization of the concentration of free and surface-bound surfactants in the dispersion, by measuring the conductivity and ζ-potential, is essential to avoid aggregation of nanoparticles at low concentration and dewetting of the film at high concentration. The surfactant concentration is crucial for creating reproducible processing conditions that aid in further developing aqueous nanoparticle processed solar cells. In addition, the effects of adding ethanol, of aging the dispersion, and of replacing [60]PCBM with [70]PCBM to enhance light absorption were studied. The highest power conversion efficiencies (PCEs) obtained are 2.0% for [60]PCBM and 2.4% for [70]PCBM-based devices. These PCEs are limited by bimolecular recombination of photogenerated charges. Cryo-TEM reveals that the two components phase separate in the nanoparticles, forming a PCBM-rich core and a PDPP5T-rich shell and causing a nonoptimal film morphology.

Six poly(phenylene- alt -dithienobenzothiadiazole)-based polymers have been synthesized for application in polymer-fullerene solar cells. Hydrogen, fluorine, or nitrile substitution on benzo-thiadiazole and alkoxy or ester substitution on the phenylene moiety are investigated to reduce the energy loss per converted photon. Power conversion efficiencies (PCEs) up to 6.6% have been obtained. The best performance is found for the polymer-fullerene combination with distinct phase separation and crystalline domains. This improves the maximum external quantum efficiency for charge formation and collection to 66%. The resulting higher photocurrent compensates for the relatively large energy loss per photon ( E loss = 0.97 eV) in achieving a high PCE. By contrast, the poly-mer that provides a reduced energy loss ( E loss = 0.49 eV) gives a lower photocurrent and a reduced PCE of 1.8% because the external quantum efficiency of 17% is limited by a suboptimal morphology and a reduced driving force for charge transfer.

Antimicrobial proteins and peptides (AMPs) are a central component of the antibacterial activity of airway epithelial cells. It has been proposed that a decrease in antibacterial lung defense contributes to an increased susceptibility to microbial infection in smokers and patients with chronic obstructive pulmonary disease (COPD). However, whether reduced AMP expression in the epithelium contributes to this lower defense is largely unknown. We investigated the bacterial killing activity and expression of AMPs by air-liquid interface-cultured primary bronchial epithelial cells from COPD patients and non-COPD (ex-)smokers that were stimulated with nontypeable Haemophilus influenzae (NTHi). In addition, the effect of cigarette smoke on AMP expression and the activation of signaling pathways was determined. COPD cell cultures displayed reduced antibacterial activity, whereas smoke exposure suppressed the NTHi-induced expression of AMPs and further increased IL-8 expression in COPD and non-COPD cultures. Moreover, smoke exposure impaired NTHi-induced activation of NF-κB, but not MAP-kinase signaling. Our findings demonstrate that the antibacterial activity of cultured airway epithelial cells induced by acute bacterial exposure was reduced in COPD and suppressed by cigarette smoke, whereas inflammatory responses persisted. These findings help to explain the imbalance between protective antibacterial and destructive inflammatory innate immune responses in COPD., (© 2017 The Author(s) Published by S. Karger AG, Basel.)

Novel wide-bandgap semiconducting polymers are designed and synthesized for multijunction polymer solar cell (PSC) applications. In single-junction PSCs, BDT-FBT-2T exhibits efficiencies exceeding 6.5% for active layer thicknesses between 90 and 250 nm, with the highest efficiency of 7.7% at 100 and 250 nm. This enables tandem PSCs to be created with an efficiency of 8.9%., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)