a series of reasons. First of all, the power conversion efficiencies (PCEs) are still low compared to silicon photovoltaics or perovskite photovoltaics. At the laboratory level, the PCEs of small area devices are improving, [9] but with their best still below 20%, [10,11] despite the fact that the recent breakthrough discovery of non-fullerene acceptors (NFAs) [12,13] has almost doubled the values achieved within the last four years. Second, although important progress on controlling degradation has been made, [14] the device stability still needs to be improved to provide reliable and marketable products. Third, the synthetic complexity [15][16][17][18] of the best performing active layer materials (both donor and acceptors) is usually relatively high, which translates into high material's production costs. Fourth, the interfacial engineering is still at the research stage [19] and a defined scalable device architecture has not yet been fully established. Last, but not least, the scalability of cells to modules with continuous printing/coating techniques has been demonstrated, [20,21] but in practice, formulating the active inks at an industrial level is not an easy task. Problems related to photoactive materials solubility, solution viscosities, and films' wettability have to be carefully approached to achieve optimal process conditions, suitable for roll-to-roll (R2R) manufacturing.One issue in particular is worth considering: to achieve homogeneous, pinhole-free film over large areas and at high printing speed, the active-layer thickness needs to be high enough. A thickness above 200 nm is considered suitable, [22,23] but this point is in conflict with the possibility for the charge carriers to effectively reach the electrode contacts while avoiding recombinations. Charge-carrier mobilities of organic semiconductors are in fact not very high, even in the best of cases. It is known that optimal PCEs of NFA-based polymer solar cells are achieved with thicknesses of around 90-120 nm, [24] and then decrease when thickness is increased (Figure 1). Together with the limitations in annealing temperatures and durations, the need to substitute evaporated interlayers and electrodes with printable alternatives and the need for a high thickness of the active (absorbing) layer is one of the main reasons for the PCE decrease in the transition from small-area laboratory devices to large-area modules by R2R processes.Organic photovoltaics (OPV) has been considered for a long time a promising emerging solar technology. Currently, however, market shares of OPV are practically non-existent. A detailed meta-analysis of the literature published until mid-2021 is presented, focusing on one of the remaining issues that need to be addressed to translate the recent remarkable progress, obtained in devices' performance at lab-scale level, into the requirements able to boost the manufacturing-scale production. Namely, the active layer's thickness is referred to, which, together with device efficiency and stability, represents one of th...
We synthetized a new rod-coil block copolymer (BCP) based on the semiconducting polymerpoly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl}) (PTB7) and poly-4-vinylpyridine (P4VP), tailored to produce water-processable nanoparticles (WPNPs) in blend with phenyl-C71-butyric acid methyl ester (PC71BM). The copolymer PTB7-b-P4VP was completely characterized by means of two-dimensional nuclear magnetic resonance (2D-NMR), matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry (MS), size-exclusion chromatography (SEC), and differential scanning calorimetry (DSC) to confirm the molecular structure. The WPNPs were prepared through an adapted miniemulsion approach without any surfactants. Transmission electron microscopy (TEM) images reveal the nano-segregation of two active materials inside the WPNPs. The nanostructures appear spherical with a Janus-like inner morphology. PTB7 segregated to one side of the nanoparticle, while PC71BM segregated to the other side. This morphology was consistent with the value of the surface energy obtained for the two active materials PTB7-b-P4VP and PC71BM. The WPNPs obtained were deposited as an active layer of organic solar cells (OSCs). The films obtained were characterized by UV-Visible Spectroscopy (UV-vis), atomic force microscopy (AFM), and grazing incidence X-ray diffraction (GIXRD). J-V characteristics of the WPNP-based devices were measured by obtaining a power conversion efficiency of 0.85%. Noticeably, the efficiency of the WPNP-based devices was higher than that achieved for the devices fabricated with the PTB7-based BCP dissolved in chlorinated organic solvent.
Core cross-linked star (CCS) copolymers were prepared by reversible addition−fragmentation chain-transfer polymerization according to the arm-first technique and studied as viscosity index improvers for the application in hydraulic lubricants. A one-pot two-step synthetic procedure was optimized: starting from PMA arms with a precisely controlled structure and three different molecular weights and using different amounts of either divinylbenzene or ethylene glycol dimethacrylate as cross-linking agents, CCS copolymers with a high star yield (63 to 88%) were obtained. CCS copolymers present weight average molecular weight values ranging from 130,000 to 420,000 g mol −1 and a number of arms comprised between 4 and 13. All samples were employed, without any purification step, in the preparation of model lubricant formulations for hydraulic fluid applications. A good compromise between viscosity index improvement and capability to resist chain breaking reactions was obtained for CCS copolymers with target molecular weight for the PMA arms of 20,000 g mol −1 . Improved performances with respect to a commercial additive were obtained.
Bulk heterojunction organic solar cells (BHJs) are competitive within the emerging photovoltaic technologies for solar energy conversion because of their unique advantages. Their development has been boosted recently by the introduction of nonfullerene electron acceptors (NFAs), to be used in combination with a polymeric electron donor in the active layer composition. Many of the recent advances in NFAs are attributable to the class of fused-ring electron acceptors (FREAs), which is now predominant, with one of the most notable examples being formed with a fused five-member-ring indaceno[1,2-b:5,6-b′]dithiophene (IDT) core. Here, we propose a novel and more sustainable synthesis for the IDT core. Our approach bypasses tin derivatives needed in the Stille condensation, whose byproducts are toxic and difficult to dispose of, and it makes use of cascade reactions, effectively reducing the number of synthetic steps.
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