Organic photovoltaics (OPVs) promise cheap and flexible solar energy. Whereas light generates free charges in silicon photovoltaics, excitons are normally formed in organic semiconductors due to their low dielectric constants, and require molecular heterojunctions to split into charges. Recent record efficiency OPVs utilise the small molecule, Y6, and its analogues, which – unlike previous organic semiconductors – have low band-gaps and high dielectric constants. We show that, in Y6 films, these factors lead to intrinsic free charge generation without a heterojunction. Intensity-dependent spectroscopy reveals that 60–90% of excitons form free charges at AM1.5 light intensity. Bimolecular recombination, and hole traps constrain single component Y6 photovoltaics to low efficiencies, but recombination is reduced by small quantities of donor. Quantum-chemical calculations reveal strong coupling between exciton and CT states, and an intermolecular polarisation pattern that drives exciton dissociation. Our results challenge how current OPVs operate, and renew the possibility of efficient single-component OPVs.

as printing fabrication, light weight, flexibility, low toxicity, and short energy payback time. The fused-ring electron acceptors (FREAs) pioneered by the Zhan group have broken through the bottleneck of fullerene acceptors, [1][2][3] and OSCs have achieved revolutionary breakthrough recently. [1][2][3][4][5][6] To date, power conversion efficiencies (PCEs) of FREA-based OSCs have reached 18-19%. [7][8][9][10] Among the diverse FREAs, Y6 (chemical structure shown in Figure S1, Supporting Information) and its derivatives have been widely studied recently due to their high photovoltaic performance. [11][12][13][14] Since most organic semiconductors have low dielectric constants (ε ≈ 3-4), [15] Frenkel excitons with high binding energies (E B ) rather than free charges are generated intrinsically upon photoexcitation. Donor (D)/acceptor (A) interfaces that can provide a driving force for exciton dissociation are essential. [16,17] According to the general consensus developed in fullerene-based OSCs, a bulk heterojunction (BHJ) with D/A phase separation size of around 10-20 nm was the optimal morphology for efficient exciton dissociation and charge transport. [18] Accordingly, most high-efficiency optimized OSCs have In contrast to classical bulk heterojunction (BHJ) in organic solar cells (OSCs), the quasi-homojunction (QHJ) with extremely low donor content (≤10 wt.%) is unusual and generally yields much lower device efficiency.Here, representative polymer donors and nonfullerene acceptors are selected to fabricate QHJ OSCs, and a complete picture for the operation mechanisms of high-efficiency QHJ devices is illustrated. PTB7-Th:Y6 QHJ devices at donor:acceptor (D:A) ratios of 1:8 or 1:20 can achieve 95% or 64% of the efficiency obtained from its BHJ counterpart at the optimal D:A ratio of 1:1.2, respectively, whereas QHJ devices with other donors or acceptors suffer from rapid roll-off of efficiency when the donors are diluted. Through device physics and photophysics analyses, it is observed that a large portion of free charges can be intrinsically generated in the neat Y6 domains rather than at the D/A interface. Y6 also serves as an ambipolar transport channel, so that hole transport as also mainly through Y6 phase. The key role of PTB7-Th is primarily to reduce charge recombination, likely assisted by enhancing quadrupolar fields within Y6 itself, rather than the previously thought principal roles of light absorption, exciton splitting, and hole transport.

Six new lamellarin sulfates (1–6) were isolated from the methanolic extract of the Pacific tunicate Didemnum ternerratum, collected from the Kingdom of Tonga. Mass spectrometric molecular networking through the GNPS platform was used to target the isolation of 1–6. Planar structures were elucidated through a combination of NMR and MS experiments. Through comparison of experimental and calculated ECD spectra, the absolute configurations of atropisomers 2–5 were determined, with their energetic barriers to racemization also determined computationally. The cytotoxicity of the compounds was tested against the human colon carcinoma cell line HCT-116, where lamellarin D-8-sulfate (5) exhibited moderate activity with an IC50 of 9.7 μM.

Carboxylate-functionalised polymers of intrinsic microporosity (C-PIMs) are highly desirable materials for membrane separation applications. The recently reported method to afford C-PIMs was via an extensive base hydrolysis process requiring 360 h. Herein, a novel and effective method to convert PIM-CONH2 to C-PIM using nitrous acid was studied. The chemical structure of C-PIM was characterised by 1H NMR, 13C NMR, FTIR, elemental analysis, UV-Vis, TGA and TGA-MS. Complete conversion from amide to carboxylic acid groups was confirmed. Decarboxylation of C-PIM was also successfully studied by TGA-MS for the first time, with a loss of m/z 44 amu (CO2) observed at the first degradation stage. TGA also revealed decreased thermal stability of C-PIM relative to PIM-CONH2 under both N2 and air atmosphere. Gel permeation chromatography (GPC) analysis showed continuous molecular weight degradation of C-PIM with extended reaction time. Aromatic nitration was also observed as a side reaction in some cases.

The solid state supramolecular interactions of diketopyrrolopyrrole derivatives (DPPs) and their correlation with thin film optical properties are of particular interest because of the applications of these materials in organic...

Low energetic disorder enables the accurate and high-speed prediction of exciton diffusion parameters in a non-fullerene acceptor.

Chiral thiophene-diketopyrrolopyrrole derivatives have been synthesised to investigate the potential of stereochemistry and symmetry as a means of modulating properties by influencing self-assembly of these purely organic materials. In particular, derivatives of diketopyrrolopyrrole were employed because of their proven interest as dyes, especially for organic solar cells. The natural product myrtenal was used as the source of stereochemistry, introduced through a Kröhnke reaction of a thiophene-bearing pyridinium salt and diketopyrrolopyrroles were prepared through Suzuki coupling with this chiral moiety at one end only as well as at both ends. Absorption spectroscopy and electrochemistry confirmed the potential suitability of the compounds for photovoltaic devices. The nanostructures formed by the compounds have been probed with circular dichroism spectroscopy in solution and in films. It is shown that a chiral C symmetric molecule assembles in solution giving a strong circular dichroic signal while as a film this optical activity is nulled, whereas an asymmetric homologue is most optically active as a thin film. The X-ray crystal structure of the asymmetric compound shows a polar order of the molecules that might explain this observation. The lack of optical activity in solution is very likely a result of the high solubility of the compound. The results reaffirm the sensitivity of circular dichroism spectroscopy to inter-chromophore organisation, whereas absorption spectroscopy in the visible region reveals only slight changes to the bands. The differing order in the compounds also affects their performance in bulk heterojunction photovoltaic devices. Atomic force microscopy of the blended thin films with the fullerene derivative usually employed (PC BM) showed that smooth and well mixed films were achieved, with the conditions required during spin coating depending greatly on the derivative, because of their differing solubility. The apparently better performance of the symmetrical compound (although with very low efficiency) is probably a result of the alignment of the molecules inferred by the circular dichroism experiments, whereas the asymmetric compound presumably adopts a twisted supramolecular organisation.

2-Bromo-1,3-butadienes are demonstrated to be effective substrates for tandem Diels–Alder/transition metal cross-coupling reaction sequences. Intermolecular cycloaddition of a 2-bromo-1,3-diene with activated dienophiles proceeded under Lewis acid catalysis in generally high yields with good to excellent endo diastereoselectivity. The resulting vinyl bromide cycloadducts underwent subsequent Stille and Suzuki cross-couplings under standard conditions in good yields. Both the Diels–Alder and cross-coupling steps were highly tolerant of a range of functionalities and protecting groups. The use of the bromine substituent as both a cycloaddition directing group and cross-coupling nucleofuge avoids extra steps required to install and remove the more commonly used silyl enol ethers and enol sulfonates for each transformation and gives full control of the alkene regiochemistry throughout the reaction sequence. The 2-bromo-1,3-dienes were conveniently prepared in three steps from readily available aldehydes and established as hydrolytically stable and practical synthetic intermediates.