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While it is widely recognized that microstructure plays an important role in the performance of organic photovoltaics (OPV), systematic studies are often challenging, as varying the molecular packing through typical chemical means (such as sidechain tuning) often affects the molecular energy levels, thus preventing a clear correlation. In this work we present the synthesis of three perylene imide (PI) based electron acceptors with almost identical energy levels, but distinct packing tendencies. We confirm our initial hypothesis by measuring solution and solid-state absorption, cyclic voltammetry as well as characterizing the films by grazing incident wide angle X-ray scattering (GIWAXS). In a second step, we repeat the characterization of the three materials in blends with two polymer donors, namely PCDTBT or PBDBT, whose energy levels are well aligned with those of the PI acceptors, and which, additionally, exhibit different degrees of structural order. We show how the initial strong difference between acceptors is partially blurred in blends, but still critical. Finally, we correlate our structural data with OPV devices made with the corresponding six blends. Our data suggest that a good donor acceptor marriage should ensure good energy alignment but also exhibit complementary crystallization tendencies of the two components., The authors acknowledge financial support from the Spanish Ministry of Science and Innovation through the Severo Ochoa” Program for Centers of Excellence in R&D (No. CEX2019-000917-S), and projects PGC2018-095411-B-I00, PID2019-106268GB-C33 and PID2019-110305GB-I00, as well as the European Commission through the Horizon 2020 Marie Sklodowska-Curie ITN Programme, SEPOMO, Grant Number: 722651, and the UCM (INV.GR.00.1819.10759). E.G. specially acknowledges Comunidad de Madrid and Universidad Complutense de Madrid for a post-doctoral contract (CT20/19- CT21/19/PEJD-2018-POST/IND-8661PAI). M.J.A.N. acknowledges URJC for a post-doctoral contract. R.P.O and A.H. also acknowledge support from Junta de Andalucía (projects UMA18-FEDERJA-080). We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

In this work, a series of naphthalimide fused thienopyrazine derivatives was designed, and their synthesis and characterization are reported herein. The interaction of this building block with a donor terthiophene fragment laterally substituted by a series of donor and acceptor constituents was analyzed in depth. This strategy was proven to efficiently modulate both the energy and topology of the frontier molecular orbitals involved in the charge transport mechanism. The interplay between the donor and acceptor strengths of the different units composing the material structure is thus essential to efficiently modulate charge carriers and transport properties and to finely tune the optical and electronic structures of the presented organic semiconductors., This work was financially supported by MINECO (MAT2016-77608-C3-2-P), MICINN (PID2019-106268GB-C33) and the UCM (INV.GR.00.1819.10759). MJAN gratefully acknowledges Universidad Rey Juan Carlos for a predoctoral contract. The university of Málaga acknowledges support from Junta de Andalucia (UMA18-FEDERJA-080) and MICINN (PID2019-110305GB-I00). We also thank CIC NanoGune for technical support in OFET characterization measurements.

Here we have investigated the influence of the molecular length and structure of a series of BTI-based semiconductors on the stabilization of charged states in solution by in situ UV/Vis/NIR spectroelectrochemistry and in the solid state, at the active interface of operational OFET devices, by charge modulation spectroscopy (CMS). Interestingly, we found that charge stabilization in the shortest system of the series (BTI2) is strongly favored via a π-dimer formation which, in addition to higher thin film microstructural ordering, results in a greater electron mobility in organic field effect transistors (OFETs). The experimental results were interpreted using TD-DFT and DFT quantum chemical calculations at different levels of theory.

In this work, a series of nitrogen-doped polycyclic aromatic mono and dicarboximides was designed, and their synthesis is reported by an innovative synthetic procedure that avoids metal-based cross-coupling reactions. A combined theoretical, electrochemical, optical spectroscopy and material characterization study allows the investigation of the interplay of different effects such as (i) the type of solubilizing chain, (ii) the all-acceptor vs. donor–acceptor nature of the novel systems, and (iii) the molecular ordering, on the ability to stabilize multiple charges and on the OTFT device response characteristics. The amphoteric redox behavior of some of the novel systems allow to obtain ambipolar mobilities while the electron mobility values of the three all-acceptor systems can be rationalized in terms of supramolecular aggregation and enhanced film-forming ability. Funding for open access charge: Universidad de Málaga. This work was financially supported by MICINN (PID2019-106268GB-C33) and the UCM (INV.GR.00.1819.10759). MJAN gratefully acknowledges Universidad Rey Juan Carlos for a predoctoral contract. The university of Ma´laga acknowledges support from Junta de Andalucı´a (projects UMA18-FEDERJA080 and P18-FR-4559) and MICINN (PID2019-110305GB-I00). RPO and AH also thank the Research Central Services (SCAI) of the University of Ma´laga and especially the Vibrational Spectroscopy Laboratory.

The first example of an n-type [1]benzothieno[3,2-b][1]benzothiophene (BTBT)-based semiconductor, D-(PhFCO)-BTBT, has been realized via a two-step transition metal-free process without using chromatographic purification. Physicochemical and optoelectronic characterizations of the new semiconductor were performed in detail, and the crystal structure was accessed. The new molecule exhibits a large optical band gap (similar to 2.9 eV) and highly stabilized (Delta E-LUMO = 1.54 eV)/pi-delocalized lowest unoccupied molecular orbital (LUMO) mainly comprising the BTBT pi-core and in-plane carbonyl units. The effect of out-of-plane twisted (64 degrees) pentafluorophenyl groups on LUMO stabilization is found to be minimal. Polycrystalline D(PhFCO)-BTBT thin films prepared by physical vapor deposition exhibited large grains (similar to 2-5 mu m sizes) and "layer-by-layer" stacked edge-on oriented molecules with an in-plane herringbone packing (intermolecular distances similar to 3.25-3.46 angstrom) to favor two-dimensional (2D) source-to-drain (S -> D) charge transport. The corresponding TC/BG-OFET devices demonstrated high electron mobilities of up to similar to 0.6 cm(2)/V.s and I-on/I-off ratios over 10(7)-10(8). These results demonstrate that the large band gap BTBT pi-core is a promising candidate for high-mobility n-type organic semiconductors and, combination of very large intrinsic charge transport capabilities and optical transparency, may open a new perspective for next-generation unconventional (opto)electronics.

New organic semiconductors are essential for developing inexpensive, high-efficiency, solution-processable polymer solar cells (PSCs). PSC photoactive layers are typically fabricated by film-casting a donor polymer and a fullerene acceptor blend, with ensuing solvent evaporation and phase separation creating discrete conduits for photogenerated holes and electrons. Until recently, n-type fullerene acceptors dominated the PSC literature; however, indacenodithienothiophene (IDTT)-based acceptors have recently enabled remarkable PSC performance metrics, for reasons that are not entirely obvious. We report two isomeric IDTT-based acceptors 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-benz-(5, 6)indanone))-5,5,11,11-tetrakis(4-nonylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]di-thiophene (ITN-C9) and 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-benz(6,7)indanone))-5,5,11,11-tetrakis(4-nonylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (ITzN-C9) that shed light on the exceptional IDTT properties vis-à-vis fullerenes. The neat acceptors and blends with fluoropolymer donor poly{[4,8-bis[5-(2- ethylhexyl)-4-fluoro-2-thienyl]benzo[1,2-b:4,5-b′]dithiophene2,6-diyl]-alt-[2,5-thiophenediyl[5,7-bis(2-ethylhexyl)-4,8-dioxo4H,8H-benzo[1,2-c:4,5-c′]dithiophene-1,3-diyl]]} (PBDB-TF) are investigated by optical spectroscopy, cyclic voltammetry, thermogravimetric analysis, differential scanning calorimetry, single-crystal X-ray diffraction, photovoltaic response, space-charge-limited current transport, atomic force microscopy, grazing incidence wide-angle X-ray scattering, and density functional theory-level quantum chemical analysis. The data reveal that ITN-C9 and ITzN-C9 organize such that the lowest unoccupied molecular orbital-rich end groups have intermolecular π−π distances as close as 3.31(1) Å, with electronic coupling integrals as large as 38 meV, and internal reorganization energies as small as 0.133 eV, comparable to or superior to those in fullerenes. ITN-C9 and ITzN-C9 have broad solar-relevant optical absorption, and, when blended with PBDB-TF, afford devices with power conversion efficiencies near 10%. Performance differences between ITN-C9 and ITzN-C9 are understandable in terms of molecular and electronic structure distinctions via the influences on molecular packing and orientation with respect to the electrode.

Development of high-performance unipolar n-type organic semiconductors still remains as a great challenge. In this work, all-acceptor bithiophene imide-based ladder-type small molecules BTIn and semiladder-type homopolymers PBTIn (n = 1–5) were synthesized, and their structure–property correlations were studied in depth. It was found that Pd-catalyzed Stille coupling is superior to Ni-mediated Yamamoto coupling to produce polymers with higher molecular weight and improved polymer quality, thus leading to greatly increased electron mobility (μe). Due to their all-acceptor backbone, these polymers all exhibit unipolar n-type transport in organic thin-film transistors, accompanied by low off-currents (10–10–10–9 A), large on/off current ratios (106), and small threshold voltages (∼15–25 V). The highest μe, up to 3.71 cm2 V–1 s–1, is attained from PBTI1 with the shortest monomer unit. As the monomer size is extended, the μe drops by 2 orders to 0.014 cm2 V–1 s–1 for PBTI5. This monotonic decrease of μe was al...