Porous organic polymers are materials with covalently bonded (hydro)thermally stable backbones exhibiting high and accessible surface areas, and properties which are intriguing in the field of (opto)electronics. Especially in organic photovoltaics (OPVs), the electron rich backbone of this class of materials provides exceptional light absorption properties for improved charge formation/separation. Particularly for devices operating via bulk heterojunctions, the rigid open voids along the porous skeleton are rather interesting for improved phase separation and act as an ideal host to the prospective acceptors. Furthermore, their high dimensional geometry allows them to transport electrons/holes independent of orientation issues. However, the non-soluble nature of this class of materials limits their processability for forming uniform films, which is essential for device fabrication. In this review, a brief overview on the reported OPV devices fabricated by applying porous organic polymers in the active layer with the corresponding methods used for film formation will be presented, which will be followed by a discussion regarding possible improvements on the film formation methods and suggestions upon enhancement of the structural/electronic feasibility of the porous backbone.

The demand for further optimization of the photovoltaic efficiency has stimulated an intensive research effort both for new low-band-gap polymeric materials as electron donors and for new efficient electron-accepting materials. As regards the latter, less attention has been observed on the optimization of the electron acceptor material compared to the extensive studies on the electron donor polymer in organic photovoltaic (OPV) cells. The majority of the acceptor materials used so far in solar cells are organic (carbon based) materials, however other traditional acceptor materials include inorganic semiconductors, such as cadmium selenide (CdSe) nanocrystals, titanium oxide (TiO₂) and zinc oxide (ZnO) nanoparticles. From the implemented organic materials high power conversion efficiencies PCEs (>9.0%) are observed in OPVs utilizing fullerene derivatives and especially [6,6]-phenyl-C₆₁ butyric acid methyl ester (PC₆₀BM) as the acceptor. Recently, very promising efficiencies of ∼5.0% have been also obtained by Polyera corporation utilizing soluble conjugated polymers as both the donor and the acceptor components. It is therefore expected that through improved materials design for enhancing the electron mobility, better tuning of the energy levels and absorption profile of organic materials, significant improvements in the device performance can still be expected. In this work, the current trends on the most promising solution processable n-type organic materials (fullerene derivatives, small molecules and conjugated polymers) will be presented in detail, emphasizing on the correlation between structure/optoelectronic properties/morphology characterization and device performances.

We take advantage of a recent breakthrough in the synthesis of α,β-unfunctionalised 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) moieties, which we symmetrically conjugate with oligothienyls in an unexpectedly stable form, and produce a “metal-free” A-D-A (acceptor-donor-acceptor) oligomer emitting in the near-infrared (NIR) thanks to delocalisation of the BODIPY low-lying lowest unoccupied molecular orbital (LUMO) over the oligothienyl moieties, as confirmed by density functional theory (DFT). We are able to retain a PL efficiency of 20% in the solid state (vs. 30% in dilute solutions) by incorporating such a dye in a wider gap polyfluorene matrix and demonstrate organic light-emitting diodes (OLEDs) emitting at 720 nm. We achieve external quantum efficiencies (EQEs) up to 1.1%, the highest value achieved so far by a “metal-free” NIR-OLED not intentionally benefitting from triplet-triplet annihilation. Our work demonstrates for the first time the promise of A-D-A type dyes for NIR OLEDs applications thereby paving the way for further optimisation.

Blue organic light-emitting diodes require high triplet interlayer materials, which induce large energetic barriers at the interfaces resulting in high device voltages and reduced efficiencies. Here, we alleviate this issue by designing a low triplet energy hole transporting interlayer with high mobility, combined with an interface exciplex that confines excitons at the emissive layer/electron transporting material interface. As a result, blue thermally activated delay fluorescent organic light-emitting diodes with a below-bandgap turn-on voltage of 2.5 V and an external quantum efficiency (EQE) of 41.2% were successfully fabricated. These devices also showed suppressed efficiency roll-off maintaining an EQE of 34.8% at 1000 cd m⁻². Our approach paves the way for further progress through exploring alternative device engineering approaches instead of only focusing on the demanding synthesis of organic compounds with complex structures.