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[Abstract] Emergent bioelectronic technologies are underpinned by the organic electrochemical transistor (OECT), which employs an electrolyte medium to modulate the conductivity of its organic semiconductor channel. Here we utilize postpolymerization modification (PPM) on a conjugated polymer backbone to directly introduce glycolated or anionic side chains via fluoride displacement. The resulting polymers demonstrated increased volumetric capacitances, with subdued swelling, compared to their parent polymer in p-type enhancement mode OECTs. This increase in capacitance was attributed to their modified side chain configurations enabling cationic charge compensation for thin film electrochemical oxidation, as deduced from electrochemical quartz crystal microbalance measurements. An overall improvement in OECT performance was recorded for the hybrid glycol/ionic polymer compared to the parent, owing to its low swelling and bimodal crystalline orientation as imaged by grazing-incidence wide-angle X-ray scattering, enabling its high charge mobility at 1.02 cm2·V–1·s–1. Compromised device performance was recorded for the fully glycolated derivative compared to the parent, which was linked to its limited face-on stacking, which hindered OECT charge mobility at 0.26 cm2·V–1·s–1, despite its high capacitance. These results highlight the effectiveness of anionic side chain attachment by PPM as a means of increasing the volumetric capacitance of p-type conjugated polymers for OECTs, while retaining solid-state macromolecular properties that facilitate hole transport. Reino Unido. Engineering and Physical Sciences Research Council; EP/T028513/1 República de Corea. Global Research Laboratory program; NRF-2017K1A1A2013153 República de Corea. National Research Foundation of Korea; RF-2021R1A2C101301511 569 República de Corea. National Research Foundation of Korea; 2021R1A2C1013015 República de Corea. National Research Foundation of Korea; 2018M3A7B4070988 República de Corea. National Research Foundation of Korea; 2021R1A4A1022920

[Abstract]: We report the first examples of carborane-containing non-fullerene acceptors (NFAs), and their use in organic photovoltaic (OPV) devices. NFAs employing an A–D–A′–D–A type design centred around a central electron withdrawing carborane unit (A′), using either para, meta, or ortho-carborane isomers are reported. We demonstrate that the nature of the isomer has a major impact on device performance, despite minor differences in optoelectronic and morphological properties, with the use of ortho-carborane resulting in the highest device efficiencies. We further show that end-group fluorination is an efficient strategy to modulate energy levels and improve device performance of such NFAs. Reino Unido. Physics Science Research Council; EP/V048686/1 Reino Unido. Physics Science Research Council; EP/T028513/1 Arabia Saudí. King Abdullah University of Science and Technology; OSR-2019-CRG8-4095

Circularly polarised light will revolutionise emerging technologies, including encrypted light-based communications, quantum computing, bioimaging and multi-channel data processing. In order to make use of these remarkable opportunities, high performance photodetectors that can accurately differentiate between left- and right-handed circularly polarised light are desperately needed. Whilst this potential has resulted in considerable research interest in chiral materials and circularly polarised photodetecting devices, their translation into real-world technologies is limited by non-standardised reporting and testing protocols. This mini-review provides an accessible introduction into the working principles of circularly polarised photodetectors and a comprehensive overview of the performance metrics of state-of-the-art devices. We propose a rigorous device characterisation procedure that will allow for standardised evaluation of novel devices, which we hope will accelerate research and investment in this area.

Bimolecular processes involving exciton spin-state interactions gain attention for their deployment as wavelength-shifting tools. Particularly triplet–triplet annihilation induced photon energy up-conversion (TTA-UC) holds promise to enhance the performance of solar cell and photodetection technologies. Despite the progress noted, a correlation between the solid-state microstructure of photoactuating TTA-UC organic composites and their photophysical properties is missing. This lack of knowledge impedes the effective integration of functional TTA-UC interlayers as ancillary components in operating devices. We here investigate a solution-processed model green-to-blue TTA-UC binary composite. Solid-state films of a 9,10 diphenyl anthracene (DPA) blue-emitting activator blended with a (2,3,7,8,12,13,17,18-octaethyl-porphyrinato) PtII (PtOEP) green-absorbing sensitizer are prepared with a range of compositions and examined by a set of complementary characterization techniques. Grazing incidence X-ray diffractometry (GIXRD) measurements identify three PtOEP composition regions wherein the DPA:PtOEP composite microstructure varies due to changes in the packing motifs of the DPA and PtOEP phases. In Region 1 (≤2 wt%) DPA is semicrystalline and PtOEP is amorphous, in Region 2 (between 2 and 10 wt%) both DPA and PtOEP phases are amorphous, and in Region 3 (≥10 wt%) DPA remains amorphous and PtOEP is semicrystalline. GIXRD further reveals the metastable DPA-β polymorph species as the dominant DPA phase in Region 1. Composition dependent UV-vis and FT-IR measurements identify physical PtOEP dimers, irrespective of the structural order in the PtOEP phase. Time-gated photoluminescence (PL) spectroscopy and scanning electron microscopy imaging confirm the presence of PtOEP aggregates, even after dispersing DPA:PtOEP in amorphous poly(styrene). When arrested in Regions 1 and 2, DPA:PtOEP exhibits delayed PtOEP fluorescence at 580 nm that follows a power-law decay on the ns time scale. The origin of PtOEP delayed fluorescence is unraveled by temperature- and fluence-dependent PL experiments. Triplet PtOEP excitations undergo dispersive diffusion and enable TTA reactions that activate the first singlet-excited (S1) PtOEP state. The effect is reproduced when PtOEP is mixed with a poly(fluorene-2-octyl) (PFO) derivative. Transient absorption measurements on PFO:PtOEP films find that selective PtOEP photoexcitation activates the S1 of PFO within ∼100 fs through an up-converted 3(d, d*) PtII-centered state.

Tuning halide composition in perovskites is a powerful approach demonstrated to enhance the performance of perovskite photovoltaic devices where such compositional modifications drive improvements in open-circuit voltage (Voc) and a reduction in nonradiative voltage losses. Similarly, photodetectors (PDs) operate as light to current conversion devices hence it is relevant to investigate whether performance enhancements can be achieved by similar strategies. Herein, perovskite PDs are fabricated with an inverted photodiode configuration based on a MAPb(I1-xBrx)3 perovskite (MA = methylammonium) active layer over the x = 0–0.25 composition range. Interestingly, it has been found that increasing the Br content up to 0.15 (15%) leads to a significant reduction in dark current (Jd), with values as low as 1.3 × 10−9 A cm−2 being achieved alongside a specific detectivity of 8.7 × 1012 Jones. Significantly, it has been observed an exponential relationship between the Jd of devices and their Voc over the 0–15% Br range. The superior performances of the 15% Br-containing devices are attributed to the reduction of trap states, a better charge extraction of photogenerated carriers, and an improvement in photoactive layer morphology and crystallinity.

Organic materials combining high electron affinity with strong absorption in the visible spectrum are of interest for photodetector applications. In this study, we report two such molecular semiconductors, based upon an acceptor-donor-acceptor (A-D-A) approach. Coupling of an acceptor end group, 2,1,3-benzothiadiazole-4,5,6-tricarbonitrile (TCNBT), with a donor cyclopentadithiophene core affords materials with a band gap of 1.5 eV and low-lying LUMO levels around -4.2 eV. Both materials were readily synthesized by a one-pot nucleophilic displacement of a fluorinated precursor by cyanide. The two acceptors only differ in the nature of the solubilizing alkyl chain, which is either branched 2-ethyl hexyl (EH-TCNBT) or linear octyl (O-TCNBT). Both acceptors were blended with polymer donor PTQ10 as an active layer in OPDs. Significant device differences were observed depending on the alkyl chain, with the branched acceptor giving the optimum performance. Both acceptors exhibited very low dark current densities, with values up to 10

Summary Stable and efficient perovskite/silicon tandem solar cells require defect passivation and suppression of light-induced phase segregation of the wide-band-gap perovskite. Here, we report how molecules containing both electron-rich and electron-poor moieties, such as phenformin hydrochloride (PhenHCl), can satisfy both requirements, independent of the perovskite’s surface chemical composition and its grain boundaries and interfaces. PhenHCl-passivated wide-band-gap (∼1.68 eV) perovskite p-i-n single-junction solar cells deliver an open-circuit voltage (VOC) ∼100 mV higher than control devices, resulting in power conversion efficiencies (PCEs) up to 20.5%. These devices do not show any VOC losses after more than 3,000 h of thermal stress at 85°C in a nitrogen ambient. Moreover, PhenHCl passivation improves the PCE of textured perovskite/silicon tandem solar cells from 25.4% to 27.4%. Our findings provide critical insights for improved passivation of metal halide perovskite surfaces and the fabrication of highly efficient and stable perovskite-based single-junction and tandem solar cells.

Owing to their unique porosity and large surface area, porous organic polymers (POPs) have shown their presence in numerous novel applications. The tunability and functionality of both the pores and backbone of the material enable its suitability in photovoltaic devices. The porosity induced host-guest configurations as well as periodic donor-acceptor structures benefit the charge separation and charge transfer in photophysical processes. The role of POPS in other critical device components, such as hole transporting layers and electrodes, has also been demonstrated. Herein, this review will primarily focus on the recent progress made in applying POPs for solar cell device performance enhancement, covering organic solar cells, perovskite solar cells, and dye-sensitized solar cells. Based on the efforts in recent years in unraveling POP's photophysical process and its relevance with device performances, an in-depth analysis will be provided to address the gradual shift of attention from an entirely POP-based active layer to other device functional components. Combining the insights from device physics, material synthesis, and microfabrication, we aim to unfold the fundamental limitations and challenges of POPs and shed light on future research directions.

Donor-acceptor (D-A) polymers are promising materials for organic electrochemical transistors (OECTs), as they minimize detrimental faradaic side-reactions during OECT operation, yet their steady-state OECT performance still lags far behind their all-donor counterparts. Here, we report three D-A polymers based on the diketopyrrolopyrrole unit that afford OECT performances similar to those of all-donor polymers, hence representing a significant improvement to the previously developed D-A copolymers. In addition to improved OECT performance, DFT simulations of the polymers and their respective hole polarons also revealed a positive correlation between hole polaron delocalization and steady-state OECT performance, providing new insights into the design of OECT materials. More importantly, we demonstrate how polaron delocalization can be tuned directly at the molecular level by selection of the building blocks comprising the polymers' conjugated backbone, thus paving the way for the development of even higher performing OECT polymers.

Solution-processed organic photodetectors (OPDs) sensitive to infrared (IR) light have the potential to be used in various technologies from health monitoring to communication. These detectors require low bandgap materials absorbing photons beyond 750 nm with high responsivity. In this work, an ultra-low bandgap non-fullerene acceptor (NFA) that absorbs light until 1020 nm is developed. Used in a bulk heterojunction (BHJ)-based device, the photodetector has a maximum responsivity of 0.50 A W−1 at 890 nm without bias voltage comparable with silicon-based detectors. Due to high and balanced mobilities of 10−4 cm2 V−1 s−1, the device has a fast speed of response to IR (i.e. rise and decay time less than 4 μs) and minor damping of 1 dB in the IR communication range (38–50 kHz). The organic photodetector transcripts with accuracy the message emitted around 910 nm from a commercial remote control, thus demonstrating the potential of organic electronics for infrared communication.

Three n-type fused lactam semiconducting polymers were synthesized for thermoelectric and transistor applications via a cheap, highly atom-efficient, and nontoxic transition-metal free aldol polycondensation. Energy level analysis of the three polymers demonstrated that reducing the central acene core size from two anthracenes (A-A), to mixed naphthalene-anthracene (A-N), and two naphthalene cores (N-N) resulted in progressively larger electron affinities, thereby suggesting an increasingly more favorable and efficient solution doping process when employing 4-(2,3-dihydro-1,3-dimethyl-1H-benzimidazol-2-yl)-N,N-dimethylbenzenamine (N-DMBI) as the dopant. Meanwhile, organic field effect transistor (OFET) mobility data showed the N-N and A-N polymers to feature the highest charge carrier mobilities, further highlighting the benefits of aryl core contraction to the electronic performance of the materials. Ultimately, the combination of these two factors resulted in N-N, A-N, and A-A to display power factors (PFs) of 3.2 μW m-1 K-2, 1.6 μW m-1 K-2, and 0.3 μW m-1 K-2, respectively, when doped with N-DMBI, whereby the PFs recorded for N-N and A-N are among the highest reported in the literature for n-type polymers. Importantly, the results reported in this study highlight that modulating the size of the central acene ring is a highly effective molecular design strategy to optimize the thermoelectric performance of conjugated polymers, thus also providing new insights into the molecular design guidelines for the next generation of high-performance n-type materials for thermoelectric applications.

A series of fully fused n-type mixed conduction lactam polymers p(g(7)NC(n)N), systematically increasing the alkyl side chain content, are synthesized via an inexpensive, nontoxic, precious-metal-free aldol polycondensation. Employing these polymers as channel materials in organic electrochemical transistors (OECTs) affords state-of-the-art n-type performance with p(g(7)NC(10)N) recording an OECT electron mobility of 1.20 x 10(-2) cm(2) V-1 s(-1) and a mu C* figure of merit of 1.83 F cm(-1) V-1 s(-1). In parallel to high OECT performance, upon solution doping with (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI), the highest thermoelectric performance is observed for p(g(7)NC(4)N), with a maximum electrical conductivity of 7.67 S cm(-1) and a power factor of 10.4 mu Wm(-1) K-2. These results are among the highest reported for n-type polymers. Importantly, while this series of fused polylactam organic mixed ionic-electronic conductors (OMIECs) highlights that synthetic molecular design strategies to bolster OECT performance can be translated to also achieve high organic thermoelectric (OTE) performance, a nuanced synthetic approach must be used to optimize performance. Herein, we outline the performance metrics and provide new insights into the molecular design guidelines for the next generation of high-performance n-type materials for mixed conduction applications, presenting for the first time the results of a single polymer series within both OECT and OTE applications. Funding Agencies|KAUSTKing Abdullah University of Science & Technology; Office of Sponsored Research (OSR) award [OSR-2018-CRG/CCF-3079, OSR-2019CRG8-4086, OSR-2018-CRG7-3749]; ERC Synergy Grant SC2 [610115]; European UnionEuropean Commission [952911, 862474, 945380]; EPSRCUK Research & Innovation (UKRI)Engineering & Physical Sciences Research Council (EPSRC) [EP/T026219/1]; NSFNational Science Foundation (NSF) [DMR-1751308]; National Science FoundationNational Science Foundation (NSF) [NSF DMR-1751308]; DOE Office of ScienceUnited States Department of Energy (DOE) [DE-AC02-06CH11357]; SHyNE Resource [NSF ECCS-1542205]; IIN; Northwesterns MRSEC program [NSF DMR-1720139]; Swedish Research CouncilSwedish Research CouncilEuropean Commission [202003243]; European Commission through the Marie Sklodowska-Curie project HORATES [GA-955837]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant) [SFO-Mat-LiU 2009-00971]

Recent efforts in the field of organic photodetectors (OPD) have been focused on extending broadband detection into the near-infrared (NIR) region. Here, two blends of an ultralow bandgap push–pull polymer TQ-T combined with state-of-the-art non-fullerene acceptors, IEICO-4F and Y6, are compared to obtain OPDs for sensing in the NIR beyond 1100 nm, which is the cut off for benchmark Si photodiodes. It is observed that the TQ-T:IEICO-4F device has a superior IR responsivity (0.03 AW-1 at 1200 nm and −2 V bias) and can detect infrared light up to 1800 nm, while the TQ-T:Y6 blend shows a lower responsivity of 0.01 AW-1. Device physics analyses are tied with spectroscopic and morphological studies to link the superior performance of TQ-T:IEICO-4F OPD to its faster charge separation as well as more favorable donor–acceptor domains mixing. In the polymer blend with Y6, the formation of large agglomerates that exceed the exciton diffusion length, which leads to high charge recombination, is observed. An application of these devices as biometric sensors for real-time heart rate monitoring via photoplethysmography, utilizing infrared light, is demonstrated.

Recent advancements in light-responsive materials enabled the development of devices to artificially activate tissue with light, and show great potential for use in different types of therapy. Photo-stimulation based on organic semiconductors has recently attracted interest due to their unique set of properties such as biocompatibility, better mechanical match with human tissue, and strong absorption of light in the visible spectrum. Here we show the development of solution processed organic heterojunctions that are able to control the activity of primary neurons in vitro with light. The p-type polymer semiconductor PDCBT and the n-type polymer semiconductor ITIC (also known as non-fullerene acceptor) are simply spin coated on glass substrates forming a bilayer p-n junction with high photo-sensitivity in aqueous electrolytes. Photo-electrochemical measurements reveal that high photo-voltage and photo-current is produced, as a result of a charge transfer between the polymers and oxygen in the electrolyte. The biocompatibility of the proposed materials is addressed with live/dead assays on both primary mouse cortical neurons and human cell lines that are cultured on their surface. We have found that light of low intensity (i.e. 40 mW/cm2) is absorbed, and converted into a cue that triggers action potential on primary cortical neurons directly cultured on glass/PDCBT/ITIC interfaces as proven by patch clamp measurements. The activation of neurons is most likely due to photochemical reactions at the polymer/electrolyte interface that result in hydrogen peroxide, which might lead to modulation of specific ion channels on neurons membrane. Photo-thermal effects are excluded with controlled patch clamp measurements on neurons cultured on plain glass and on photoresist thin films. The profound advantages of low intensity light stimulation, simplified fabrication, and wireless operation pave the way for the integration of these interfaces in multiplex bioelectronic devices for the development of novel light therapy concepts and powerful neuroscience research tools.

Ternary organic solar cells based on polymer donor and nonfullerene acceptors (NFAs) are delivering high power conversion efficiencies (PCE). Now, further improvement needs to be directed to enhanc...

We acknowledge the use of KAUST Core Lab and KAUST Solar Center facilities. This work was supported by KAUST and the Office of Sponsored Research (OSR) under award no. OSR-2017-CRG-3380. F.G. is a Wallenberg Academy Fellow.

We demonstrate the synthesis of three π-conjugated terpolymers based on the nonconventional molecular design strategy D1–D2–D1–A comprising two different multi-fused ladder-type arene electron donating moieties [(4,4′-bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)-2,6-diyl (DTS) as D1 and thienyl-substituted benzo[1,2-b:4,5-b′]dithiophene (BDT) derivatives as D2] and an electron withdrawing unit [5,6-difluoro-2,1,3-benzothiadiazole (DFBT) as A]. The implementation of these materials as electron donors is explored in high performance near infrared non-fullerene acceptor (NFA) organic solar cells utilizing the benchmark low bandgap NFA IEICO-4F. The triple bulk heterojunction blend systems provide the basis for a detailed structure–property–performance relationship in terms of BDT's thienyl substitution (alkyl, alkylthio and fluoro) by investigating the correlations between the molecular energy level alignments, performance, and device physics of OSCs. The alkylthienyl-BDT based π-conjugated terpolymer [P(DTS-BDT-DFBT)] exhibits the best photovoltaic performance delivering a power conversion efficiency of 10% with a high short circuit current density of 22.7 mA cm−2. The combination of optoelectronic measurements and morphological analyses revealed the suppression of field dependent charge recombination in P(DTS-BDT-DFBT):IEICO-4F as compared to alkylthiothienyl-BDT [P(DTS-BDTS-DFBT):IEICO-4F] and fluoro-substituted thienyl-BDT [P(DTS-BDTF-DFBT):IEICO-4F] based OSC devices.

Optoelectronic devices typically require low-resistance ohmic contacts between the optical active layers and metal electrodes. Failure to make such a contact often results in a Schottky barrier which inhibits charge extraction and, in turn, reduces device performance. Here, we introduce a universal solution processable metal-oxide/organic interfacial bilayer which forms a near-perfect ohmic contact between both organic and inorganic semiconductors and metals. This bilayer comprises a Nb-doped TiO2 metal oxide with enhanced electron mobility and reduced trap density compared to pristine TiO2, in combination with a metal-chelating organic molecule to make an intimate electrical contact with silver metallic electrodes. Using this universal interfacial bilayer, we demonstrate substantial efficiency improvements in organic solar cells (from 9.3% to 12.6% PCE), light emitting diodes (from 0.6 to 2.2 cd W−1) and transistors (from 19.7 to 13.9 V threshold voltage). In particular, a boost in efficiency for perovskite solar cells (from 18.7% up to 20.7% PCE) with up to 83% fill factor is achieved with no-operational lifetime loss for at least 1000 hours under continuous, full-spectrum illumination.

Antisolvent-assisted spin coating has been widely used for fabricating metal halide perovskite films with smooth and compact morphology. However, localized nanoscale inhomogeneities exist in these films owing to rapid crystallization, undermining their overall optoelectronic performance. Here, we show that by relaxing the requirement for film smoothness, outstanding film quality can be obtained simply through a post-annealing grain growth process without passivation agents. The morphological changes, driven by a vaporized methylammonium chloride (MACl)-dimethylformamide (DMF) solution, lead to comprehensive defect elimination. Our nanoscale characterization visualizes the local defective clusters in the as-deposited film and their elimination following treatment, which couples with the observation of emissive grain boundaries and excellent inter- and intragrain optoelectronic uniformity in the polycrystalline film. Overcoming these performance-limiting inhomogeneities results in the enhancement of the photoresponse to low-light (

Recent advances in the development of organic photovoltaic (OPV) materials has led to significant improvements in device performance; now closing in on the 20% efficiency threshold. Despite these improvements in performance, the commercial viability of organic photovoltaic products remains elusive. In this perspective, the current limitations of high performing blends are uncovered, particularly focusing on the industrial upscaling considerations of these materials, such as synthetic scalability, active layer processing, and device stability. Moreover, a simplified metric, namely, the scalability factor (SF), is introduced to evaluate the scale-up potential of specific OPV materials and blends thereof. Of the most popular molecular design strategies investigated in recent times, it is found that the use of Y-series nonfullerene acceptors (NFAs) and synthetically simple materials, such as PTQ-10 and ternary blends, are most effective at maximizing the efficiency without negatively impacting the SF. Furthermore, the improvements that are needed, in terms of device processability and stability, are considered for industrial scale-up and final product application. Finally, an outlook of organic photovoltaics is provided both from a perspective of important research avenues and applications that can be exploited.

We report on three novel n-type conjugated polymer semiconductors incorporating carborane in the polymer backbone and demonstrate their applicability in optoelectronic devices. Comparing the optoelectronic properties of para-, meta-, and ortho-carborane isomers revealed similar energetic characteristics between the different polymers, with the carborane unit acting as a “conjugation breaker”, confining electron delocalisation to the conjugated moieties. The fabrication of all-polymer organic photovoltaic (OPV) devices and thin-film transistors (TFTs) revealed some differences in device performance between the polymers, with the meta-carborane based polymer exhibiting superior performance in both OPV and TFT devices.

To date, many of the high-performance conjugated polymers employed as OECT channel materials make use of ethylene glycol (EG) chains to confer the materials with mixed ionic-electronic conduction properties, with limited emphasis placed on alternative hydrophilic moieties. While a degree of hydrophilicity is required to facilitate some ionic conduction in hydrated channels, an excess results in excessive swelling, with potentially detrimental effects on charge transport. This is therefore a subtle balance that must be optimised to maximise electrical performance. Herein a series of polymers based on a bithiophene-thienothiophene conjugated backbone was synthesised and the conventional EG chains substituted by their propylene and butylene counterparts. Specifically, the use of propylene and butylene chains was found to afford polymers with a more hydrophobic character, thereby reducing excessive water uptake during OECT operation and in turn significantly boosting the polymers' electronic charge carrier mobility. Despite the polymers' lower water uptake, the newly developed oligoether chains retained sufficiently high degrees of hydrophilicity to enable bulk volumetric doping, ultimately resulting in the development of polymers with superior OECT performance.

Summary Defect passivation and surface modification of hybrid perovskite films are essential to achieving high power conversion efficiency (PCE) and stable perovskite photovoltaics. Here, we demonstrate a facile strategy that combines high PCE with high stability in CH3NH3PbI3 (MAPbI3) solar cells. The strategy utilizes inorganic perovskite quantum dots (QDs) to distribute elemental dopants uniformly across the MAPbI3 film and attach ligands to the film’s surface. Compared with pristine MAPbI3 films, MAPbI3 films processed with QDs show a reduction in tail states, smaller trap-state density, and an increase in carrier recombination lifetime. This strategy results in reduced voltage losses and an improvement in PCE from 18.3% to 21.5%, which is among the highest efficiencies for MAPbI3 devices. Ligands introduced with the aid of the QDs render the perovskite film’s surface hydrophobic—inhibiting moisture penetration. The devices maintain 80% of their initial PCE under 1-sun continuous illumination for 500 h and show improved thermal stability.

Ternary organic solar cells (TSCs) contain a single three-component photoactive layer with a wide absorption window, which is obtained without the need for multiple stacks. Subsequently, TSCs have attracted great interest in the photovoltaics field. Through careful selection of the three (or more) active components that form the photoactive layer, all photovoltaic parameters can be simultaneously enhanced within a TSC — a strategy that has resulted in record efficiencies for single-junction solar cells. In this Review, we outline key developments in TSCs, with a focus on the central role of the third component in achieving record efficiencies. We analyse the effects of the third component on the nanomorphology of the bulk heterojunction and the photovoltaic parameters of TSCs. Moreover, we discuss the charge-transfer and/or energy-transfer mechanisms and nanomorphology models that govern the operation of TSCs. We consider both polymer and small-molecule donors as well as fullerenes and recently developed non-fullerene acceptors. In addition, we summarize the recent success of TSCs in mitigating the stability issues of binary solar cells. Finally, we provide a perspective on the advantages of ternary blends and suggest design strategies for highly efficient and stable devices for commercial photovoltaics. Adding a third component into a binary blend is a promising strategy for simultaneously improving all photovoltaic parameters in organic solar cells. In this Review, we discuss the role of the third component in influencing the energetics, charge-carrier recombination and stability in ternary solar cells.

Summary Herein, we report ternary organic solar cells with a power conversion efficiency (PCE) of 14.0%. By incorporating 10 wt % of BIT-4F-T in the PTB7-Th:IEICO-4F blend, we obtain an enhancement of all photovoltaic parameters compared to the binary devices, leading to a 15% performance improvement in ternary blend. The high photocurrent in 10% BIT-4F-T blend results from a complementary absorption profile of donor components and a hole transfer from BIT-4F-T to PTB7-Th. Morphological and device characterizations reveal that the addition of 10% BIT-4F-T acts not only as a sensitizer but also as a solid processing aid, which is beneficial for charge generation and transport. The effect of the third component is observed in different non-fullerene and fullerene OSCs. Our study demonstrates that careful selection of a third component, where dual sensitizing and processing-aid effects are observed, can be a design strategy to achieve a concomitant improvement in all photovoltaic parameters.

A narrow-band-gap molecular acceptor, IPIC-4Cl, featuring an indacenobis(dithieno[3,2-b:2′,3′-d]pyrrol) (INP) core with 2-butyl-1-octyl side chains and chlorinated (dicyanomethylidene)-indan-1-one (IC) as electron-accepting end group, has been rationally designed as nonfullerene acceptors (NFAs) for organic solar cells (OSCs). The impact of chlorination on the acceptor unit is revealed by a comparison study with two counterpart NFAs bearing a fluorinated or nonhalogenated IC unit. The synergetic photophysical and morphological analyses reveal that PBDB-T:IPIC-4Cl blend possesses efficient exciton dissociation and charge collection integrated with higher crystallinity and optimized phase separation. Consequently, the OSCs constructed by PBDB-T:IPIC-4Cl obtain a champion power conversion efficiency (PCE) of 13.4% with an extremely low energy loss of 0.51 eV. More encouragingly, we achieve a higher photovoltaic performance of 14.3% for ternary solar cells by combining an optimal amount of PC71BM with PBDB-T:...

Recent advances demonstrate the efficacy of ternary strategy in organic solar cells. Such excitement is achieved by synergistic improvement in both charge dynamics and energetics. The third component serves as a bridging unit to systematically optimize the charge migration, exciton lifetime, recombination, and nanomorphology. Primarily focusing on the tactics for addressing energy transfer, charge transfer, and voltage losses, specific relationship between kinetics and energetics evolution has been thoroughly analyzed upon addition of the third component. We propose that the future design should be beyond simply complementing absorption, but rather focus on how the guest molecular could specifically address the charge and energy profile. With fine control of morphology, the maximum potential of ternary blends can be realized toward highly efficient organic solar cells.

The development of all-printed, flexible solar cells of high efficiency and ultra-low weight will offer advancements for new market entrants. Herein, we report the design and fabrication of all-printed in ambient air, super-flexible perovskite solar cells with approaching 20% power conversion efficiency and extremely low weight of 5.1 g m-2 leading to an unprecedented power-to-weight ratio of 38,470 W Kg-1. This performance advance was achieved through the design of a highly transparent and conducting nanopaper used as a free-standing bottom electrode (FSBE). The FSBE consisted of cellulose nanocrystals grafted with semi-metallic super-reduced polyoxometalate clusters that enabled high conductivities up to 18 S cm-1 combined with transparency >96%. It also acted as a conformal barrier preventing performance loss upon heating at 95 oC under continuous illumination in inert environment; and strong resistance to decomposition when immersed in a mild citric acid water solution for 100 days, which we further exploit to demonstrate full device recyclability. The inherent flexibility of cellulose nanocrystals enabled remarkable flexibility of these cells under 2,000 repeated bending and folding cycles and mechanical strength upon extensive strain up to 20%. Notably, the nanopaper remained unaffected for strains up to 60%. These findings open the door for efficient and lightweight solar cells with a low environmental impact.

A critical bottleneck for improving the performance of organic solar cells (OSC) is minimising non-radiative losses in the interfacial charge-transfer (CT) state via the formation of hybrid energetic states. This requires small energetic offsets often detrimental for high external quantum efficiency (EQE). Here, we obtain OSC with both non-radiative voltage losses (0.24 V) and photocurrent losses (EQE > 80%) simultaneously minimised. The interfacial CT states separate into free carriers with ≈40-ps time constant. We combine device and spectroscopic data to model the thermodynamics of charge separation and extraction, revealing that the relatively high performance of the devices arises from an optimal adjustment of the CT state energy, which determines how the available overall driving force is efficiently used to maximize both exciton splitting and charge separation. The model proposed is universal for donor:acceptor (D:A) with low driving forces and predicts which D:A will benefit from a morphology optimization for highly efficient OSC., Understanding the mechanism of non-radiative losses in organic photovoltaics is crucial to improve the performance further. Here, the authors use combined device and spectroscopic data to reveal universal model to maximise exciton splitting and charge separation by adjusting the energy of charge transfer state.

It is well established that for organic photodetectors (OPDs) to compete with their inorganic counterparts, low dark currents at reverse bias must be achieved. Here, two rhodanine-terminated nonfullerene acceptors O-FBR and O-IDTBR are shown to deliver low dark currents at -2 V of 0.17 and 0.84 nA cm-2, respectively, when combined with the synthetically scalable polymer PTQ10 in OPD. These low dark currents contribute to the excellent sensitivity to low light of the detectors, reaching values of 0.57 μW cm-2 for PTQ10:O-FBR-based OPD and 2.12 μW cm-2 for PTQ10:O-IDTBR-based OPD. In both cases, this sensitivity exceeds that of a commercially available silicon photodiode. The responsivity of the PTQ10:O-FBR-based OPD of 0.34 AW-1 under a reverse bias of -2 V also exceeds that of a silicon photodiode. Meanwhile, the responsivity of the PTQ10:O-IDTBR of 0.03 AW-1 is limited by the energetic offset of the blend. The OPDs deliver high specific detectivities of 9.6 × 1012 Jones and 3.3 × 1011 Jones for O-FBR- and O-IDTBR-based blends, respectively. Both active layers are blade-coated in air, making them suitable for high-throughput methods. Finally, all three of the materials can be synthesized at low cost and on a large scale, making these blends good candidates for commercial OPD applications.

A series of glycolated polythiophenes for use in organic electrochemical transistors (OECTs) is designed and synthesized, differing in the distribution of their ethylene glycol chains that are tethered to the conjugated backbone. While side chain redistribution does not have a significant impact on the optoelectronic properties of the polymers, this molecular engineering strategy strongly impacts the water uptake achieved in the polymers. By careful optimization of the water uptake in the polymer films, OECTs with unprecedented steady-state performances in terms of [mu C*] and current retentions up to 98% over 700 electrochemical switching cycles are developed. Funding Agencies|KAUSTKing Abdullah University of Science & Technology; King Abdullah University of Science and Technology Office of Sponsored Research (OSR) [OSR-2018-CARF/CCF-3079, OSR-2015-CRG4-2572, OSR-4106 CPF2019]; EC FP7 Project SC2 [610115]; EC H2020 [643791]; EPSRCEngineering & Physical Sciences Research Council (EPSRC) [EP/G037515/1, EP/M005143/1, EP/L016702/1]; Knut and Alice Wallenberg FoundationKnut & Alice Wallenberg Foundation; Wallenberg Wood Science Center [KAW 2018.0452]; Swedish Government Strategic Research Area in Materials Science on Advanced Functional Materials at Linkoping University [2009-00971]; TomKat Center for Sustainable Energy at Stanford University

Elucidating the complex materials distribution in the active layers of ternary organicsolar cells is one of the greatest challenges in the eld of orga nic photov oltaics.Knowledge of the nanomorphology is key to understanding photophysical processes(e.g., charge separation, adjustment of the recombination mechanism, and suppres-sion of the radiationless and energetic losses) and thus improving the device perfor-mance. Herein, for the rst time, the successful discrimination and spatial mappingof the active layer components of a ternary organic solar cell are demonstrated usinganalytical transmission electron microscopy. The material distribution of all threeorganiccomponentsissuccessfullyvisualized by multimodal imaging using com-plementary electron energy loss signals. A complete picture of the morphologicalaspects can be gained by studying the lateral and cross-sectional morphology as wellas the morphology evolution as a function of the mixing ratio of the polymers. Finally,a correlation between the morphology, photophysical processes, and device perfor-mance of the ternary and t he reference binary syst em is achieved, explain ing thedifferences of the powe r conversion efciency between the two systems.

Correction for ‘Best practices in the measurement of circularly polarised photodetectors’ by Matthew D. Ward et al., J. Mater. Chem. C, 2022, 10, 10452–10463, https://doi.org/10.1039/D2TC01224C.