Publications
125 results found
Furlan F, Moreno-Naranjo JM, Gasparini N, et al., 2024, Chiral materials and mechanisms for circularly polarized light-emitting diodes, Nature Photonics, ISSN: 1749-4885
Circularly polarized (CP) light-emitting diodes (LEDs) hold great potential for next-generation technologies, from efficient photonic to room-temperature quantum devices. Chiral materials enable the generation of CP electroluminescence in LEDs through several different mechanisms, depending on the choice of material and device architecture. Here we summarize the mechanisms that give rise to CP electroluminescence in state-of-the-art materials, including organic small molecules, polymers, inorganic complexes and hybrid halide perovskites. We explore how the device architecture can be used to control the chiroptical properties and device performance, and suggest improvements to maximize the efficiency and dissymmetry factor of future CP LEDs.
Sharma A, Gasparini N, Markina A, et al., 2024, Semitransparent Organic Photovoltaics Utilizing Intrinsic Charge Generation in Non-Fullerene Acceptors, Advanced Materials, Vol: 36, ISSN: 0935-9648
In organic semiconductors, a donor/acceptor heterojunction is typically required for efficient dissociation of excitons. Using transient absorption spectroscopy to study the dynamics of excited states in non-fullerene acceptors (NFAs), it is shown that NFAs can generate charges without a donor/acceptor interface. This is due to the fact that dielectric solvation provides a driving force sufficient to dissociate the excited state and form the charge-transfer (CT) state. The CT state is further dissociated into free charges at interfaces between polycrystalline regions in neat NFAs. For IEICO-4F, incorporating just 9 wt% donor polymer PTB7-Th in neat films greatly boosts charge generation, enhancing efficient exciton separation into free charges. This property is utilized to fabricate donor-dilute organic photovoltaics (OPV) delivering a power conversion efficiency of 8.3% in the case of opaque devices with a metal top-electrode and an active layer average visible transmittance (AVT) of 75%. It is shown that the intrinsic charge generation in low-bandgap NFAs contributes to the overall photocurrent generation. IEICO-4F-based OPVs with limited PTB7-Th content have high thermal resilience demonstrating little drop in performance over 700 h. PTB7-Th:IEICO-4F semitransparent OPVs are leveraged to fabricate an 8-series connected semitransparent module, demonstrating light-utilization efficiency of 2.2% alongside an AVT of 63%.
Gedeon C, Del Rio N, Furlan F, et al., 2024, Rational design of new conjugated polymers with main chain chirality for efficient optoelectronic devices: carbo[6]helicene and indacenodithiophene copolymers as model compounds, Advanced Materials, ISSN: 0935-9648
The unique properties of conjugated polymers (CPs) in various optoelectronic applications are mainly attributed to their different self-assembly processes and superstructures. Various methods are utilized to tune and control CP structure and properties with less attention paid to the use of chirality. CPs with main chain chirality are rare and their microscopic and macroscopic properties are still unknown. In this work, the first experimental results are provided along these lines by synthesizing a series of racemic and enantiopure CPs containing statistical and alternating carbo[6]helicene and indacenodithiophene moieties and evaluating their microscopic (optical, energy levels) and macroscopic properties (hole mobilities, photovoltaic performance). It is demonstrated that a small statistical insertion of either the racemic or enantiopure helicene into the polymer backbone finely tunes the microscopic and macroscopic properties as a function of the statistical content. The microscopic properties of the enantiopure versus the racemic polymers with the same helicene loading remain similar. On the contrary, the macroscopic properties, and more interestingly those between the two enantiomeric forms, are altered as a function of the statistical content. Once incorporated into a solar cell device, these chiral CPs display better performance in their enantiopure versus racemic forms.
Hu X, Qiao Z, Nodari D, et al., 2024, Remarkable isomer effect on the performance of fully non-fused non-fullerene acceptors in near-infrared organic photodetectors, Advanced Optical Materials, Vol: 12, ISSN: 2195-1071
Two fully non-fused small-molecule acceptors BTIC-1 and BTIC-2 are reported for application in near-infrared organic photodetectors (NIR OPDs). Both acceptors contain the same conjugated backbone but differing sidechain regiochemistry, affording significant differences in their optical properties. The head-to-head arrangement of BTIC-2 results in a reduction of optical band gap of 0.17 eV compared to BTIC-1, which contains a head-to-tail arrangement, with absorption spanning the visible and near-IR regions up to 900 nm. These differences are rationalized on the basis of non-covalent intramolecular interactions facilitating a more co-planar conformation for BTIC-2. OPDs based on PM6:BTIC-2 deliver a low dark current density of 2.4 × 10−7 A cm−2, leading to a superior specific detectivity of 1.7 × 1011 Jones at 828 nm at -2 V. The optimized device exhibits an ultrafast photo response of 2.6 µs and a high -3 dB cut-off frequency of 130 kHz. This work demonstrates that fully non-fused small-molecule acceptors offer competitive device performance for NIR OPDs compared to fused-ring electron acceptors, but with reduced synthetic complexity. Furthermore, the study presents an efficient strategy to enhance device performance by varying conformational locks.
Hong E, Nodari D, Furlan F, et al., 2024, Strain-Induced α-Phase Stabilization for Low Dark Current FAPI-Based Photodetectors, Advanced Optical Materials
Formamidinium lead iodide (FAPbI3) has gained considerable interest as a promising photoactive layer for optoelectronic devices due to its broad spectrum of light absorption and increased thermal stability when compared to its conventional methylammonium counterpart (MAPbI3). Recent developments in substituting formamidinium (FA) with smaller Cs cations have further accelerated its growth in the photovoltaic (PV) community by enhancing phase stability and power conversion efficiency (PCE). However, only a few studies are reported on perovskite photodetectors (PPDs). Here, the influence of Cs incorporation is investigated on PD performance in the CsXFA1-XPbI3 system (X = 0–0.25). Finding that the partial substitution of FA with Cs cations alleviates lattice strain by increasing crystallinity and inducing a well-ordered surface morphology with vertical crystallographic orientation, which suppresses non-radiative recombination mechanisms. Such improved physicochemical properties of the mixed-cation perovskite light absorbers can improve the PD performance by reducing the dark and noise current to values as low as 3.3 × 10−9 A cm−2 and 6.1 × 1011 A Hz−1/2, thereby enabling PPDs with a faster photoresponse and greater sensitivity, which holds great promise for future optoelectronics applications.
Qiao Z, He Q, Scaccabarozzi AD, et al., 2024, A novel selenophene based non-fullerene acceptor for near-infrared organic photodetectors with ultra-low dark current, Journal of Materials Chemistry C, ISSN: 2050-7526
<jats:p>Organic photodetectors have great potential in near-infrared applications. Here we develop new non-fullerene acceptors with detection above 800 nm and demonstrated large area devices with record performances.</jats:p>
Huang Y-T, Nodari D, Furlan F, et al., 2023, Fast near-infrared photodetectors based on nontoxic and solution-processable AgBiS2, Small, ISSN: 1613-6810
Solution-processable near-infrared (NIR) photodetectors are urgently needed for a wide range of next-generation electronics, including sensors, optical communications and bioimaging. However, it is rare to find photodetectors with >300 kHz cut-off frequencies, especially in the NIR region, and many of the emerging inorganic materials explored are comprised of toxic elements, such as lead. Herein, solution-processed AgBiS2 photodetectors with high cut-off frequencies under both white light (>1 MHz) and NIR (approaching 500 kHz) illumination are developed. These high cut-off frequencies are due to the short transit distances of charge-carriers in the ultrathin photoactive layer of AgBiS2 photodetectors, which arise from the strong light absorption of this material, such that film thicknesses well below 120 nm are sufficient to absorb >65% of NIR to visible light. It is also revealed that ion migration plays a critical role in the photo-response speed of these devices, and its detrimental effects can be mitigated by finely tuning the thickness of the photoactive layer, which is important for achieving low dark current densities as well. These outstanding characteristics enable the realization of air-stable, real-time heartbeat sensors based on NIR AgBiS2 photodetectors, which strongly motivates their future integration in high-throughput systems.
Pan J, Chen Z, Zhang T, et al., 2023, Operando dynamics of trapped carriers in perovskite solar cells observed via infrared optical activation spectroscopy, Nature Communications, Vol: 14, ISSN: 2041-1723
Conventional spectroscopies are not sufficiently selective to comprehensively understand the behaviour of trapped carriers in perovskite solar cells, particularly under their working conditions. Here we use infrared optical activation spectroscopy (i.e., pump-push-photocurrent), to observe the properties and real-time dynamics of trapped carriers within operando perovskite solar cells. We compare behaviour differences of trapped holes in pristine and surface-passivated FA0.99Cs0.01PbI3 devices using a combination of quasi-steady-state and nanosecond time-resolved pump-push-photocurrent, as well as kinetic and drift-diffusion models. We find a two-step trap-filling process: the rapid filling (~10 ns) of low-density traps in the bulk of perovskite, followed by the slower filling (~100 ns) of high-density traps at the perovskite/hole transport material interface. Surface passivation by n-octylammonium iodide dramatically reduces the number of trap states (~50 times), improving the device performance substantially. Moreover, the activation energy (~280 meV) of the dominant hole traps remains similar with and without surface passivation.
Henderson C, Luke J, Bicalho I, et al., 2023, Charge transfer complex formation between organic interlayers drives light-soaking in large area perovskite solar cells, Energy and Environmental Science, Vol: 16, Pages: 5891-5903, ISSN: 1754-5692
Light soaking (LS) is a well-known but poorly understood phenomenon in perovskite solar cells (PSCs) which significantly affects device efficiency and stability. LS is greatly reduced in large-area inverted PSCs when a PC61BM electron transport layer (ETL) is replaced with C60, where the ETL is commonly in contact with a thin bathocuproine (BCP) interlayer. Herein, we identify the key molecular origins of this LS effect using a combination of surface photovoltage, ambient photoemission spectroscopy, Raman spectroscopy, integrated with density functional theory simulations. We find that BCP forms a photoinduced charge-transfer (CT) complex with both C60 and PC61BM. The C60/BCP complex accelerates C60 dimer formation, leading to a favourable cascading energetic landscape for electron extraction and reduced recombination loss. In contrast, the PC61BM/BCP complex suppresses PC61BM dimer formation, meaning that PC61BM dimerisation is not the cause of LS. Instead, it is the slow light-induced formation of the PC61BM/BCP CT complex itself, and the new energetic transport levels associated with it, which cause the much slower and stronger LS effect of PC61BM based PSCs. These findings provide key understanding of photoinduced ETL/BCP interactions and their impact on the LS effect in PSCs.
Vasilopoulou M, Mohd Yusoff ARB, Chai Y, et al., 2023, Neuromorphic computing based on halide perovskites, Nature Electronics, Vol: 6, Pages: 949-962
Neuromorphic computing requires electronic systems that can perform massively parallel computational tasks with low energy consumption. Such systems have traditionally been based on complementary metal–oxide–semiconductor circuits, but further advances in computational performance will probably require devices that can offer high-order complexity combined with area and energy efficiency. Halide perovskites can handle both ions and electronic charges, and could be used to create adaptive computing systems based on intrinsic device dynamics. The materials also offer exotic switching phenomena, providing opportunities for multimodal systems. Here we explore the development of neuromorphic hardware systems based on halide perovskites. We examine how devices based on these materials can serve as synapses and neurons, and can be used in neuromorphic computing networks. We also consider the challenges involved in developing practical perovskite neuromorphic systems, and highlight how these systems could augment and complement digital circuits.
Rimmele M, Qiao Z, Panidi J, et al., 2023, A polymer library enables the rapid identification of a highly scalable and efficient donor material for organic solar cells, Materials horizons, Vol: 10, Pages: 4202-4212, ISSN: 2051-6347
The dramatic improvement of the PCE (power conversion efficiency) of organic photovoltaic devices in the past few years has been driven by the development of new polymer donor materials and non-fullerene acceptors (NFAs). In the design of such materials synthetic scalability is often not considered, and hence complicated synthetic protocols are typical for high-performing materials. Here we report an approach to readily introduce a variety of solubilizing groups into a benzo[c][1,2,5]thiadiazole acceptor comonomer. This allowed for the ready preparation of a library of eleven donor polymers of varying side chains and comonomers, which facilitated a rapid screening of properties and photovoltaic device performance. Donor FO6-T emerged as the optimal material, exhibiting good solubility in chlorinated and non-chlorinated solvents and achieving 15.4% PCE with L8BO as the acceptor (15.2% with Y6) and good device stability. FO6-T was readily prepared on the gram scale, and synthetic complexity (SC) analysis highlighted FO6-T as an attractive donor polymer for potential large scale applications.
Savva A, Hama A, Herrera-Lopez G, et al., 2023, Photo-Chemical Stimulation of Neurons with Organic Semiconductors, ADVANCED SCIENCE
Xu W, Hart LJF, Moss B, et al., 2023, Impact of Interface Energetic Alignment and Mobile Ions on Charge Carrier Accumulation and Extraction in p-i-n Perovskite Solar Cells, ADVANCED ENERGY MATERIALS, Vol: 13, ISSN: 1614-6832
Qian D, Pratik SM, Liu Q, et al., 2023, Correlating the Hybridization of Local-Exciton and Charge-Transfer States with Charge Generation in Organic Solar Cells, ADVANCED ENERGY MATERIALS, ISSN: 1614-6832
Panidi J, Mazzolini E, Eisner F, et al., 2023, Biorenewable solvents for high-performance organic solar cells, ACS Energy Letters, Vol: 8, Pages: 3038-3047, ISSN: 2380-8195
With the advent of nonfullerene acceptors (NFAs), organic photovoltaic (OPV) devices are now achieving high enough power conversion efficiencies (PCEs) for commercialization. However, these high performances rely on active layers processed from petroleum-based and toxic solvents, which are undesirable for mass manufacturing. Here, we demonstrate the use of biorenewable 2-methyltetrahydrofuran (2MeTHF) and cyclopentyl methyl ether (CPME) solvents to process donor: NFA-based OPVs with no additional additives in the active layer. Furthermore, to reduce the overall carbon footprint of the manufacturing cycle of the OPVs, we use polymeric donors that require a few synthetic steps for their synthesis, namely, PTQ10 and FO6-T, which are blended with the Y-series NFA Y12. High performance was achieved using 2MeTHF as the processing solvent, reaching PCEs of 14.5% and 11.4% for PTQ10:Y12 and FO6-T:Y12 blends, respectively. This work demonstrates the potential of using biorenewable solvents without additives for the processing of OPV active layers, opening the door to large-scale and green manufacturing of organic solar cells.
Jacoutot P, Scaccabarozzi A, Nodari D, et al., 2023, Enhanced Sub-1 eV detection in organic photodetectors through tuning polymer energetics and microstructure, Science Advances, Vol: 9, Pages: 1-9, ISSN: 2375-2548
One of the key challenges facing organic photodiodes (OPD) is increasing the detection into the IR region. Organic semiconductor polymers provide a platform for tuning the bandgap and optoelectronic response to go beyond the traditional 1000 nm benchmark. In this work, we present a NIR polymer with absorption up to 1500 nm. The polymer-based OPD delivers a high specific detectivity D* of 1.03×1010 Jones (-2 V) at 1200 nm and a dark current Jd of just 2.3×10-6 A cm-2 at -2V. We demonstrate a strong improvement of all OPD metrics in the NIR region compared to previously reported NIR-OPD, due to the enhanced crystallinity and optimized energy alignment which leads to reduced charge recombination. The high D* value in the 1100-1300 nm region is particularly promising for biosensing applications. We demonstrate the OPD as a pulse oximeter under NIR illumination, delivering heart rate and blood oxygen saturation readings in real-time without signal amplification.
Zhao Y, Yang N, Chu X, et al., 2023, Wide-Humidity Range Applicable, Anti-Freezing, and Healable Zwitterionic Hydrogels for Ion-Leakage-Free Iontronic Sensors, ADVANCED MATERIALS, Vol: 35, ISSN: 0935-9648
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Ding B, Jo I-Y, Yu H, et al., 2023, Enhanced organic electrochemical transistor performance of donor-acceptor conjugated polymers modified with hybrid glycol/ ionic side chains by postpolymerization modification, Chemistry of Materials, Vol: 35, Pages: 3290-3299, ISSN: 0897-4756
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.
Anies F, Furlan F, Qiao Z, et al., 2023, A comparison of <i>para</i>, <i>meta</i>, and <i>ortho</i>-carborane centred non-fullerene acceptors for organic solar cells, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 11, Pages: 3989-3996, ISSN: 2050-7526
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Goudarzi H, Koutsokeras L, Balawi AH, et al., 2023, Microstructure-driven annihilation effects and dispersive excited state dynamics in solid-state films of a model sensitizer for photon energy up-conversion applications, CHEMICAL SCIENCE, Vol: 14, Pages: 2009-2023, ISSN: 2041-6520
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Cao Y, Mei J, Xia K, et al., 2023, Solution-based fullerene-free route enables high-performance green-selective organic photodetectors, JOURNAL OF PHYSICS-MATERIALS, Vol: 6
Ward MD, Shi W, Gasparini N, et al., 2022, Best practices in the measurement of circularly polarised photodetectors (vol 10, pg 10452, 2022), JOURNAL OF MATERIALS CHEMISTRY C, ISSN: 2050-7526
Furlan F, Nodari D, Palladino E, et al., 2022, Tuning Halide Composition allows low dark current perovskite photodetectors with high specific detectivity, Advanced Optical Materials, Vol: 10, Pages: 1-8, ISSN: 2195-1071
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.
Paleti SHK, Hultmark S, Ramos N, et al., 2022, Correlating Acceptor Structure and Blend Nanostructure with the Photostability of Nonfullerene Organic Solar Cells, SOLAR RRL, Vol: 6, ISSN: 2367-198X
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- Citations: 2
Vasilopoulou M, da Silva WJ, Soultati A, et al., 2022, Photonic nanostructures mimicking floral epidermis for perovskite solar cells, CELL REPORTS PHYSICAL SCIENCE, Vol: 3
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- Citations: 1
Kafourou P, Qiao Z, Toth M, et al., 2022, Low Dark Current Organic Photodetectors Utilizing Highly Cyanated Non-fullerene Acceptors, ACS APPLIED MATERIALS & INTERFACES, ISSN: 1944-8244
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- Citations: 2
Ward MD, Shi W, Gasparini N, et al., 2022, Best practices in the measurement of circularly polarised photodetectors, JOURNAL OF MATERIALS CHEMISTRY C, Vol: 10, Pages: 10452-10463, ISSN: 2050-7526
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- Citations: 6
Zhang T, Gasparini N, 2022, Ternary organic solar cells: Insights into charge and energy transfer processes, APPLIED PHYSICS LETTERS, Vol: 120, ISSN: 0003-6951
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- Citations: 3
Zhang T, Gregoriou VG, Gasparini N, et al., 2022, Porous organic polymers in solar cells, CHEMICAL SOCIETY REVIEWS, Vol: 51, Pages: 4465-4483, ISSN: 0306-0012
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- Citations: 15
Jacoutot P, Scaccabarozzi AD, Zhang T, et al., 2022, Infrared organic photodetectors employing ultralow bandgap polymer and non-fullerene acceptors for biometric monitoring, Small, Vol: 18, Pages: 1-10, ISSN: 1613-6810
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.
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