Emerging technologies benefit from a jointly established reference protocol, which can lower the bar of entry for new researchers while serving as a calibration standard for established actors. The light-emitting electrochemical cell (LEC) combines electrochemistry and optoelectronics in an intricate manner, and it can by that enable sustainable and commercially relevant printing fabrication of emissive thin-film devices. However, LEC performance is sensitive to a range of material and processing parameters, which frequently results in inadequate, or even erroneous, device evaluation. With this in mind, we present herein a LEC reference protocol, which details the sourcing of materials and the procedures and parameters for robust device fabrication and operation. The protocol has been tested across nine international research groups, and the collected results from this interlaboratory round-robin test confirm that good LEC performance can be reproducibly obtained following our protocol. We also identify common pitfalls that can arise during LEC development, and present practical steps for attaining optimum LEC performance. We hope this reference protocol will improve the quality of future LEC research and serve as a guide for future researchers entering this vibrant field.

Near-infrared (NIR) light detection at wavelengths λ > 1100 nm is essential in modern science and technology. Emerging organic semiconductors are promising for solution-processed, flexible, and large-area NIR organic photodetectors (OPDs), but only a few organic chromophores with peak absorption beyond the silicon bandgap are available. Furthermore, the external quantum efficiency (EQE) and specific detectivity (D*) of NIR OPDs are restricted by insufficient exciton dissociation and high dark/noise current. Here, the combination of strong electron-accepting and -donating groups is used to synthesize a selection of novel NIR squaraine dyes with superior redshifted absorptions, peaking at 1165 nm in solution and extending to 1240 nm in a blend film. To overcome the tradeoff between long wavelength absorption and high photoresponse, NIR photons are detected utilizing a gain OPD design, where photomultiplication occurs via squaraine hole trap-induced injection of external charges. The OPD can achieve an EQE of 220% at 1240 nm and still maintains 25% in the absorption tail at 1400 nm, thereby surpassing existing NIR OPDs in a broad wavelength range beyond 1100 nm. The measured maximum D* equals 109 Jones at 1240 nm, and the detectivity estimated from the shot noise is ≈1011 Jones, independent of the bias voltage.

Tin perovskites are emerging as promising alternatives to their lead-based counterparts for high-performance and flexible perovskite solar cells. However, their rapid crystallization often leads to inadequate film quality and poor device performance. In this study, the role of GeI2 as an additive is investigated for controlling the nucleation and crystallization processes of formamidinium tin triiodide (FASnI(3)). The findings reveal the preferential formation of a Ge-rich layer at the bottom of the perovskite film upon the introduction of GeI2. It is proposed that the initial formation of the Ge complex acts as a crystallization regulator, promoting oriented growth of subsequent FASnI(3) crystals and enhancing overall crystallinity. Through the incorporation of an optimal amount of GeI2, flexible Sn perovskite solar cells with an efficiency of 10.8% were achieved. Furthermore, it was observed that the GeI2 additive ensures a remarkable shelf-life for the devices, with the rigid cells retaining 91% of their initial performance after more than 13 800 h of storage in an N-2 gas environment. This study elucidates the mechanistic role of GeI2 in regulating the nucleation and crystallization process of tin perovskites, providing valuable insights into the significance of additive engineering for the development of high-performance flexible tin perovskite solar cells.

The alarming rise in global temperature mandates the reduction of carbon emissions. Along with the usage of clean energy technologies, removal of the existing/produced CO 2 in the atmosphere is also equally important to mitigate climate change. Amine-based sorbents are most popular for absorbing CO 2 from the atmosphere as well as industrial flue gas. However, the regeneration of amines is an energy-intensive process that limits their applicability [1]. Electrochemically mediated CO 2 capture/release (EMCCR) offers a significant advantage in terms of energy requirement and design considerations. Anthraquinone (AQ) derivatives are commonly used as a redox mediator in EMCCR. Reduced AQ has an affinity to bind with CO 2 and facilitate its release upon oxidation, allowing the shuttling of CO 2 between reduced and neutral AQ [2]. In all the reported studies, either dissolved form of CO 2 in an electrolyte or gaseous CO 2 that must diffuse through a porous electrode is captured (released) via redox active molecule reduction (oxidation) [3]. This poses problems regarding the solubility of CO 2 in electrolytes and the mass transfer of CO 2 through electrodes, which are key limiting parameters for EMCCR. In addition, the solubility of AQ in the electrolyte also restricts the CO 2 -capturing capability. Against this background, fresh impetus was given with CNT-based slurry electrodes that have the potential to bypass the solubility issue of CO 2 and also its diffusion limitation , thereby resulting in efficient EMCCR. Slurry electrodes are commonly composed of conductive molecules for electrons to flow, redox species that get reduced/oxidized upon electron transfer, and the electrolyte for ionic mobility [4]. In the present work, CNT is a conductive part, AQ molecules are redox active species, and the ionic liquid (IL), 1-butyl-3-methylimidazolium bis(trifluoromethyl sulfonyl) imide is the electrolyte. The concept is demonstrated by subjecting the CNT slurry electrode to electrochemical characterization in a three-electrode setup under N 2 and CO 2 environments. Figure 1 shows the cyclic voltammogram (CV) of the CNT slurry electrode in a potential window of -1.25 to 1.25 V vs. FC + /FC at a scan rate of 50 mV/s. Two reduction/oxidation peaks for a CV under N 2 are observed. In contrast, merged reduction/oxidation peaks with increased current in cathodic peak under CO 2 reveal that CO 2 is captured during reduction and released during oxidation [2]. Further, three different weight ratios of CNT to AQ were studied to understand the effect of CNT solid content on the electrochemical performance of slurry electrodes for EMCCR. Accordingly, 50:1, 100:1, and 150:1 ratios of CNT to AQ were chosen, which resulted in solid contents of 2.1, 4.2 and 6.3%. Lower solid content showed improved electrochemical reversibility for AQ molecules. In practice, one must consider the required viscosity and conductivity of the slurry to make it productive as an efficient flow electrode while fixing the solid content. Since the CNT to AQ weight ratio is considered for evaluating performance, the solubility of AQ in IL inherently limits the solid content. It is also worth noting that the solubility of AQ is very low (in the order of 1 to 4 mM) in IL. To this end, efforts were also invested in modifying the AQ molecule to push its solubility in the IL. AQ was functionalized with imidazolium side chains to produce functionalized AQ (FAQ) that mimics the chemical structure of the IL. The same ratios that are used earlier, would result in different solid contents owing to the increased solubility of FAQ. Similar studies were also conducted on slurry electrodes comprising FAQ to establish the best weight ratio and solid content for improved electrochemical activity. Additionally, batch-mode single-cell investigations with real time monitoring of CO 2 were performed to shed light on CO 2 capture/release capabilities of CNT-based slurry electrodes. References: Rheinhardt, J. H., Singh, P., Tarakeshwar, P., & Buttry, D. A. (2017). Electrochemical capture and release of carbon dioxide. ACS Energy letters, 2(2), 454-461. Gurkan, B., Simeon, F., & Hatton, T. A. (2015). Quinone reduction in ionic liquids for electrochemical CO2 separation. ACS Sustainable Chemistry & Engineering , 3 (7), 1394-1405. Voskian, S., & Hatton, T. A. (2019). Faradaic electro-swing reactive adsorption for CO 2 capture. Energy & Environmental Science , 12 (12), 3530-3547. Mourshed, M., Niya, S. M. R., Ojha, R., Rosengarten, G., Andrews, J., & Shabani, B. (2021). Carbon-based slurry electrodes for energy storage and power supply systems. Energy Storage Materials , 40 , 461-489. Figure 1

Already in 2012, Blom et al. reported (Nature Materials 2012, 11, 882) in semiconducting polymers on a general electron-trap density of approximate to 3 x 10(17) cm(-3), centered at an energy of approximate to 3.6 eV below vacuum. It was suggested that traps have an extrinsic origin, with the water-oxygen complex [2(H2O)-O-2] as a possible candidate, based on its electron affinity. However, further evidence is lacking and the origin of universal electron traps remained elusive. Here, in polymer diodes, the temperature-dependence of reversible electron traps is investigated that develop under bias stress slowly over minutes to a density of 2 x 10(17) cm(-3), centered at an energy of 3.6 eV below vacuum. The trap build-up dynamics follows a 3(rd)-order kinetics, in line with that traps form via an encounter between three diffusing precursor particles. The accordance between universal and slowly evolving traps suggests that general electron traps in semiconducting polymers form via a triple-encounter process between oxygen and water molecules that form the suggested [2(H2O)-O-2] complex as the trap origin. [GRAPHICS] .

Organic upconverters made by integrating an infrared-sensitive photodetector with a light-emitting diode offer a low-cost route to visualize images taken in the infrared. However, making such devices sufficiently efficient is challenging. Here, upconversion devices are demonstrated with an efficiency of 13.9% for converting infrared photons (980 nm, 5 mW cm-2) to visible photons (575 nm). Infrared photons are detected with a photomultiplication photodetector that includes a copper thiocyanate electron-blocking/injection layer and an infrared-sensitive squaraine dye dispersed (3 wt-%) in a fullerene matrix. At turn-on, the detector achieves an external quantum efficiency of 1200% (at 1020 nm, -10 V, 44 mu W cm-2). Photomultiplication occurs via hole trap-induced injection of electrons. In the upconverter, these electrons are driven into the emitter and recombine with holes under visible light emission. During operation the photodetector current increases because, presumably, rearranging mobile ions in copper thiocyanate narrows the injection barrier. Thereby, the upconverter photoconversion efficiency gradually increases to 18.7%. The performance of the present upconverter is limited by the not-yet-ideal charge-blocking/injection layer, which is too thick and blocks electrons in the dark insufficiently. With thin and compact charge-blocking layers at hand, the device concept paves the way for widespread use in sensitive infrared imaging. Organic upconversion devices are demonstrated by integrating a shortwave infrared-sensitive, squaraine dye-based photomultiplication photodetector with a visible light-emitting diode. Photomultiplication occurs via squaraine hole trap-induced injection of electrons. The photoinduced injection of multiple charges into the emitter boosts the efficiency to over 18% for converting infrared to visible photons. image

It is widely accepted that mobile ions are responsible for the slow electronic responses observed in metal halide perovskite-based optoelectronic devices, and strongly influence long-term operational stability. Electrical characterisation methods mostly observe complex indirect effects of ions on bulk/interface recombination, struggle to quantify the ion density and mobility, and are typically not able to fully quantify the influence of the ions upon the bulk and interfacial electric fields. We analyse the bias-assisted charge extraction (BACE) method for the case of a screened bulk electric field, and introduce a new characterisation method based on BACE, termed ion drift BACE. We reveal that the initial current density and current decay dynamics depend on the ion conductivity, which is the product of ion density and mobility. This means that for an unknown high ion density, typical in perovskite solar absorber layers, the mobility cannot be directly obtained from BACE measurements. We derive an analytical model to illustrate the relation between current density, conductivity and bulk field screening, supported by drift-diffusion simulations. By measuring the ion density independently with impedance spectroscopy, we show how the ion mobility can be derived from the BACE ion conductivity. We highlight important differences between the low- and high-ion density cases, which reveal whether the bulk electric field is fully screened or not. Our work clarifies the complex ion-related processes occurring within perovskite solar cells and gives new insight into the operational principles of halide perovskite devices as mixed ionic-electronic conductors.

Stretchable alternating current electroluminescent (ACEL) devices have a bright future in wearable electronics and soft robotics. Still, their market application is hindered by high operating voltages. The voltage can be reduced by increasing the relative permittivity of the dielectric elastomer in the emissive layer. Here, a fluorine-free high-permittivity silicone elastomer functionalized with cyanopropyl side groups, specially designed for application in stretchable ACEL devices, is introduced. The polar silicone elastomer exhibits excellent mechanical properties and a dielectric permittivity four times higher than commercial PDMS. Light-emitting devices based on the polar elastomer reach 7.5 times higher maximum luminance at the same electric field than PDMS-based devices and turn on at a 50% lower electric field. Besides, the polar elastomer-based devices perform better than all materials tested in literature in achieving high luminance at low electric fields. Stretchable ACEL devices are built from the polar elastomer which shows bright and uniform light emission and can be operated up to 50% strain. The high-permittivity silicones are promising materials for stretchable ACEL devices and can help their breakthrough to market application by overcoming the drawback of high operating voltages. A high-permittivity, nitrile-functional silicone elastomer for application in stretchable electroluminescent devices is introduced. The polar elastomer emissive layer reaches significantly higher luminance and needs lower operating voltages than an emissive layer based on commercially available PDMS. Besides, the polar elastomer can be used to build bright and stretchable devices in a simple bottom-up procedure. image

Sensitive detection of shortwave infrared (SWIR) light using organic dyes will be a significant advance toward many applications in industry and research. Furthermore, from a fabrication and optimization view, photogeneration of charges in diodes consisting of a single dye layer will be highly attractive. However, SWIR dyes are scarce and organic photodiodes usually utilize a donor-acceptor materials combination to split excitons into charges. Here, it is demonstrated that single-component layers of several SWIR squaraine dyes operate as efficient photodetectors, with peak external quantum efficiency > 40% beyond 1000 nm and sensitivity out to 1300 nm. Photocurrents show a superlinear dependence on reverse bias. It is shown that this results from a field-assisted exciton dissociation mechanism, and not from field-dependent charge injection or extraction. SWIR photodiodes are combined with organic light-emitting diodes to fabricate upconversion photodetectors - devices that convert SWIR photons directly into visible light. Upconverters are characterized by a low turn-on voltage (1.5 V) and a high luminance contrast (on-off ratio 16 000) and SWIR-to-visible (lambda = 575 nm) photon conversion efficiency (1.85%). Upconversion photodetectors emerge as a promising alternative to the current inorganic-based imaging technology.

Strongly polarized donor-acceptor-donor ' diketopyrrolopyrroles, differing in the type of key donor moiety, were designed and synthesized to examine how this affects the non-radiative decay. Dyes possessing less electron-rich N-carbazolyl substituents are characterized by strong yellow emission from a locally excited (LE) state, whereas replacing this donor with more electron-rich N-phenothiazinyl substituent changes the relative position of charge-transfer (CT) and LE states, leading to weaker, reddish-orange fluorescence. As a result, there is solvent-dependent charge-transfer emission shifted to as far as 700 nm. The opening of the intersystem crossing channel to the triplet state possessing CT character is the most likely cause of the fluorescence quantum yield variation in some cases. These results reveal that the fate of molecules in their excited state can be fine-tuned by very small structural changes. Modulation of strength and position of electron-donating substituent directly linked to a diketopyrrolopyrrole core offers an interesting approach towards fine-tuning their photophysics. Depending on the type of cyclic tertiary aromatic amine either Franck-Condon or charge-transfer excited states have the lowest energy. The N-carbazolyl substituent enables DPPs to have very strong fluorescence while other donors such as phenothiazine red-shift the emission at the expense of quantum yield.image

Organic upconversion devices (OUCs) consist of an organic infrared photodetector and an organic visible light‐emitting diode (OLED), connected in series. OUCs convert photons from the infrared to the visible and are of use in applications such as process control or imaging. Many applications require a fast OUC response speed, namely the ability to accurately detect in the visible a rapidly changing infrared signal. Here, high image‐contrast, narrowband OUCs are reported that convert near‐infrared (NIR) light at 980 and 976 nm with a full‐width at half maximum of 130 nm into visible light. Transient photocurrent measurements show that the response speed decreases when lowering the NIR light intensity. This is contrary to conventional organic photodetectors that show the opposite speed‐versus‐light trend. It is further found that the response speed increases (when using a phosphorescent OLED) or decreases (for a fluorescent OLED) when increasing the driving voltage. To understand these surprising results, an analysis by numerical simulation is conducted. Results show that the response speed behavior is primarily determined by the electron mobility in the OLED. It is proposed that the low electron drift velocity in the emitter layer sets a fundamental limit to the response speed of OUCs.

Polymer light‐emitting electrochemical cells (PLECs) and light‐emitting diodes (PLEDs) receive interest for large‐area lighting and signage applications. During operation of a PLEC, a p–i–n junction develops where electrons and holes are injected into the film and are transported along n ‐ and p ‐doped regions to the intrinsic ( i ) region, where they recombine under light emission. Conceptually, this resembles the PLED device architecture equipped with Ohmic charge‐injection and transport layers. The similarity between the i ‐region of the PLEC and the emissive layer of the PLED is obvious; however, implication of this has not been examined in detail so far. For example, for PLEDs it is known that electron traps hinder the electron transport, and that hole trap formation dictates the long‐term durability. Here, for PLECs the electrical and optical response to electrical driving and breaks are studied, the current response to external light irradiation is probed, and degradation is followed with long‐term absorption and capacitance measurements. The electron traps in PLECs are identified and it is found that hole trap formation limits the device lifetime, in the same manner as established for PLEDs. It is concluded that charge traps in semiconducting polymers present important, but so far overlooked intrinsic performance limitations for PLECs.

Semiconducting polymers are being studied intensively for optoelectronic device applications, including solution‐processed light‐emitting diodes (PLEDs). Charge traps in polymers limit the charge transport and thus the PLED efficiency. It is firmly established that electron transport is hindered by the presence of the universal electron trap density, whereas hole trap formation governs the long‐term degradation of PLEDs. Here, the response of PLEDs to electrical driving and breaks covering the timescale from microseconds to (a few) hours is studied, thus focusing on electron traps. As reference polymer, a phenyl‐substituted poly(para‐phenylene vinylene) (PPV) copolymer termed super yellow (SY) is used. Three different traps with depths between ≈0.4 and 0.7 eV, and a total trap site density of ≈2 × 1017 cm−3 are identified. Surprisingly, filling of deep traps takes minutes to hours, at odds with the common notion that charge trapping is complete after a few hundred microseconds. The slow trap filling feature for PLEDs is confirmed using poly(2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene (MEH‐PPV) and poly(3‐hexylthiophene) (P3HT) as active materials. This unusual phenomenon is explained with trap deactivation upon detrapping and slow trap reactivation. The results provide useful insight to pinpoint the chemical nature of the universal electron traps in semiconducting polymers.

We conducted a global survey on the effects of the COVID-19 pandemic on the research activities of materials scientists by distributing a questionnaire on 9 October 2020 with a response deadline of 23 October 2020. The questions covered issues such as access to labs, effectiveness of online conferences, and effects on doctoral students for the period covering the first lockdowns until the relaxation of restrictions in late September 2020 in many countries. The survey also included online interviews with eminent materials scientists who shared their local experiences during this period. The interviews were compiled as a series of audio conversations for The STAM Podcast that is freely available worldwide. Our findings included that the majority of institutes were not prepared for such a crisis; researchers in China, Japan, and Singapore were able to resume research much quicker – for example after approximately one month in Japan – than their counterparts in the US and Europe after the first lockdowns; researchers adapted to using virtual teleconferencing to maintain contact with colleagues; and doctoral students were the hardest hit by the pandemic with deep concerns about completing their research and career prospects. We hope that the analysis from this survey will enable the global materials science community to learn from each other’s experiences and move forward from the unprecedented circumstances created by the pandemic.

Charge transfer (CT) states play a key role in the functioning of organic solar cells; however, understanding the mechanism by which CT states dissociate efficiently into free charges remain a conceptual challenge. Here, the electric field dependent dynamics of charge generation in planar cyanine/fullerene photovoltaic cells is probed over a wide temperature range using time‐resolved Stark effect experiments, transient absorption, and photocurrent measurements. Results indicate that dissociation of thermalized CT states is the rate‐limiting step for all temperatures. The dissociation rate strongly depends on the field, but is temperature independent. The results also suggest that the yield of generated charges is temperature independent. Model electrostatic calculations illustrate that specific orientations of the cyanine crystal relative to C 60 create a repulsive potential for an electron near the interface that is largely due to the quadrupole moment of the unit cell. In combination with the electron‐hole coulomb attraction and the electric field‐induced barrier lowering, a high‐energy potential barrier forms with a narrow width of a few nanometers. It is proposed that charge separation occurs via a field‐dependent electron tunneling mechanism through that barrier, which is temperature independent. The results support a thus far overlooked pathway for CT state dissociation via carrier tunneling.

Achieving fundamental understanding of enantioselective heterogeneous synthesis is marred by the permanent presence of multitudinous arrangements of catalytically active sites in real catalysts. In this study, we address this issue by using structurally comparatively simple, well-defined, and chiral intermetallic PdGa{111} surfaces as catalytic substrates. We demonstrate the impact of chirality transfer and ensemble effect for the thermally activated azide-alkyne Huisgen cycloaddition between 3-(4-azidophenyl)propionic acid and 9-ethynylphenanthrene on these threefold symmetric intermetallic surfaces under ultrahigh vacuum conditions. Specifically, we encounter a dominating ensemble effect for this reaction as on the Pd3-terminated PdGa{111} surfaces no stable heterocoupled structures are created, while on the Pd1-terminated PdGa{111} surfaces, the cycloaddition proceeds regioselectively. Moreover, we observe chirality transfer from the substrate to the reaction products, as they are formed enantioselectively on the Pd1-terminated PdGa{111} surfaces. Our results evidence a determinant ensemble effect and the immense potential of PdGa as asymmetric heterogeneous catalyst.

Shortwave infrared (SWIR) optical sensing and imaging are essential to an increasing number of next-generation applications in communications, process control or medical imaging. An all-organic SWIR upconversion device (OUC) consists of an organic SWIR sensitive photodetector (PD) and an organic light-emitting diode (OLED), connected in series. OUCs directly convert SWIR to visible photons, which potentially provides a low-cost alternative to the current inorganic compound-based SWIR imaging technology. For OUC applications, only few organic materials have been reported with peak absorption past 1000 nm and simultaneous small absorption in the visible. Here, we synthesized a series of thermally stable high-extinction coefficient donor-substituted benz[cd]indole-capped SWIR squaraine dyes. First, we coupled the phenyl-, carbazole-, and thienyl-substituted benz[cd]indoles with squaric acid (to obtain the SQ dye family). We then combined these donors with the dicyanomethylene-substituted squaraine acceptor unit, to obtain the dicyanomethylene-functionalized squaraine DCSQ family. In the solid state, the absorbance of all dyes extended considerably beyond 1100 nm. For the carbazole- and thienyl-substituted DCSQ dyes, even the peak absorptions in solution were in the SWIR, at 1008 nm and 1014 nm. We fabricated DCSQ PDs with an external photon-to-current efficiency over 30%. We then combined the PD with a fluorescent OLED and fabricated long-term stable OUCs with peak sensitivity at 1020 nm, extending to beyond 1200 nm. Our OUCs are characterized by a very low dark luminance (<10−2 cd m−2 at below 6 V) in the absence of SWIR light, and a low turn-on voltage of 2 V when SWIR light is present.

Solution-processed lead sulfide quantum dots (PbS QDs) are very attractive as NIR-active semiconductors for the fabrication of cost-efficient optoelectronic devices. To control the thin film carrier transport, as well as stability, surface passivation is of crucial importance. Here, we present the successful surface passivation of PbS QDs by the formamidinium lead iodide (FAPbI3) ligand. An effective procedure for the fabrication of FAPbI3-passivated PbS QDs through a binary-phase ligand exchange protocol in hexane and n-methylformamide is demonstrated. It is shown that this solution-processed ligand exchange drastically changes the photoluminescence intensity, exciton recombination dynamics, and carrier lifetime of the nanocrystals. The solution casting of the ligand-exchanged nanocrystals into thin films results in the periodic ordering of QDs in a square superlattice with close contacts. Planar graphene/QD photodetectors fabricated with PbS QDs passivated with FAPbI3 show substantially increased thermal stability as compared to similar devices using PbS QDs passivated with commonly used methylammonium lead iodide.

In light‐emitting electrochemical cells (LECs), the position of the emission zone (EZ) is not predefined via a multilayer architecture design, but governed by a complex motion of electrical and ionic charges. As a result of the evolution of doped charge transport layers that enclose a dynamic intrinsic region until steady state is reached, the EZ is often dynamic during turn‐on. For thick sandwich polymer LECs, a continuous change of the emission color provides a direct visual indication of a moving EZ. Results from an optical and electrical analysis indicate that the intrinsic zone is narrow at early times, but starts to widen during operation, notably well before the electrical device optimum is reached. Results from numerical simulations demonstrate that the only precondition for this event to occur is that the mobilities of anions ( μ a ) and cations ( μ c ) are not equal, and the direction of the EZ shift dictates μ c > μ a . Quantitative ion profiles reveal that the displacement of ions stops when the intrinsic zone stabilizes, confirming the relation between ion movement and EZ shift. Finally, simulations indicate that the experimental current peak for constant‐voltage operation is intrinsic and the subsequent decay does not result from degradation, as commonly stated.

Strongly coupled dye molecules are known to produce narrowband absorption in a large spectral range. Here we exploit this feature to achieve organic photodetectors with ultra-narrow full-width at half-maximum response at low bias voltage.