Organic photodetectors (OPDs) with a performance comparable to that of conventional inorganic ones have been demonstrated for the visible wavelength regime. However, near-infrared (NIR) photodetection has proven to be challenging and, to date, the true potential of organic semiconductors in this spectral range (800–2500 nm) remains largely unexplored. In this talk, I will introduce new device concepts for organic NIR detectors, based on resonant optical cavities and doped photo-active layers. Design rules and optimization strategies will be discussed, yielding wavelength selective devices (20 nm resolution) with a tunability of the detection wavelength over several hundreds of nanometers, allowing the printing of miniature NIR spectrometers. In a second part of the talk, we explore the performance limitations of organic NIR detectors: A relation between open-circuit voltage, dark current, and noise current is demonstrated for OPDs with detection wavelengths beyond 1100 nm. Based on these findings we estimate an upper limit of achievable specific detectivity values for organic photodiodes as a function of their longest NIR detection wavelength.

Near-infrared organic photodetectors (OPDs) experienced a fast growth in recent years owing to their advantages over traditional inorganic photodetectors. By fine-tuning the optical bandgap of the organic material, OPDs can be engineered for high and specific light detection. In particular, the advent of non-fullerene acceptors (NFAs), with tunable energy levels, allowed OPDs with light detection in the near-infrared (NIR) region.

Analyzing the structures of reported NFAs, many of the best performing contain thiophene-based fused aromatics within the donor core. A strategy to shift the absorption windows is to replace the thiophene moiety with selenophene. Selenophene has lower aromatic stabilization energy than thiophene and will increase the quinoidal character of the material.

Until now, few fused selenophene containing NFAs containing straight chain alkyl groups have been reported. The replacement of the alkyl aryl groups with straight chain alkyl groups will change the solid-state microstructure of thiophene-based NFAs and then enhance the power conversion efficiency (PCE). In this work, we report the first NFA containing a fused indacenodiselenophene with octyl sidechains at the bridgehead positions. This is the direct selenophene analogue of the previously indacenodithiophene acceptor known as IDIC, which has been widely reported in the OPV community.

Herein we show that the selenophene analogue IDSe exhibits a red-shifted absorption compared to the thiophene analogue IDIC, and when paired with a suitable wide band gap donor PTQ10, organic photodetector devices using a bulk heterojunction configuration have an ultralow dark current density (J_d) of 1.65×10^-9 A cm^-2 at -2V and a specific detectivity (D*) of 10¹² Jones at -2V bias. With a combination of optoelectronic measurements, transient analyses and morphological investigations based on GIWAXS measurements, we attributed the low J_d of the PTQ10:IDSe blend to the higher and more balanced carrier mobilities compared to the thiophene benchmark. In addition, we fabricated large-area OPDs (5x5 cm substrates) using doctor blade coating in air and obtained extraordinarily low dark current, indicating its ability to be large-scaled processed in the future.

Planner hetero-junction (PHJ) structure is one of the key device fabrication strategies to increase specific detectivity by reducing dark current in organic photodiodes (OPDs). We demonstrated that efficient free charge generation in partially chlorinated subphthalocyanine molecules (Cl6-SubPc) can assist PHJ OPDs to achieve detectivity up to 1013 Jones and dark current below 10-7 A cm-2 up to -5 V. The photophysical analysis of Cl6-SubPc based devices clearly show that device photocurrent is primarily generated through direct charge generation within the Cl6-SubPc layer, rather than exciton separation at layer interfaces. Molecular modelling suggests that direct charge generation is facilitated by Cl6-SubPc’s high octupole moment which generates a shift in molecular energetics ­­[1,2] (Fig(1(a)). Also, lower trap densities analysed from capacitance-frequency response [3] in thick PHJ device helps in further minimising leakage currents as shown in Fig(1(b)). In summary, this study provides clear indication that Cl6-SubPc is promising material for single component OPD devices.

Photodiodes based on organic semiconductors exhibit many advantageous properties including tailorable light absorption, low embodied energy manufacturing, structural conformality, and low material toxicity. These properties make organic photodiodes attractive for emerging photodetector applications, especially for novel applications requiring different optoelectronic and mechanical properties than provided by conventional photodiodes based on inorganic semiconductors.[1] However, thus far the specific detectivity of organic photodiodes has remained subpar relative to conventional photodiodes. A critical parameter limiting the specific detectivity of photodiodes is the dark saturation current. In organic photodiode devices, the dark saturation current is strongly limited by non-radiative processes resulting in dark saturation currents several orders of magnitude higher than expected for radiative band-to-band transitions; however, the origin of these non-radiative processes is still debated. In this work, we show that the dark saturation current, along with the specific detectivity, in organic photodiode devices is fundamentally limited by transitions via mid-gap trap states.[2] This new insight is generated by a universal trend observed for a large set of organic bulk heterojunction systems and substantiated by sensitive external quantum efficiency and temperature-dependent current measurements. These findings have important implications for organic photodiodes, providing new insight into the origin of non-radiative losses and the associated noise, establishing the performance limits for these devices. 

Solution-processed metal halide perovskite photodetectors (PPDs) have a great potential in visible and near-infrared light sensing and X-ray imaging applications, owing to their excellent optoelectronic properties. This presentation will consist of two parts. After a brief survey of the advantages of solution-processed perovskites in high-resolution, flexible large-area imagers we will focus on better understanding the physical mechanisms that determine the dark current density and detectivity of thin-film photodetectors in the first part [1].

We will demonstrate that extrinsic leakage current at the periphery of the bottom pixel electrode is greatly reduced by introducing a so-called pixel edge cover layer. When such an edge cover layer is inserted, the dark current density decreases to ~10−6 mA cm−2 at −0.5 V, which is among the lowest values reported for polycrystalline PPDs.1 Moreover, the dark current density becomes independent of pixel size, up to 1000 ppi. To reduce dark current density even further, we carefully investigated a range of charge blocking layers, effectively reducing the dark current density even further.

By combining the appropriate blocking layer with the edge cover, a perovskite thin-film photodiode was fabricated that has a spectral responsivity of 0.5 A/W at 950 nm (Fig. 1a), combined with an ultralow dark current density of 5 × 10−8 mA cm−2 (Fig. 1b) and noise current of 2 × 10−14 A Hz−1/2 .

In the second part we will present recent developments in realizing three prototypical applications, i.e. a paper-thin photo-imager [2], a direct conversion X-ray detector [3] and a novel narrowband optical sensor that can measure a person’s heartbeat and respiration rate from a distance of over one meter using NIR light [4].

Including thin-film encapsulation layers - required to guarantee a long lifetime - the photo-imager [2] is only ca. 100 mm thick and can be wrapped around a non-flat object (radius of curvature of 0.6 cm). The wrapping ensures the close proximity between sensor surface area and a curved object, effectively increasing the area of the object that can be imaged with high-resolution. This is relevant for instance for nail-to-nail fingerprint imaging. Biometric fingerprinting is demonstrated with liveness detection.

The resulting direct-conversion X-ray detector [3] has a low detection limit of 0.22 nGyair frame-1, a sensitivity of 1060 µCGyair-1cm-2 (at a bias of 0.03 V µm−1) with a high spatial resolution of 6 line-pairs mm-1.

Finally, we report an inherently-narrowband solution-processed, thin-film photodiode with ultrahigh and controllable NIR responsivity based on a tandem-like perovskite-organic architecture [4]. The device possesses low dark currents (< 10−6 mA cm−2), linear dynamic range > 150 dB, and operational stability over time (> 8 h). With a narrowband quantum efficiency that can exceed 200% at 850 nm and intrinsic filtering of other wavelengths to limit optical noise, the device exhibits higher tolerance to background light than optically-filtered silicon-based sensors.

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 have been reported on perovskite photodetectors (PPDs). Here, we investigate the influence of Cs incorporation on PD performance in the Cs_XFA_1-XPbI₃ system (X = 0–0.25). We demonstrate that A-site substitution with Cs reduces microstrain within the crystal lattice and promotes the formation of a compact, well-ordered surface with improved morphology. To evaluate the performance of the Cs_XFA_1-XPbI₃ system, we have prepared p-i-n photodiode-type PDs using a one-step spin-coating method. We find that the lattice strain relaxation considerably reduces the Jd in the device, which may be partially due to the reduction in lattice strain which reduces trap density and improves charge transport. Particularly, the lowest Jd value of 3.3x10^-9 A cm^-2 is achieved for Cs_0.05FA_0.95PbI₃ at -0.5 V, which also greatly contributes to its highest specific detectivity of 6.1x10¹¹ A Hz^-1/2 and widest linear dynamic range of 135 dB. Furthermore, when this mixed-cation perovskite material is integrated into a device, long-term stability without sacrificing performance is observed, which holds great promise for future optoelectronics applications.

Lead halide perovskite and organic semiconductors have been promising classes of materials for photodetector (PD) applications. However, despite their high performances with low noise and specific detectivity (D*) values exceeding the one of silicon detectors, perovskite PDs working regime is limited to the visible and the first fraction of near-infrared (NIR) spectrum due to their bandgap.1,2 Differently, organic PDs have the advantage of tunable absorption thanks to their chemical design. In this work, we fabricated perovskite-organic heterojunction (POH) PDs with extended absorption up to 900 nm, thanks to the deposition of a donor:acceptor bulk-heterojunction (BHJ) layer on top of the perovskite. We systematically studied the effect of the energetic of the donor materials on the dark current (Jd) of the device by using polymers from the PBDB-T family (PCE12, PM6 and PM7). By using this approach, PM7-based POH delivered ultra-low noise of 2 x 10-14 A Hz-1/2 and high specific detectivity D* of 4.7 x 1012 Jones (-0.5 V) at 840 nm. This was achieved by increasing the energetic barrier between the HOMO of the donor and the LUMO of the acceptor as explained by our analytical model.3 We found that the donor sites effectively act as recombination centres at the perovskite/BHJ interface, affecting Jd. In particular, PM7 with a deeper HOMO level, formed a larger LUMO(Y6)-HOMO(D) gap compared to PM6. This resulted in a smaller contribution of the HOMO of the donor to the dark current, similar to the intrinsic traps introduced by Y6 at perovskite/BHJ interface.

Printing technology is set to enable the high-throughput low-cost and customized fabrication of optoelectronic and sensors devices. For this goal to become a reality, this functional printing approach should encompass a material process development which enables high device performance and industrial compatibility, thus enabling a facile transfer of research results into consumer applications.

In this contribution, I will present the fabrication of fully printed organic photodiodes (OPDs) by digital printing techniques (e.g. aerosol and inkjet). The devices show mechanical flexibility, semitransparency and an excellent reproducibility. I will discuss the use of the ink formulation as way to access and tailor material optoelectronic properties. In this direction, we have focused on the control of the molecular order in organic semiconductors though an inkjet printing process. This enabled us to deposit functional polymers with a high degree of alignment and explore its use in polarization sensitive OPDs. Secondly, I will outline our recent efforts in the fabrication of inkjet printed OPDs based on novel non-fullerene acceptors (NFAs). The devices show a photo-response up to 800nm and reach record responsivities of 400mA/W as well as cut-off frequencies surpassing 2MHz. Furthermore, we demonstrate the successful decoupling of the optical and rheological properties by using a visibly transparent polymer donor and color-selective NFAs. This approach offers spectral flexibility without the need for a variation in process parameters. The choice of NFA enabled devices with color selectivity in the ranges of 400-600nm and 500-800nm enabling a proof of concept filterless visible-light communication system. Finally, I will present the fabrication printed passive and active matrix OPD arrays.

Photodetectors that are sensitive in shortwave infrared (SWIR) range (1 µm - 2 µm) are of significant interest for applications in 3D, night and adverse weather imaging, machine vision, autonomous driving, among others. Currently available technologies in the SWIR rely on costly epitaxial semiconductors that are not monolithically integrated with CMOS electronics. Solution-processed quantum dots have been developed to address this challenge enabling low-cost manufacturing and facile monolithic integration on silicon in a back-end-of-line (BEOL) process. To date, colloidal quantum dot (CQD) materials to access the SWIR have been based on lead sulfide (PbS) and mercury telluride (HgTe) compounds imposing major regulatory concerns and potentially impeding their deployment in consumer electronics. In this talk I will present a novel synthetic method of environmentally friendly silver telluride quantum dots and their application in high-performance SWIR photodetectors. The CQD photodetector stack is entirely based on Restriction of Hazardous Substance (RoHS) compliant materials and exhibits a spectral range from 350 nm - 1600 nm, with room-temperature detectivity of the order 10¹² Jones, 3dB bandwidth in excess of 100 KHz and linear dynamic range of over 118 dB. We further demonstrate, for the first time, a monolithically integrated SWIR imager that is based on solution processed, heavy-metal-free materials, paving the way of this technology to consumer electronics market [1]. In the second part of the talk I will turn to our recent activities on the development of III-V CQDs and their applicaiton in photodetectors aiming for speeds suited for gated imaging. I will dicuss the challenges on the synthesis of InSb CQDs in terms of surface passivation and environmental stability and present our approach to overcome those challenges reporting InSb CQD SWIR photodetector that exhibits external quantum efficiency (EQE) of 25% at 1240 nm, a wide linear dynamic range exceeding 128 dB, fast photoresponse time of 70 ns, and specific detectivity of 3.6 × 10¹² Jones.

[1] Silver Telluride Colloidal Quantum Dot Infrared Photodetectors and Image Sensors, Yongjie Wang¹, Lucheng Peng¹, Julien Schreier², Yu Bi², Andres Black², Aditya Malla¹, Stijn Goosens², Gerasimos Konstantatos^1,3*, Nature Photonics, accepted.

The ultraviolet (UV) part of spectrum is of paramount importance for a large range of applications from health and safety to process and environmental monitoring. Yet the complexity of integrating UV sensitive optoelectronics on standard complementary metal–oxide–semiconductor (CMOS) technology has curtailed to a large extent the use of UV spectrum, especially in consumer electronics. Currently UV photodetectors rely on III-V nitride semiconductors that are not monolithic to silicon and are typically fabricated off-die.

    We overcome this challenge by developing RoHS compliant environmentally friendly colloidal quantum dots (QDs) (zinc magnesium oxide , ZnMgO) which has compositionally tunable absorption across UV and high photoluminescence quantum yield (> 90%) in the visible.[1] Herein, we will present a non-toxic, visible blind QD based down-converting thin-film technology that expands the spectral coverage of Si-CMOS-sensors into the UV, enabling efficient UV detection without affecting the sensor performance in the visible and NIR. A Si-photodetector (PD) integrated with the QDs results in a record 9-fold improvement (800% relative enhancement) in photoresponsivity from 0.83 to 7.5 mA W⁻¹ at 260 nm. Leveraging the tunability of these QDs, we will show a simple UV-band identification scheme (a sensor), which uses two distinct-bandgap ZnMgO QDs stacked in a tandem architecture whose spectral emission color depends on the UV-band excitation light. The downconverting stack enables facile discrimination of UV light (different UV bands) using a standard CMOS image sensor (camera) or by the naked eye and avoids the use of complex optics.

 Colloidal infrared (IR) quantum dots (QDs) have been studied with many advantages, such as tunable absorption and fluorescence emission spectra, high molar extinction coefficients, high photoluminescence (PL) quantum yield, high stability, cost-efficient and scalable synthesis, and solution processability. Most of the reported IR-active QDs are based on materials containing toxic heavy metals, such as PbS and HgTe QDs. III- V semiconductors containing one group-13 and one group-15 element of the periodic table are highly promising Pb- and Hg-free alternative materials.^[1] Colloidal InSb QDs have been considered as a low-toxic alternative to Pb or Hg chalcogenide QDs. The InSb has a large excitonic Bohr radius of ~60 nm, and it allows the band gap of InSb QDs to be widely tuned in the IR spectral range through size control. However, only a few chemical synthesis methods have been reported due to the limited precursors and the synthesized InSb QDs have featureless or broad excitonic absorption peaks showing extremely broad size distribution so far.

 Here, we report the chemical synthesis and surface engineering of colloidal InSb QDs. In the synthesis part, various synthesis parameters such as precursors, temperature, time, and an introduction of additional ions are explored to produce InSb QDs with unprecedented optical quality. The optical properties of InSb QDs are studied mainly based on the wavelength and the width of the excitonic absorption features. We demonstrate full tunability of the first excitonic absorption peak in the IR range from 700 to 2000 nm and narrow line widths by virtue of an improved size homogeneity of the InSb QDs. The effect of each synthesis parameter on the optical properties of InSb QDs and their growth mechanism will be discussed. In the surface engineering part, the surface ligands of InSb QDs are altered from the original long-chain organic ligands to short-chain ligands to afford conductive InSb QDs films. Several ligands were tested and their optical/structural properties of InSb QDs were compared before and after surface modification. With the thus optimized experimental conditions, we obtain InSb QDs films with high stability, high conductivity, and suitable band energy levels for application as environmentally benign IR photodetectors.

Photodetectors on the basis of transition metal dichalcogenides (TMDCs) have let to impressive performance numbers with regard to gain and responsivity.¹ In contrast, their speed, parametrized by the response time and 3dB electrical bandwidth, has been mostly disappointing so far with response times often ranging in the milli- to microsecond regimes. The corresponding 3dB bandwidths seldomly exceed a few MHz, and this is too slow to be competitive with established, fast photodetection materials that typically operate with GHz speed.

This presentation details how rational tuning of the substrate material,² the contact geometry,³ the photoresistance and the capacitance⁴ of lateral photodetectors based on mechanically exfoliated WSe₂ layers affects the 3dB bandwidth and enables photodetection with a speed in excess of 230 MHz. We show that optical switching with such devices can be carried out at zero bias, requiring just 27 fJ per switching event. Reducing the detector thickness to mono- and bilayers of WSe₂ only weakly decreases the response speed, rendering WSe₂ advantageous over MoS₂ for fast optical communication. Further miniaturizations of the device geometry have the potential for Gigahertz photodetection with such easily fabricated TMDC photodetectors which exhibit long-term stability under ambient conditions.

Organic semiconductors have raised much attention due to their many attractive properties, like low-cost, light weight, mechanical flexibility, and abundant availability. Despite that, they still lack high mobility compared to their inorganic counterparts as a consequence of their often amorphous nature.
An exception to this is rubrene, which can form highly ordered phases, demonstrating an extraordinarily high charge carrier mobility for holes (>10 cm²/(Vs)^-1) even in thin films. Depending on the post-treatment of our vacuum-deposited films, we can control different crystalline phases, like the orthorhombic and triclinic ones.
For fast-response OPDs, the triclinic phase is a promising candidate since it exhibits high hole mobility in the vertical direction. However, the high surface roughness is a crucial reason why these devices fall short in specific detectivity up to now. In this work, we employ different strategies to reduce the impact of Ohmic shunts within the device to minimize the noise current of our devices. Optimizing the concentration of rubrene and C₆₀ in the active layer and adjusting the electron transport material and its thickness are essential building blocks for achieving low noise currents. However, the most promising approach has been to establish a suppressing layer for the post-treatment of the film. This suppressing layer allows to reduce the dark current by four orders of magnitude. We characterize the morphology of our films with atomic force microscopy and grazing-incidence wide-angle X-ray scattering and investigate the performance parameters of fully working devices. In addition to a low noise current, a high external quantum efficiency is crucial for achieving high specific detectivity values. We can accomplish a competitive specific detectivity of 10¹³ with the employed strategies based on thermal noise domination at 0 V. Speed, noise, and linear dynamic range are investigated to complement the study.

Metal halide perovskites (MHPs) have shown excellent results as X-ray scintillation detectors. X-ray tomography requires many projections and therefore scintillators with excellent stability, which is challenging for MHPs that often suffer from fast degradation under X-ray irradiation and ambient conditions. MHP nanowires could offer improved sensitivity and resolution by exploiting nanophotonic light guiding, and the stability could be improved by growing physically protected nanowires directly in anodized aluminum oxide (AAO) nanopore templates.

We have developed a one-step solution method to grow arrays of up to 30 μm long single-crystalline CsPbBr₃ nanowires in an AAO template, with controlled diameters ranging from 30 to 360 nm [1,2]. The CsPbBr3 nanowires in AAO (CsPbBr3 NW/AAO) show increasing X-ray scintillation efficiency with decreasing nanowire diameter, with a maximum photon yield of ∼5 300 ph/MeV at 30 nm diameter. 2D X-ray images can distinguish line pairs with a spacing of 2 μm and slanted edge measurements show a spatial resolution of ∼160 lp/mm at modulation transfer function (MTF) = 0.1 [1]. The stability was tested over 2 weeks of X-ray exposure [3]. The X-ray scintillation unexpectedly correlated positively with room humidity, but showed no systematic degradation. The resolution was stable at (180 ± 20) , i.e., about 2.8 micron.

For 3D microscopy, a tomogram with 600 projections was taken with a Cu X-ray source over 41 h. The scintillation variations remained below 5% during the acquisition, which allowed a successful 3D reconstruction with high spatial resolution [3]. The combination of high spatial resolution, radiation stability, and easy fabrication makes these CsPbBr3 NW/AAO scintillators a promising candidate for high-resolution X-ray imaging applications.

The development of detectors for high energy photons, protons and heavy particles is a long-lasting research topic not only for fundamental applications but also, more recently, for medical applications in radio and hadron therapy. There is an increasing demand for sensors able to provide, ideally in-situ and in real-time, an accurate recording and mapping of the dose delivered during a treatment plan. The development of novel high performing, thin and flexible sensors for the detection of ionizing radiation in real-time at affordable costs is rapidly increasing, as the technology currently available still fails to address the requirements of large-area, conformability and portability, lightweight and low power operation.

Organic small molecules and polymers are promising active layers for advanced dosimetry purposes, as their mechanical features allow the development of devices able to adapt to complex contoured surfaces with outstanding portability (low power operation) and lightweight. They also provide the unique possibility to develop human-tissue-equivalent detectors, thanks to their density and composition, which makes them ideal candidates for medical dosimetry applications. Their low average atomic number and density, also grants a low absorption of the incoming radiation, making them extremely radiation-tolerant. The physical process of radiation detection for organic thin- film based detectors will be discussed in two different configurations: 1) the direct one, based on a simple planar device with an organic thin film as active conversion layer, and 2) the indirect one, based on a polysiloxane-based scintillating layer effectively coupled to an organic phototransistor (OPT).

We report on their performance under exposure to intense photons and MeV protons radiation fields and will discuss how to detect and exploit the energy absorbed both by the organic semiconducting layer and by the plastic substrate, allowing to extrapolate information on the irradiation history of the detector. A new kinetic model has been developed to describe the detector response mechanism, able to precisely reproduce the dynamic response of the device under photon/proton irradiation and to provide further insight into the physical processes controlling its response.

Organic semiconductors have proven to be a versatile technology platform and are compatible with high-scale mass production. Vacuum-deposited organic light-emitting diodes (OLEDs) dominate mobile display applications and are superior due to their mechanical flexibility, high contrast, low-cost, and form-free production. Recently, organic photodetectors have attracted much interest since they are directly compatible with the OLED display technology and have excellent potential to complement it. Furthermore, their physical properties, such as semitransparency, flexibility, narrowband detection, and, most importantly, high detectivity, offer new perspectives for optoelectronic sensing and will stimulate new consumer electronics applications.

Typically, organic solar cells and photodetectors are comprised of an electron donating and accepting material to facilitate efficient charge carrier generation. This approach has proven successful in achieving high-performance devices but has several drawbacks. For example, creating the proper donor-acceptor microstructure is critical to achieve the desired performance. However, this is challenging when it comes to upscaling and is considered one of the significant degradation pathways regarding the stability of these devices. Therefore, we investigate a vacuum-deposited oligothiophene A-D-A molecule in a single-component device and find that it can generate free charge carriers with an internal quantum efficiency of 20% already at zero bias. Optimizing the device structure, we achieve specific detectivities of 10¹³ Jones (based on noise measurements), high speed (f_-3dB = 330 kHz), and linear dynamic range (190 dB). To unveil the charge carrier generation within this material system, we employ ultrafast transient absorption spectroscopy and quantum chemical calculations and find that free charge carriers are already formed at time scales below one picosecond. Exhibiting this excellent performance and using the simple device structure, such single-component devices are perfect candidates for application.

Methylammonium lead bromide (MAPbBr₃) have emerged as the next-generation materials for self-powered photodetectors due to its easy fabrication protocol and better stability. However, there is still a lack of sufficient understanding of the effect of electrode distance, metal contacts, irradiation power and applied temperature on the performance of MAPbBr₃ SC-based perovskite PDs. Here, we demonstrated the impact of different electrode materials, variable electrode distance,¹ light intensities and temperatures on the performance of MAPbBr₃ SC-based perovskite PDs and analyse them with the help of transient photoresponse and impedance spectroscopy.² This study reveals that the key performance parameters of PD decrease with increasing irradiation intensity as well as increase in Schottky barrier height (SBH) between the metal and the semiconductor, due to changes in charge recombination and carrier lifetime.^2,3 On the other hand, the temperature-dependent study revealed that the performance of PD was found to be related to the increasing scattering of impurities, temperature activated ion accumulation, and phonons, change in conductivity and band gap rather than the change in charge recombination. Next, we fabricated a planar-type PD based on metal doped p-type MAPbBr₃/n-type MAPbBr₃ SC junction photodiode using asymmetric electrode and use the combined effect of electric field due to asymmetric Schottky barrier formation and additional built-in electric field in the p-n junction depletion region demonstrate for the first time to achieve excellent self-powered photodetection properties.⁴ The p-n junction on the MAPbBr₃ single crystal was formed by a controlled epitaxial grow of Ag⁺ doped MAPbBr₃ SC (p-type) on the facet of Sb³⁺ doped MAPbBr₃ SC (n-type). The as-integrated p-n junction device with asymmetric electrodes shows a typical photovoltaic behaviour with a high open circuit voltage of 0.95 V and great sensitivity to 530 nm illumination at zero bias with a responsivity of up to 0.41 A W^-1 and a specific detectivity of 6.39 × 10¹¹ Jones, which are among the highest values reported for MAPbBr₃ single crystal based self-powered photodetectors. In addition, the p-n junction device maintained 80% of the initial performance after being exposed under continuous operation illumination for 12 h in atmospheric condition and restored 94% performance of its initial value after 36 h of storage in the dark. This work provides a new way for designing a high performance self-powered perovskite-based p-n junction photodiodes.

The rapid development of industry in field of machine vision systems, the Internet of Things (IoT) and smart houses rises the demand for scalable bifacial photodetectors [1-3]. Perovskite photodetectors (PPDs) hold a great potential to dominate photodetector market due to their high detectivity, fast response, and cost-effectiveness. However, unlocking the full potential of PPDs for the industry requires overcoming critical technological challenges, notably in scalability, robustness, weight, and semitransparency.

To bring PPDs towards commercialization, we have fabricated scalable self-powered PPDs using the industrially compatible slot-die coating technique on flexible plastic substrates. The integration of thin dielectric-metal-dielectric layers as transparent top contacts has granted the devices with an impressive bifaciality factor of 78% and light-to-dark current ratios reaching an order of magnitude of 10⁴. Alongside their high detectivity, fabricated PPDs possess the capability to harness solar energy, exhibiting reasonable power conversion efficiencies (PCEs) from both, the bottom- and top-side illuminations.

In this presentation, we will showcase the advancements we made in scalable PPD technology. We will discuss the role of selection of top contacts to optimize the performance of bifacial optoelectronics and conclude the key aspects of fabrication of scalable devices.

The very rapid growth of internet-connected devices brings two important challenges.  The first is how will all these devices communicate?  The second is how will they be powered? Optical communications can help, particularly in the form of “Li-Fi” which modulates indoor lighting to transmit information.  It is important to supplement Wi-Fi because the radio frequency spectrum is now very crowded.  Organic semiconductors have been shown to be useful as both transmitters and receivers for Li-Fi, and also for indoor power harvesting.

This talk will give an overview of Li-Fi using organic semiconductors and then focus on their use as receivers.   In particular it will show how organic photovoltaics can be used to receive data and generate power simultaneously.   By using an array  of four detectors in a multiple input multiple -output (MIMO) setup data rates up to 363 megabits per second were achieved together with simultaneous harvesting of power.  These results show that organic photovoltaics can be used for wireless data communication while prolonging the battery life of a mobile device.