High-Detectivity All-Polymer Photodetectors with Spectral Response from 300 to 1100 nm

Design of Ultra-Narrow Bandgap Polymer Acceptors for High-Sensitivity Flexible All-Polymer Short-Wavelength Infrared Photodetectors

All-polymer photodetectors possess unique mechanical flexibility and are ideally suitable for the application in next-generation flexible, wearable short-wavelength infrared (SWIR, 1000-2700 nm) photodetectors. However, all-polymer photodetectors commonly suffer from low sensitivity, high noise, and low photoresponse speed in the SWIR region, which significantly diminish their application potential in wearable electronics. Herein, two polymer acceptors with absorption beyond 1000 nm, namely P4TOC-DCBT and P4TOC-DCBSe, were designed and synthesized. The two polymers possess rigid structure and good conformational stability, which is beneficial for reducing energetic disorder and suppressing dark current. Owing to the efficient charge generation and ultralow noise current, the P4TOC-DCBT-based all-polymer photodetector achieved a specific detectivity (D * ${{D}^{^{\ast}}}$ ) of over 1012 Jones from 650 (visible) to 1070 nm (SWIR) under zero bias, with a response time of 1.36 μs. These are the best results for reported all-polymer SWIR photodetectors in photovoltaic mode. More significantly, the all-polymer blend films exhibit good mechanical durability, and hence the P4TOC-DCBT-based flexible all-polymer photodetectors show a small performance attenuation (<4 %) after 2000 cycles of bending to a 3 mm radius. The all-polymer flexible SWIR organic photodetectors are successfully applied in pulse signal detection, optical communication and image capture.

High-Detectivity All-Polymer Photodiode Empowers Smart Vitality Surveillance and Computational Imaging Rivaling Silicon Diodes

Near-infrared (NIR) organic photodetectors (OPDs), particularly all-polymer-based ones, hold substantial commercial promise in the healthcare and imaging sectors. However, the process of optimizing their active layer composition to achieve highly competitive figures of merit lacks a clear direction and methodology. In this work, celebrity polymer acceptor PY-IT into a more NIR absorbing host system PBDB-T:PZF-V, to significantly enhance the photodetection competence, is introduced. The refined all-polymer ternary broadband photodetector demonstrates superior performance metrics, including experimentally measured noise current as low as 6 fA Hz-1/2, specific detectivity reaching 8 × 1012 Jones, linear dynamic range (LDR) of 145 dB, and swift response speed surpassing 200 kHz, striking a fair balance between sensitivity and response speed. Comprehensive morphological and photophysical characterizations elucidate the mechanisms behind the observed performance enhancements in this study, which include reduced trap density, enhanced charge transport, diminished charge recombination, and balanced electron/hole mobilities. Moreover, the practical deployment potential of the proof-of-concept device in self-powered mode is demonstrated through their application in a machine learning-based cuffless blood pressure (BP) estimation system and in high-resolution computational imaging across complex environments, where they are found to quantitatively rival commercial silicon diodes.

Organic Photodetectors with Extended Spectral Response Range Assisted by Plasmonic Hot-Electron Injection

Organic photodetectors (OPDs) have aroused intensive attention for signal detection in industrial and scientific applications due to their advantages including low cost, mechanical flexibility, and large-area fabrication. As one of the most common organic light-emitting materials, 8-hydroxyquinolinato aluminum (Alq3) has an absorption wavelength edge of 460 nm. Here, through the introduction of Ag nanoparticles (Ag NPs), the spectral response range of the Alq3-based OPD was successfully extended to the near-infrared range. It was found that introducing Ag NPs can induce rich plasmonic resonances, generating plenty of hot electrons, which could be injected into Alq3 and then be collected. Moreover, as a by-product of introducing Ag NPs, the dark current was suppressed by around two orders of magnitude by forming a Schottky junction on the cathode side. These two effects in combination produced photoelectric signals with significant contrasts at wavelengths beyond the Alq3 absorption band. It was found that the OPD with Ag NPs can stably generate electric signals under illumination by pulsed 850 nm LED, while the output of the reference device included no signal. Our work contributes to the development of low-cost, broadband OPDs for applications in flexible electronics, bio-imaging sensors, etc.

High-Performance Photodetectors Based on Nanostructured Perovskites

In recent years, high-performance photodetectors have attracted wide attention because of their important applications including imaging, spectroscopy, fiber-optic communications, remote control, chemical/biological sensing and so on. Nanostructured perovskites are extremely suitable for detective applications with their long carrier lifetime, high carrier mobility, facile synthesis, and beneficial to device miniaturization. Because the structure of the device and the dimension of nanostructured perovskite have a profound impact on the performance of photodetector, we divide nanostructured perovskite into 2D, 1D, and 0D, and review their applications in photodetector (including photoconductor, phototransistor, and photodiode), respectively. The devices exhibit high performance with high photoresponsivity, large external quantum efficiency (EQE), large gain, high detectivity, and fast response time. The intriguing properties suggest that nanostructured perovskites have a great potential in photodetection.

High-Performance All-Polymer Photodetectors via a Thick Photoactive Layer Strategy

To achieve high detectivity in all-polymer photodetectors (all-PPDs), a thick-film photoactive layer is favored because it can effectively suppress the dark current density. However, if the photoactive layer of the film is too thick, it leads to reduced responsivity owing to increased recombination loss. We developed high-performance all-PPDs by using a narrowband-gap p-type polymer NT40 and an n-type polymer poly{[ N, N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]- alt-5,5'-(2,2'bithiophene)} as the photoactive layer. The high charge carrier mobility of both copolymers enabled a photoactive layer thickness of 300 nm, leading to an ultralow dark current density of 4.85 × 10^-10 A cm^-2, a detectivity of 2.61 × 10¹³ Jones, a high responsivity of 0.33 A W^-1 at 720 nm, and a bias of -0.1 V. The detectivity achieved >10¹³ Jones in a wide range from 360 to 850 nm, which is among the highest values so far reported for all-PPDs without extra gains. More importantly, the resultant all-PPDs exhibited a high working frequency over 10 kHz associated with a large linear dynamic range. These findings demonstrate great potential for practical applications of the all-PPDs developed in this work.

Dark Current Reduction Strategy via a Layer-By-Layer Solution Process for a High-Performance All-Polymer Photodetector

The ideal bulk-heterojunction for high-performance organic photodetectors prefers a morphology with a vertically gradient component to suppress the leaking current. Here, we demonstrate an all-polymer photodetector with a segregated bulk-heterojunction active layer. This all-polymer photodetector exhibits a dramatically reduced dark current density because of its built-in charge blocking layer, with a responsivity of 0.25 A W^-1 at a wavelength of approximately 600 nm and specific detectivity of 5.68 × 10¹² cm Hz^1/2 W^-1 as calculated from the noise spectra at 1 kHz. To our knowledge, this is among the best performances reported for photodetectors based on both polymeric donor and acceptor in the photoactive layer. These findings present a facile approach to improving the specific detectivity of polymer photodetectors via a layer-by-layer solution process.

High Performance All-Polymer Photodetector Comprising a Donor-Acceptor-Acceptor Structured Indacenodithiophene-Bithieno[3,4-c]Pyrroletetrone Copolymer

The synthesis of an acceptor polymer PIDT-2TPD, comprising indacenodithiophene (IDT) as the electron-rich unit and an interconnected bithieno[3,4-c]pyrrole-4,4',6,6'-tetrone (2TPD) as the electron-deficient unit, and its application for all-polymer photodetectors is reported. The optical, electrochemical, charge transport, and device properties of a blend of poly(3-hexylthiophene) and PIDT-2TPD are studied. The blend shows strong complementary absorption and balanced electron and hole mobility, which are desired properties for a photoactive layer. The device exhibits dark current density in the order of 10^-5 mA/cm², external quantum efficiency broadly above 30%, and nearly planar detectivity over the entire visible spectral range (maximum of 1.1 × 10¹² Jones at 610 nm) under -5 V bias. These results indicate that PIDT-2TPD is a highly functional new type of acceptor and further motivate the use of 2TPD as a building block for other n-type materials.

Side-chain engineering in naphthalenediimide-based n-type polymers for high-performance all-polymer photodetectors

Optimization of the all-polymer photodetector performance by tuning the size of side chains in NDI-based acceptor polymers.