A photomultiplication-type organic photodiode (PM-OPD), where an electric double layer (EDL) is strategically embedded, is demonstrated, with an exceptionally high external quantum efficiency (EQE) of 2 210 000%, responsivity of 11 200 A W −1 , specific detectivity of 2.11 × 10 14 Jones, and gain-bandwidth product of 1.92 × 10 7 Hz, as well as high reproducibility. A polymer electrolyte, poly(9,9-bis(3′-(N,N-dimethyl)-N-ethylammoinium-propyl-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene))dibromide is employed as a work-function-modifying layer of indium tin oxide (ITO) to construct an EDL-embedded Schottky junction with p-type polymer semiconductor, poly(3-hexylthiophene-diyl), resulting in not only advantageous tuning of the work function of ITO but also an enhancement of the electron-trapping efficiency due to electrostatic interaction between exposed cations and trapped electrons within isolated acceptor domains. The effects of the EDL on the energetics of the trapped electron states and thus on the gain generation mechanism are confirmed by numerical simulations based on the drift-diffusion approximation of charge carriers. The feasibility of the fabricated high-EQE PM-OPD especially for weak light detection is demonstrated via a pixelated prototype image sensor. It is believed that this new OPD platform opens up the possibility for the ultrahigh-sensitivity organic image sensors, while maintaining the advantageous properties of organics.

A high gain-bandwidth product of photomultiplication-type organic photodiode is limited. We show that newly designed regioregular polymer enables a highly oriented face-on structure with a low trap density, leading to...

When the intensity of the incident light increases, the photocurrents of organic photodiodes (OPDs) exhibit relatively early saturation, due to which OPDs cannot easily detect objects against strong backlights, such as sunlight. In this study, this problem is addressed by introducing a light‐intensity‐dependent transition of the operation mode, such that the operation mode of the OPD autonomously changes to overcome early photocurrent saturation as the incident light intensity passes the threshold intensity. The photoactive layer is doped with a strategically designed and synthesized molecular switch, 1,2‐bis‐(2‐methyl‐5‐(4‐cyanobiphenyl)‐3‐thienyl)tetrafluorobenzene (DAB). The proposed OPD exhibits a typical OPD performance with an external quantum efficiency (EQE) of <100% and a photomultiplication behavior with an EQE of >100% under low‐intensity and high‐intensity light illuminations, respectively, thereby resulting in an extension of the photoresponse linearity to a light intensity of 434 mW cm−2. This unique and reversible transition of the operation mode can be explained by the unbalanced quantum yield of photocyclization/photocycloreversion of the molecular switch. The details of the operation mechanism are discussed in conjunction with various photophysical analyses. Furthermore, they establish a prototype image sensor with an array of molecular‐switch‐embedded OPD pixels to demonstrate their extremely high sensitivity against strong light illumination.

Herein, we explore the strategy of realizing a red-selective thin-film organic photodiode (OPD) by synthesizing a new copolymer with a highly selective red-absorption feature. PCZ-Th-DPP, with phenanthrocarbazole (PCZ) and diketopyrrolopyrrole (DPP) as donor and acceptor units, respectively, was strategically designed/synthesized based on a time-dependent density functional theory calculation, which predicted the significant suppression of the band II absorption of PCZ-Th-DPP due to the extremely efficient intramolecular charge transfer. We demonstrate that the synthesized PCZ-Th-DPP exhibits not only a high absorption coefficient within the red-selective band I region, as theoretically predicted, but also a preferential face-on intermolecular structure in the thin-film state, which is beneficial for vertical charge extraction as an outcome of a glancing incidence X-ray diffraction study. By employing PCZ-Th-DPP as a photoactive layer of Schottky OPD, to fully match its absorption characteristic to the spectral response of the red-selective OPD, we demonstrate a genuine red-selective specific detectivity in the order of 1012 Jones while maintaining a thin active layer thickness of ∼300 nm. This work demonstrates the possibility of realizing a full color image sensor with a synthetic approach to the constituting active layers without optical manipulation.

A facile and strategic junction tuning technology is reported to boost self-powered organic Schottky photodiode (OPD) performances by synergetic contributions of reactive dedoping effects. It is shown that dedoping poly­(3-hexylthiophene-2,5-diyl) (P3HT) films with 1-propylamine (PA) solution significantly reduces not only acceptor-defect density but also intrinsic doping level, leading to dramatically enlarged depletion width of metal/polymer Schottky junctions, as confirmed by ultraviolet photoelectron spectroscopy and Mott–Schottky junction analyses. As a result, whole penetration regions of photons corresponding to absorption bands of P3HT can be fully covered by the depletion region of Schottky junctions, even without the assistance of external electric fields. In addition, it is shown that non-solvent exposure effects of PA dedoping further enable lower paracrystalline disorder and, thus, higher charge carrier mobility, by means of grazing incidence X-ray diffraction, field-effect mobility, and space-charge-limited current analyses. As a result of such synergetic advantages of the PA dedoping method, non-power-driven green-selective OPDs were demonstrated with a high specific detectivity exceeding 6 × 1012 Jones and a low noise-equivalent power of 5.05 × 10–14 W Hz–0.5. Together with a fast temporal response of 26.9 μs and a wide linear dynamic range of 201 dB, the possibility of realizing non-power-driven, near-ideal optimization of solution-processed OPDs with a facile dedoping method is demonstrated.

A synthetic approach for engineering an electric double layer (EDL)–photoactive layer interface in photomultiplication-type organic photodetectors (PM-OPD), whereby the EDL is strategically embedded between a transparent cathode and the photoactive...

Precise and facile junction engineering of organic photodiodes (OPDs) via chemical doping is demonstrated.

In this study, it is shown that fluorinated azide, employed as a functional additive to photomultiplication-type organic photodiodes (PM-OPDs), can not only enhance an operational stability by freezing the morphology...