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.

We show that crystallographic compatibility, quantum yield, and fatigue resistance are three important factors that diarylethene (DAE) should simultaneously satisfy to realize high-performance photoprogrammable polymer field-effect transistors (FETs). The enhancement of crystallographic compatibility achieved by locating DAE preferentially in the vicinity of intercrystallite tie chains is mainly dependent on the overall molecular volume of DAE. The quantum yield of DAE for photocyclization is dependent on the molar portion of the photoactive antiparallel conformer, while photocycloreversion is determined by both the aromatic stabilization energy of the closed isomer and allowed free space for each DAE molecule. While the chemical resistance of DAE relies entirely on its chemical structure, the electrical fatigue resistance of DAE-embedded FET depends on both the morphological/structural environment of the DAE/polymer blend and chemical resistance of the DAE molecule. To precisely control each of these determining factors of DAE-embedded polymer FETs, a series of DAE is synthesized and systematically analyzed. High-mobility DPPDTT is blended with various DAE derivatives as a matrix polymer. We show that strategic substitution of functional groups at the specific reaction site of DAE can lead to an ideal molecular switch for high-performance photoprogrammable polymer FETs with high photoprogrammable switching ratios of 4405, as well as high electrical fatigue resistance of up to 100 photoprogrammable switching steps. The physics behind the success of the optimized DAE structure is discussed using the results from various analysis techniques. We shed light on how the crystallographic compatibility, quantum yield, and fatigue resistance of DAE can vary with and be optimized by chemical modification of the DAE reaction site.

A fully water-based patterning method for polymer semiconductors was developed and utilized to realize high-precision lateral patterning of various polymers. Water-borne polymer colloids, wherein hydrophobic polymers are dispersed in water with the assistance of surfactant molecules, possess a hydrophilic surface when printed onto a substrate. When this surface is exposed to a washing molecule, the surface of the polymer film recovers its original hydrophobic nature. Such surfactant-induced solubility control (SISC) enables environmentally benign, water-processed, and high-precision patterning of various polymer semiconductors with totally different solubilities, so that fully water-processed polymer organic image sensors (OISs) can be realized. B-/G-/R-selective photodiodes with a pixel size of 100 μm × 100 μm were fabricated and patterned by this water-based SISC method, leading to not only high average specific detectivity values (over 1012 Jones) but also narrow pixel-to-pixel deviation. Thanks to the superiority of the SISC method, we demonstrate the image capturing ability of OISs without B-/G-/R-color filters, from a fully water-based fabrication process.

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