A Molecular‐Switch‐Embedded Organic Photodiode for Capturing Images against Strong Backlight

Abstract

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.

Ultralow-voltage operation of light-emitting diodes

“…To gain further insight, we employ a widely used device simulation software “Setfos” 50 , 51 to model the emission behaviour of LEDs. We constructed model devices including a lead-iodide perovskite LED, and a standard phosphorescent OLED based on Ir(ppy) 3 (Fig.…”

“…In addition to the LED modelling and EL intensity-voltage data fitting presented in this work, we carried out device simulations for a lead-iodide perovskite LED and a Ir(ppy) 3 OLED using a LED simulation software “Setfos” 50 , 51 . The preset parameters for these devices are available from the database of the device simulation package, with detailed settings and modifications presented in Supplementary Tables 3 and 4 .…”

Stoichiometric Engineering of Cs2AgBiBr6 for Photomultiplication-Type Photodetectors

“…So far, studies on PM-PDs have been mainly conducted with organic semiconductors because trap states can be efficiently engineered by adjusting the ratio of p-type and n-type semiconductors by using both solution , and vacuum deposition processes. , In PM-type organic PDs (PM-OPDs), the PM mechanism is explained based on the trap-assisted charge injection model; i.e., the photogenerated charge carriers trapped near the electrode induce band banding at the semiconductor/electrode interface, resulting in injections of multiple charge carriers. In the case of PM-OPDs, a small number of trap molecules (e.g., n-type semiconductors) are mixed with a major component (e.g., p-type semiconductors) to generate spatially isolated electron trap states. − Consequently, the exciton dissociation yield cannot be as high as that of typical organic bulk-heterojunctions due to the limited p–n interfacial area. On the other hand, organic–inorganic methylammonium (MA) and formamidinium (FA) lead halide perovskite (hybrid perovskite) with strong optical absorption on the order of 10 5 cm –1 , low exciton binding energy, long diffusion lengths (>1 μm), and high photoluminescence quantum yield (PLQY) can be regarded as a promising alternative for low-voltage operating PM-PDs, once efficient trap engineering is realized.…”

Optimizing ionic strength of interfacial electric double layer for ultrahigh external quantum efficiency of photomultiplication-type organic photodetectors

“…With regard to PM-OPDs, the key to achieving high gain values is achieving continuous charge injection from the cathode to the semiconductor via an unfavourable Schottky barrier; this can be achieved via Schottky barrier thinning driven by a localized electric field generated by trapped electrons. 5,6,18 In this regard, the deeper electron trapping energy of the MP6-Br − -based PM-OPD is believed to be optimal for efficient gain generation.…”

“…In this regard, organic photodetectors, which employ organic semiconductors as the photoactive layer, are considered a suitable alternative to Si-based photodetectors, owing to their direct energy bandgap and facile band structure control through molecular design. 2–16 In particular, photomultiplication-type organic photodetectors (PM-OPDs) have garnered significant attention for the detection of weak light signals, owing to their self-amplifying characteristics; notably, PM-OPDs have achieved an extremely high external quantum efficiency (EQE) of over 10 000%. This high EQE of PM-OPDs is attributed to the photoconductive gain generation.…”