On the Response Speed of Narrowband Organic Optical Upconversion Devices

Abstract

and are still cost prohibitive for most consumer and low-end applications. In addition, due to the broadband absorption of inorganic semiconductors, spectrally selective detection is not possible without attached optical filters.As an alternative approach, optical upconversion devices have been developed that directly convert NIR light into visible light. These devices are also denoted as upconversion photodetector, [9] upconversion display/imager, [10,11] or upconversion light-emitting diode. [12] The basic idea of any upconverter is the serial connection of a NIR photodetector with a visible lightemitting component. When NIR light is absorbed in the photodetector, a current is generated and directly converted into a visible image by the emitter element. Important advantages of this design concept are that no intermediate electronics for data processing and no external display for data visualization are required. We note that the functionality of an upconverter is different from the several known photon upconversion processes. Photon upconversion is a process that converts sequentially absorbed photons of low energy into a photon of higher energy.All-organic upconversion devices (OUCs) are composed of an organic NIR photodetector and an organic light-emitting diode (OLED). OUCs can be fabricated entirely from solution over large area using coating and printing processes. This potentially enables new and alternative NIR imaging applications Organic upconversion devices (OUCs) consist of an organic infrared photodetector and an organic visible light-emitting diode (OLED), connected in series. OUCs convert photons from the infrared to the visible and are of use in applications such as process control or imaging. Many applications require a fast OUC response speed, namely the ability to accurately detect in the visible a rapidly changing infrared signal. Here, high image-contrast, narrowband OUCs are reported that convert near-infrared (NIR) light at 980 and 976 nm with a full-width at half maximum of 130 nm into visible light. Transient photocurrent measurements show that the response speed decreases when lowering the NIR light intensity. This is contrary to conventional organic photodetectors that show the opposite speed-versus-light trend. It is further found that the response speed increases (when using a phosphorescent OLED) or decreases (for a fluorescent OLED) when increasing the driving voltage. To understand these surprising results, an analysis by numerical simulation is conducted. Results show that the response speed behavior is primarily determined by the electron mobility in the OLED. It is proposed that the low electron drift velocity in the emitter layer sets a fundamental limit to the response speed of OUCs.

Transparent organic upconversion devices displaying high-resolution, single-pixel, low-power infrared images perceived by human vision

“…For example, Hu et al. ( 44 ) recently demonstrated a η p-p of 0.16% with an EQE product of 0.29% from the OPD (10%) and OLED (2.89%) subunits. Yang et al.…”

“…The upconversion performance can be estimated by the EQE product of the infrared photodetector and the LED, respectively, or as a whole (43). For example, Hu et al (44) recently demonstrated a η p-p of 0.16% with an EQE product of 0.29% from the OPD (10%) and OLED (2.89%) subunits. Yang et al (12) achieved a record-high η p-p of 29.6% with an EQE of 61.7% from the CGL and an ultrahigh EQE of 50% from the tandem OLED.…”

Infrared Light Detection Technology Based on Organics

“…The traditional method uses a broadband photodetector combined with an optical filter, which is bulky in size and makes the system complex. Narrowband photoresponse can be realized through several strategies such as using narrow absorption active layers, , charge collection narrowing, − self-filtering, electron-donating amine-interlayer-induced doping, and enhanced charge transfer state absorption by optical resonance . An innovative design of a tunable narrowband photoresponse has been realized by the combination of a Fabry–Perot cavity and a broadband organic detector .…”

Advances in Polymethine Dyes for Near‐Infrared Organic Photodiodes†

“…As a result, the OPD with a device structure of ITO/TiO 2 /Jcy/MoO 3 /Ag delivered an EQE at 990 nm of 12% at –2 V (Figure 6d) and a fast responding speed with a f ‐3dB of 50 kHz. [ 73 ]…”

“…Experimental results showed that the OUC device achieved a maximum P2PCE of 0.61% at 10 V under 830 nm NIR light excitation, a high luminance leveled off at 670 cd·m −2 beyond ~6 V and the maximum luminance on/off ratio of 4211 at 5 V. Shortly after, this group further reported two high image‐contrast, narrowband OUCs by combining J‐aggregated Jcy‐based OPD with a fluorescent poly ( para ‐phenylene vinylene) copolymer (Super Yellow, SY)‐based OLED and a host‐guest phosphorescent Ir(ppy) 3 OLED, respectively. [ 73 ] In this type of OUCs, a two‐layer film was inserted as the EBL to suppress the dark current substantially, resulting in high luminance on/off ratios (~10 5 ). Both of OUCs showed high visible transmission of over 85% for the full OUC stacks and small reabsorption of emitted light.…”