Near-infrared OLEDs pave the way to new markets
The high cost of OLED devices means they are still unaffordable to most, but there is little doubt that their unique characteristics and economies of scale will eventually allow them to reach beyond well-off buyers. In the meantime, researchers funded under the OSNIRO (Organic Semiconductors for NIR Optoelectronics) project have been investigating a specific category of OLEDs emitting in the near infrared (NIR) region (wavelengths longer than 700 nm). Using recent advances in BODIPY – a specific class of boron-containing moieties – synthesis, the team was able to demonstrate OLEDs with emission peaking at 720 nm and external efficiencies up to 1.1 %, one of the highest values reported so far for a NIR-OLED not containing heavy or toxic metals. This means, among other things, that NIR OLED-based bio-sensing applications can now be seriously considered. “Several novel semiconducting materials for NIR electroluminescence have been generated and tested, and the best performing ones are two-component systems with the NIR emitter blended into a semiconducting polymer matrix,” explains Prof. Dr Ullrich Scherf, scientific coordinator of OSNIRO. “Besides, two-component systems for use as NIR photodetectors have been introduced and are based on blends of a NIR absorbing donor component and a fullerene acceptor.” Prof. Dr Scherf qualifies the performances of these NIR electroluminescent and NIR photovoltaic devices as ‘promising’. These include improvements in solar cells with power conversion efficiencies exceeding 11 %, whilst the photodetectors essentially provide increased External quantum efficiency (EQE) and lowered dark currents. One of the photodetectors reaches an EQE of 67 % at an 800 nm wavelength. And this is only a first step in a range of improvements the consortium hopes to achieve. As Prof. Dr Scherf points out, “our devices may be further improved by optimising materials, composition/mixing ratios, electrodes, etc.” Such follow-up research is already ongoing through bilateral cooperation between project partners, including potential users such as Siemens Healthcare and Advent Technologies. A new generation of scientists In addition to research and development, OSNIRO was also focused on skills. Young chemists, physicists, engineers and materials scientists received intense training in the field of optoelectronic devices using organic materials operating in the NIR region. A total of 17 fellows were recruited and given an opportunity to work on their own scientific projects, and this training programme resulted in as many as 29 articles in high-ranked journals. On the device front, project partner SHC has already filed a patent application, and others should follow in the near future. Prof. Dr Scherf is confident that, within three to five years, OSNIRO will enable the commercialisation of products such as night-vision goggles or imaging and sensing devices for biomedical applications.
