Can Self-powering Displays Become Reality?

In recent years, researchers have been exploring multifunctional devices that can both generate and emit light. Although several prototypes based on inorganic materials have been reported, most operate only with near-infrared light, which is invisible to the human eye and therefore unsuitable for displays. Some also rely on heavy metals, raising environmental concerns.

Organic semiconductors are considered a promising alternative. Made from carbon-based molecules, they are lightweight and flexible, making them well suited for bendable displays and wearable electronics.

However, organic semiconductors also face a major challenge. Some of the energy that should be used for generating electricity or producing light is instead lost as heat. As a result, devices that are good at generating electricity usually emit light poorly, while devices that emit light efficiently often generate electricity less effectively. Achieving both functions in a single device has therefore remained difficult.

To overcome this challenge, a research team led by Associate Professor Seiichiro Izawa at Institute of Science Tokyo (Science Tokyo) designed a new molecular structure for organic semiconductor materials. Their device successfully combines three functions-power generation, light emission, and light detection-within a single organic semiconductor junction.

The biggest obstacle to combining power generation and light emission has been energy loss as heat.

The researchers focused on a special type of material whose molecular shape changes very little as electrons move through it. In conventional organic semiconductors, moving electrons cause molecules to vibrate, and part of the energy is released as heat. By using materials with more stable molecular structures, the team dramatically reduced this unwanted energy loss.

The improvement was remarkable. The rate of heat loss was reduced to less than one hundred-thousandth of that in conventional organic solar cells.

As a result, the new device achieved high performance in both electricity generation and light emission. Previous devices were typically optimized for one function or the other, but not both. This study demonstrates that both can be achieved simultaneously in a single device.

Another important achievement is that the device performs efficiently in visible light. Most previous multifunctional devices operated only in the near-infrared region, making them unsuitable for display applications. In contrast, the new device emits bright red light that is suitable for displays with brightness comparable to that of smartphone screens.

Previous studies had demonstrated devices that excelled either at power generation or at light emission. However, this is the first demonstration of a single junction that integrates power generation, light emission, and light detection. This achievement could change the conventional approach of using separate components to harvest light and display images.

This research opens the door to a new generation of displays that not only consume electricity but also harvest light to generate their own energy.

In the future, such technology could lead to self-powered displays that harvest light during the day and function as displays when needed. Because organic semiconductors are lightweight and flexible, they could also be used in wearable electronics, skin-mounted health sensors, and smart windows that combine power generation with lighting.

In addition, the device functions as a light sensor. By integrating light harvesting, light emission, and light detection into a single component, this technology could fundamentally change the way future electronic devices are designed.

This study began with a fundamental question: how can we design molecules that minimize energy loss as heat inside solar cells? One of the most fascinating aspects of organic semiconductor research is that the molecular design has a direct impact on the performance of optical devices.

In the future, displays may do much more than simply show images. They could harvest light, emit light when needed, and even sense the light around them.

(Seiichiro Izawa, Associate Professor, Materials and Structures Laboratory, Institute of Science Tokyo)

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