Solar cells are photovoltaic devices, while LEDs and organic light-emitting diodes (OLEDs) are light-emitting devices. Both share a common diode structure based on identical underlying energy configurations. Developing a single device that combines both photovoltaic and light-emitting functions would make it possible to charge a smartphone display simply by exposing it to sunlight. However, devices that successfully reconcile high power generation efficiency with high light emission efficiency have achieved very little success until now.
A research team including Associate Professor Seiichiro Izawa at the Institute of Integrated Research, Institute of Science Tokyo, has successfully developed an organic solar cell that possesses both high-efficiency photovoltaic functionality and light-emitting functionality within a single device. Generally, the light emission efficiency of organic solar cells remains extremely low, at 0.1% or less. When high-energy state molecules transition to a lower-energy state, they settle into a configuration that suppresses light emission. To overcome this bottleneck, the research group combined two types of luminescent molecules typically utilized in the OLED field, successfully engineering an energy structure that inhibits the transition into these non-emissive states. Furthermore, when they fabricated a diode device using these molecules and exposed it to simulated sunlight, the device generated a high voltage of 1.83 V, which is close to the theoretical limit, and achieved a photoelectric conversion efficiency of over 1%. Conversely, when voltage was applied to the same device without light irradiation, it emitted red light at a wavelength near 620 nm (nanometers, where nano represents one-billionth), demonstrating a light emission efficiency exceeding 1%.
This result opens the door to integrating power generation capabilities into OLED displays. It is also expected to lead to a wide range of applications, including further improving the conversion efficiency of organic solar cell devices.
(Article: Masanori Nakajo)
(Bottom) The stored electricity is then used to cause the exact same device to emit light.