New tandem upconversion device improves night vision technology

Researchers have developed a better way of seeing in the dark. In Applied Physics Letters, the research team reports improving on near-infrared upconversion devices, which convert near-infrared radiation to shorter, visible wavelengths. They created a two-stage, tandem device using organic light-emitting diodes (OLEDs). With much higher efficiencies than previous models, the device may offer a promising alternative for low-cost, large-area imaging technologies.

Devices that convert longer wavelength light into visible light have wide use in night vision devices, medical imaging, range finding and even homeland security. Inorganic semiconductors featured in early models have since been replaced with organic alternatives that offer components that are cheaper and easier to fabricate. This new imaging device uses organic materials previously used in solar cells and removes the necessity of read-out electronic components.

Using low-cost semiconductors, the researchers sandwiched a charge-generation layer, which absorbs the incoming near-infrared light, between two organic light-emitting diodes. The double-layer of OLEDs, unlike conventional architectures that typically have only one such layer, helped double the conversion efficiency by capturing both the electron and the hole charge carriers pair-produced by an incident near-infrared photon.

The double-layer structure also proved effective in suppressing leakage current and achieving a higher on/off switching and NIR-to-visible conversion efficiency over traditional upconversion devices. This device absorbed 13 percent of incoming light at 980 nanometers, which it converted to visible green light with an efficiency of 5 percent, near the theoretical limit. The researchers believe the new method can be widely applied in new imaging devices.

Source: “Integrated tandem device with photoactive layer for near-infrared to visible upconversion imaging,” by Shou-Jie He, Deng-Ke Wang, Zhen-Xin Yang, Jia-Xiu Man, and Zheng-Hong Lu, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5023430 .