On the performance and reliability of state-of-the-art commercial UV-C LEDs for disinfection purposes

Abstract

In the last year the market of ultraviolet (UV) light-emitting diodes (LEDs) had a huge increase due to the higher demand of devices caused by the pandemic crisis. In fact, it was demonstrated that UV LEDs, and in particular UV-B and UV-C LEDs, could be used as efficient sources for the disinfection of surfaces against Sars-CoV-2. In this work, we investigated electrical, optical and spectral degradation mechanisms in a series of commercial UV-C LEDs (275 nm – 280 nm) available on market. We present an exhaustive comparison of the main sample characteristics, studying their evolution when the LEDs are submitted to constant current stress tests (for about 350 h) at the absolute maximum current indicated in the respective datasheets. In particular, we carried out an extensive set of measurements, including current-voltage (I-V), optical power-current (L-I) and power spectral density (PSD) characteristics at various steps of stress, combined with the analysis of the drive voltage during the tests and of the thermal droop of the devices. We found: (i) a set of LEDs with a promising L80 of 10000 min (about 170 h), (ii) the presence of parasitic peaks and bands in all devices, ascribed to radiative recombination outside the QWs, and (iii) a substantial increase in thermal droop in all LEDs due to a decrease in injection efficiency and an increase in SRH recombination events during the stress tests.