From light emission to solar power: Experiment on LED's photovoltaic behavior

An experimental study to investigate the fundamental similarities between light-emitting diodes (LEDs) and solar cells (SCs) for educational purposes is here presented. Through a hands-on experiment using inexpensive, commercially available LEDs and simple laboratory equipment, students are introduced to characterization techniques, such as electroluminescence (EL) and current–voltage (I–V) measurements, as well as to optoelectronic devices, photovoltaic physics, spectroscopy, light-to-matter interactions, and solid-state physics concepts. Four LEDs of different colors—red, amber, green, and blue—are used in this study. The measured EL spectra allowed an estimation of the bandgap energy of the material constituting each LED's optical active layer, establishing a relationship with the LED color. Photovoltaic mode I–V curves are measured under outdoor sunlight, demonstrating that all LEDs exhibited photovoltaic behavior, generating electrical energy from incident light. The red LED produces sufficient electrical energy to power a small calculator, while the green LED exhibited the poorest photovoltaic performance. Shockley–Queisser (SQ) theory is employed to comparatively investigate the “photovoltaic” quantum efficiency (QE) of the LEDs, enabling students to relate the results to the well-known green gap problem in LED “emission” QE. This work effectively illustrates the similarities between LEDs and SCs, bridging the gap between theoretical knowledge and practical application, providing students with a valuable learning experience in solid-state physics, semiconductor-related topics, and photovoltaic technology.