A device that detects or measures electromagnetic radiation by generating a current or a voltage, or both, upon absorption of radiant energy. Specially designed photovoltaic cells are used for power generation, as in solar batteries or solar cells, and for sensitive detection of electromagnetic radiation in radiometry, optical communications, spectroscopy, and other applications. An important advantage of the photovoltaic cell in these particular applications is that no separate bias supply is needed—the device generates a signal (voltage or current) simply by the absorption of radiation.