selenium cell

selenium cell
Name	Selenium cell
Caption	Photovoltaic selenium cell used historically for photography and television
Invented	Late 19th century
Inventors	Willoughby Smith; George Eastman (developer)
Application	Photodetection, photography, television signal detection, power generation (historical)
Material	Selenium

selenium cell

A selenium cell is a photoelectric device that converts light into electrical signals or current using the photoconductive and photovoltaic properties of selenium. Early selenium cells played a central role in the development of photography, early television receivers, and industrial light meters, linking breakthroughs by inventors and firms such as Willoughby Smith, Guglielmo Marconi, Thomas Edison, and George Eastman. Though largely superseded by modern semiconductors like silicon photodiodes and gallium arsenide detectors, selenium cells remain of historical and pedagogical interest in the histories of electrical engineering and optics.

Introduction

Selenium cells exploit the element selenium's ability to change electrical resistance or generate electromotive force when illuminated. Discoveries by Willoughby Smith in the 1870s and later commercialization by companies such as Eastman Kodak Company and manufacturers in Germany and United Kingdom connected selenium devices to enterprises like RCA and scientific institutions including Bell Labs and Royal Society. They were integral to technologies demonstrated at expositions like the Great Exhibition and incorporated into early experimental systems by figures such as Alexander Graham Bell and Heinrich Hertz.

Design and Operation

A typical selenium cell comprises a layer or layers of crystalline or amorphous selenium deposited on a conductive backing such as copper or aluminum and paired with metal contacts and encapsulation. Illumination alters selenium's charge carrier density, affecting resistivity; in photovoltaic arrangements the junction between selenium and the metal backing yields a photovoltage. Practical construction involved techniques derived from industrial chemistry practiced by firms like DuPont and laboratories associated with Imperial College London and MIT. Operation depends on parameters measured against standards from organizations such as IEEE and National Institute of Standards and Technology.

Types and Variants

Manufactured variants included photoconductive cells for light meter circuits, photovoltaic cells for direct current generation, and compound stacks used in early television camera tubes and scanning apparatus pioneered by inventors like John Logie Baird and Philo Farnsworth. Forms ranged from simple wafer cells used by Kodak in exposure meters to mosaic arrays in experimental imaging devices displayed at institutions such as the Smithsonian Institution and the Science Museum, London. Specialized versions were tailored by laboratories in Prussia and companies like Siemens for industrial control systems.

Performance Characteristics

Key metrics included spectral response, dark resistance, photovoltage, and response time. Selenium exhibits peak sensitivity in the visible to near-infrared bands, with performance influenced by impurity levels and crystalline structure—factors investigated in academic papers associated with University of Cambridge, Harvard University, and ETH Zurich. Compared with later silicon devices, selenium cells typically had higher dark resistance, lower quantum efficiency, and slower temporal response, which limited use in high-frequency communications pioneered by organizations such as AT&T and BBC.

Applications

Historically, selenium cells were used in exposure meters for cameras sold by Eastman Kodak Company, photocells in early broadcasting equipment at BBC studios, light-sensitive controls in industrial plants operated by conglomerates like General Electric, and in experimental phototelegraphy and facsimile systems developed by inventors linked to Western Union and ITT Corporation. They also powered demonstration arrays for public exhibitions sponsored by governments of France and United States and were components in early research at institutions such as Caltech and Max Planck Institute.

Safety and Handling

Selenium is a chemical element handled under controls similar to those used for inorganic semimetals in laboratories compliant with Occupational Safety and Health Administration and European Chemicals Agency guidance. Intact selenium cells pose minimal risk, but powdered selenium, heated selenium, or waste from manufacturing requires careful management, with protocols observed by corporations like BASF and testing in accredited facilities such as those certified by Underwriters Laboratories. Disposal practices align with national regulations administered by agencies like the Environmental Protection Agency.

History and Development

The photoconductive behavior of selenium was first noted by Willoughby Smith in telegraphy research; subsequent commercialization involved innovators such as George Eastman for photographic instrumentation and experimenters in early television like John Logie Baird and Philo Farnsworth. Development trajectories intersected with major industrial families and firms including RCA, Siemens, and General Electric, and were documented in technical journals associated with Royal Institution and academic conferences at Institute of Electrical and Electronics Engineers (IEEE). The eventual decline of selenium cells coincided with the rise of silicon-based semiconductors developed at centers such as Bell Labs and Fairchild Semiconductor, culminating in modern optoelectronic industries concentrated in regions like Silicon Valley and nations including Japan.

Category:Photodetectors