TECHNOLOGY
Engineer D. Ε. Thomas of Bell Telephone Laboratories demonstrates that his voice can be clearly heard by M. B. Prince at a receiver of a small mobile radio transmitter across the lawn of the Murray Hill, N. J. laboratory facilities where the solar device was invented. Inset shows Bell solar battery unit which has been used experimentally to power a transistor radio transmitter. Bell envisions use of the battery in telephony, in such equipment as mobile radio-telephone systems and as sun-powered battery-chargers for rural telephone systems, such as tHat now under trial at Americus, Ga.
Electricity from Sunlight Silicon battery converts sun's energy directly into electrical energy; transformation of 6 % is feasible A NEW solar battery, able to transform 6% of total incident light en ergy into electrical energy was un veiled last week by Bell Telephone Laboratories. Previously available photoelectric devices have never been rated higher than 1%. Bell Laboratories scientists expect that, by further improvements in de sign, efficiencies of up to 10% may be realized. The maximum possible effi ciency is about 22%, owing partly to the fact that only a portion of the light spectrum is effective in activating the device. The solar battery consists of waferthin silicon strips, each measuring about 0.5 by 2 inches. To one surface of the high-purity silicon has been added a layer of boron to a depth of less than 0.0001 inch. The boron has been introduced by treating the silicon at high temperatures with a boron-con taining gas. The solar device makes use of P-N (Positive-negative) junctions, which are the bases of the junction transistor, 1768
The P-N junctions consist of semi conductors containing small, controlled amounts of impurities, such as boron or arsenic. Battery is cast in Plexiglas or lucite. In the solar device, the incident light causes the displacement of elec tions in the semicon ductor. This electron movement produces the observed electrical cur rent.
The light-sensitive strips, linked to gether electrically, can deliver power at a rate of 50 watts per square yard of surface. The voltage generated per strip is about 0.5 volt, while the current output is about 24 ma. per square centimeter. Because of the internal impedance of the silicon, higher efficiencies are ob tained when a series of strips are used rather than a single large surface. The solar battery should theoreti cally last indefinitely since there are no moving parts and nothing is consumed or destroyed in the energy conversion process. The device might effectively be used to power the transmission of voices over telephone wires. It has al ready been used experimentally to power a radio transmitter carrying both speech and music. In the design of the solar devices, about three to five times as much sur face must be used than would be re quired for daylight operation only. The excess electrical energy developed dur ing the daytime can be stored in auxil iary storage batteries so that sufficient power is also available at night and on sunless days. Among the other silicon devices be ing investigated ai Bell Laboratories is a lightning protector for telepone lines which would be more compact and easier to maintain than those now available. Also under study is a power rectifier that can convert large amounts of alternating current into direct cur rent. An important feature of these devices is that they can operate at much higher temperatures than other crystal rectifiers.
Inventors of the battery, left to right: G. L. Pearson, D. M. Chapin, and C. S. Fuller. They are checking sample devices for the amount of elec tricity derived from sun light, here simulated by a lamp C H E M I C A L
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