Cell phone users worry constantly about dwindling battery charge. To eliminate that concern, AstroPower Inc., of Newark, Del., is trying to build a small array of crystalline silicon solar cells linked like circuit elements on a microchip. This "monolithic" connection permits a large number of cells to be hooked up in series-stepping up the voltage to the required level without introducing the electrical resistance that ordinary wiring would produce.

Unlike the amorphous silicon used in calculators, the crystalline devices require sunlight-not indoor fluorescent illumination-to generate electricity. Still, says AstroPower's Lou Dinetta, a roughly 2.5-by-5-centimeter array would supply enough power for an hour of talk time. Wearing the cell phone on the hip outdoors would expose it to enough sunlight to maintain the phone in stand-by mode indefinitely. AstroPower is negotiating with at least one major cell-phone maker.