The metallization of silicon heterojunction (SHJ) solar cells by electroplating of highly conductive copper onto a multifunctional patterned metal layer stack is demonstrated. The approach features several advantages: low temperature processing, high metal conductivity of plated copper, no organic making, and low material costs (almost Ag‐free). A PVD layer stack of copper and aluminum is deposited onto the cell subsequently to TCO deposition. The aluminum layer is patterned with a printed etchant and its native oxide on the remaining areas inhibits plating. The full area aluminum layer while electroplating supports plating current distribution and allows homogeneous plating height distributions over the cell. The NOBLE (native oxide barrier layer for selective electroplating) approach allows reaching a first encouraging SHJ solar cell efficiency of 20.2% with low contact resistivity.
Silicon diode arrays for use as the electron‐beam accessed target in camera tubes for the Picturephone® visual telephone set have been fabricated and their properties evaluated. These targets offer significant advantages over the antimony trisulfide target commonly used in vidicon‐type tubes. But there are certain potential limitations which must be dealt with in developing a silicon target. Three of its critical requirements are adequate sensitivity to visible light, low dark current, and junction uniformity and freedom from defects across at least 300,000 diodes per square centimeter. Sensitivity to visible light is expressed here by the efficiency for conversion of incident photons to electrons in the read‐out circuit. Conversion efficiencies exceeding 50 percent in the visible region have been achieved by oxidizing or by diffusing phosphorus into the light‐receiving surface to reduce the surface‐recombination velocity. Diode leakage currents of ≦1 × 10−13 A per diode are required, and are obtained for target voltages up to about 5 to 7 V. Surface generated current dominates in the 8μ diameter diodes of the array, but this component of current can be reduced substantially by use of (100) surfaces or by hydrogen annealing. Visible defects in a picture can result from leaky diodes or oxide pinholes which cause bright spots, and diodes covered by oxide which cause dark spots. Our best targets show a video display with only a few defects; processing must be improved to eliminate delects comvletelv.
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