Screen printed metal matrix composite contacts for crack tolerant solar cells

Abstract

Solar cells used in space missions are the primary source for power on board the space vehicle. Space solar cells are becoming thinner for improved performance (W/kg) and are based on single crystalline materials where fracturing or cleaving can easily occur from packaging, deployment and constant temperature cycling in outer space. When the fracture in the semiconductor extends through the solar cell metallization, loss of power will occur and can hinder a mission. A novel semiconductor metallization is being developed that may enable the solar cells to be fully crack tolerant. The material consists of carbon nanotubes impregnated silver metallization, termed metal matrix composite, deposited by screen printing. The carbon nanotubes increase the fracture toughness of the metallization and also offers a redundant electrical path should the metal matrix fracture. In addition to these benefits, the use of screen printing will facilitate lower costs and ease of manufacturability by eliminating the expensive photolithography and evaporation steps used for conventional metallization. The inks that are being developed show promise of electrically bridging cracks and are further being tuned for screen printing processes.