Enabling Durable Bottom Cell for Multi-Junction Thin-Film Photovoltaics

"ITN Energy Systems, Inc. (ITN) intends to meet the requirements for future spacecraft power by developing >20% efficient photovoltaic (PV) cells on lightweight flexible substrates. ITN will achieve this goal using a two-terminal monolithic tandem(multi-junction) structure with thin-films of high-efficiency and radiation resistant copper indium diSelenide (CIS) and bandgap tunable CIS-alloys with Ga and/or Al. As an intermediate goal to this large endeavor, ITN will perform research anddevelopment on a durable bottom cell (low-bandgap) for the multi-junction device, which would survive the harsh processing conditions of the monolithically deposited top cell. This new photovoltaic device will avoid the CdS top heterojunction layer thatis typically associated with CIS-alloy devices, but that is responsible for degradation under top cell processing conditions. Several different pathways to achieving durable bottom cells will be investigated. The achievement of a 10% efficient durablebottom cell would be enabling for the multi-junction device and allow for several promising thin-film technologies as the wide-bandgap top cell. Light weight, flexible, high efficiency, long life, radiation resistant, durable thin film PV modules wouldquickly takeover the small and medium spacecraft power market due to their inherent low cost and high specific power (W/kg). Light weight, flexible, high efficiency, long life, radiation resistant, durable th