Evolution of the high efficiency triple junction solar cell for space power

Emcore is presently qualifying the fourth generation triple junction (3J) solar cell under the Air Force ManTech program. This cell referred to as the ZTJ, is designed to achieve 30% conversion efficiency under 1 sun AM0 illumination. In addition a companion cell with a monolithically integrated protection diode referred to as the ZTJM is under qualification at Emcore with a target AM0 efficiency of 29.5%. We present performance results of each of these 3J cells from pilot line production. In addition, modeling results of various 3J solar cell designs are discussed to motivate the use of a new 3J architecture that relieves the constraint of an active germanium subcell. This new architecture known as inverted metamorphic multi-junction (IMM) allows one to more easily realize the optimum set of band gaps in monolithically connected n-junction solar cell devices. Finally, recent performance results of our fifth generation 3J cell known as the 3J IMM are reported here.