The bandgap of InP is near ideal for the high theoretical conversion efficiency of the air mass zero (AM0) light spectrum experienced in space. This combined with the well known radiation resistance makes InP an ideal candidate for space solar cell use. The p/n configuration has several advantages over the n/p configuration, however, the conversion efficiency of p/n InP cells has been low compared to the n/p configuration, mostly do to poor performance of the Zn doped emitter. We have recently achieved a 17.6% AMO conversion efficiency for a p/n InP cell on an InP substrate and have achieved this record efficiency through understanding of the role of Zn interstitial defects and the hydrogen interactions with these defects. The effect of the Zn defect on device performance will be described.