Four-junction solar cells for space and terrestrial applications require a junction with a band gap of for optimal performance. InGaAsN or InGaAsN(Sb) dilute nitride junctions have been demonstrated for this purpose, but in achieving the short-circuit current needed to match typical GaInP and GaAs junctions, the open-circuit voltage () and fill factor of these junctions are compromised. In multijunction devices incorporating materials with short diffusion lengths, we study the use of thin junctions to minimize sensitivity to varying material quality and ensure adequate transmission into lower junctions. An device with absorber thickness has sufficient short-circuit current, however, it relies less heavily on field-aided collection than a device with a absorber. Our standard cell fabrication process, which includes a rapid thermal anneal of the contacts, yields a significant improvement in diffusion length and device performance. By optimizing a four-junction cell around a smaller 1-sun short-circuit current of , we produced an InGaAsN(Sb) junction with open-circuit voltage of 0.44 V at 1000 suns (), diode ideality factor of 1.4, and sufficient light transmission to allow in all four subcells.