We report on the development ofp‐on‐nGaxIn(1−x)As thermophotovoltaic devices. For Ga0.47In0.53As cells, lattice‐matched to InP and having a bandgap of 0.73 eV, then‐on‐pconfiguration gives better results than thep‐on‐nconfiguration. However, for Ga0.32In0.68As cells, grown on InP and having a bandgap of 0.58 eV, thep‐on‐npolarity has superior performance for cells with similar step‐graded buffer layers. The improvement in thep‐on‐ndevices is due to reduced dark currents and increased open circuit voltages (Voc). Optimized back surface field layers produce these effects. Because of the absorption of long wavelength light in the base region of low bandgap materials, a high quality back surface acts as a minority carrier mirror and reduces recombination in buffer layers. We have been able, so far, to get more effective back surface field layers with thep‐on‐nconfiguration. While then‐on‐ppolarity may offer the advantage of lower cell emitter sheet resistivity, thep‐on‐ndevice offers lower free carrier absorption of long wavelength radiation, better spectral control of incoming radiation, and improved large scale manufacturing ability. Results for several differentp‐on‐ncell structures for the 0.73 eV and 0.58 eV GaxIn(1−x)As compositions will be reported. ©1996 American Institute of Physics.