Thermophotovoltaic (TPV) generators can reduce pollution by lowering their operating temperature, but the choice of semiconductor materials for this purpose is limited. We present results on an InGaAs p‐n cell lattice‐matched to InP which is optimised for the Erbia emission spectrum peak at a wavelength of 1.5&mgr;m. However, for lower temperature TPV applications at longer wavelengths one is constrained by the lack of lattice‐matched materials. In order to extend the absorption towards 1900 nm for a selective emitter based on Thulium strain‐compensated InGaAs/InGaAs quantum well cells (QWCs) on InP have been designed and characterised. We present data showing that strain‐compensated QWCs extend the spectral response (SR) to longer wavelengths and can show a lower dark current density than the bulk InGaAs p‐n cell despite the QWC having a lower band‐gap. We have developed a model for the SR of strained multi‐quantum well (MQW) systems in InGaAsP, including quantum effects as well as strain‐induced changes. SR modelling of strain‐compensated structures is compared with experimental data, and efficiencies, for a Thulia spectrum, are predicted. Our study also shows that back surface reflection must be taken into account in these devices. © 2003 American Institute of Physics