Inverted p/n InGaAs-based thermophotovoltaic converters via control of Zn out-diffusion from InP layers

Although inverted n/p InGaAs cells have achieved record performance for thermophotovoltaic (TPV) applications, inverted p/n cells are also of interest for building high-density TPV modules and are required in thermophotovoltaic-thermionic (TIPV) systems to enable electron injection from the emitting cathode into the valence band of the TPV subcell. However, in these p/n cells, Zn out-diffusion from buried InP layers into the absorber structure severely degrades the electrical performance of the device. In this work, we describe our efforts to control the resulting Zn doping profile by strategically designing the Zn incorporation during the epitaxial growth of the structure. Electrical performance comparable to that of the reference inverted n/p cell at low current densities was achieved. However, even with our best results, performance at high irradiance levels remains limited. Simulations attribute this limitation to potential barriers in the valence band, which restrict the performance of these inverted p/n cells even in the absence of Zn diffusion, highlighting an intrinsic challenge in matching the performance of inverted n/p cell. • Strong Zn out-diffusion from InP layers is observed in inverted p/n InGaAs photovoltaic cells. • Depletion of Zn in InP layer produces valence band potential barriers for carrier transport and a drastic fill factor drop. • Diffusion of Zn into InGaAs absorber layers lowers the V OC . • Zn precursor flow modulation during epitaxy improves doping profiles and boosts performance despite inevitable diffusion. • Zn diffusion challenges the development of more complex structures comprising Zn-doped InP layers grown early in the structure.