A payback assessment for materials development for the low-gap unit of a multi-junction cell: a numerical modeling study

The objective of this paper is to demonstrate how computer simulations can be used to determine the best payback when the improvement of solar cell efficiency is sought. For this demonstration, modeling work has been undertaken to examine how the material quality of the absorber and p/i interface layers of the a-SiGe:H heterojunction of a triple junction can affect device performance. According to simulation results, which are based on assuming a simplified a-SiGe:H sub-cell structure with only doped layers, interfacial layers, and a homogeneous absorber, the authors find that the scheme with the best payback for enhancing cell efficiency is different for the absorber layer and the p/i interface layer. For the absorber, the density of mid-gap states is the most important factor, but for the p/i interface layer the mobility gap is the most dominant factor. Their numerical analysis approach allows the determination of where material improvement efforts will have the most effect. Put succinctly, the relative importance analysis, which can be achieved with simulation, shows where material development efforts will have their best payoff chances