Exfoliated sub-10μm thin germanium for cost-effective germanium based photovoltaic applications

Germanium based photovoltaic cells have found applications in both space/satellite and terrestrial systems such as high-efficiency multi-junction concentrator solar cells. In these applications, the main emphasis is on increasing the cell efficiency, as opposed to cost reduction. Recently, there has been more widespread application of Ge in other areas such as low light conditions and thermophotovoltaic (TPV) systems where cost-effectiveness is important. In order for this to be commercially viable, a low-cost solution for developing Ge cells would be essential. To this end, our approach is to minimize the amount of Ge material used. In this paper, we demonstrate for the first time a novel exfoliation technology capable of producing sub-10μm thin flexible Ge foils for cost-effective Ge based photovoltaic applications. First, computer simulation was used to study the influence of substrate thickness on the open circuit voltage and efficiency of Ge single-homojunction cells. Then, our novel exfoliation technology was applied to Ge cells to realize thin flexible foils. Our preliminary experimental results show an increase in open-circuit voltage from 150 mV (non-exfoliated cell) to 270 mV (exfoliated cell), in agreement with our simulation results.