Photoluminescent and electroluminescent couplings in monolithic tandem solar cells

As solar cell efficiency improves, so does the cell's radiative efficiency. In high-performance tandem stacks, each individual cell emits significant luminescence during operation, making radiative coupling between these cells an important factor to consider in cell design, measurement and performance prediction. Past modelling includes the electroluminescent coupling component only, although photoluminescent coupling is likely to be important for cells operating near or below their maximum power point voltage or when junction defect recombination is dominant. In this work, we first propose an extension of earlier models to allow this non-negligible coupling component to be included, which is validated by measurement of the closely related external emission. Then, we establish an equivalent circuit and uniquely use intuitive circuit concepts to conduct a comprehensive analysis clarifying the roles of parasitic circuit elements and external loads in the complex radiative interactions between cells. The circuit analysis also reveals some undiscovered issues to be addressed in eliminating coupling effects from measured cell spectral responses. Copyright (c) 2016 John Wiley & Sons, Ltd.