Understanding the Role of the Subcells in Two Terminal All-Perovskite Tandem Solar Cells Using Absolute Hyperspectral Imaging in Electroluminescence Mode

In all-perovskite tandem solar cell structures, multiple perovskite absorber layers with narrow and wide band gaps are used to maximize sunlight energy conversion. Tin and lead halide perovskites, having narrow and wide band gaps, respectively, are key components for achieving high efficiencies in tandem perovskite solar cells. Perovskites have great potential to reach the theoretical power conversion efficiency of around 33% in single-junction solar cells and around 40% in all-perovskite tandem solar cells [1]. A comprehensive understanding of the physics of charge carrier generation and recombination in perovskite tandem solar cells is very important for optimizing layer configurations to achieve maximum light absorption and conversion efficiency.
In this work, we performed electroluminescence (EL) imaging experiments on low and wide band gap perovskite single junction solar cells, as well as all-perovskite tandem solar cells. The EL external radiative efficiency (ERE), calculated as the ratio of the total external radiative emission current (qR^t_e^o_x^t_t) to the total dark recombination current density (J_dark), was plotted as a function of the junction voltage (V) at various current densities (J). Separately, extensive dark and light J-V measurements were performed on the same devices. To analyze and interpret the measurements, we applied a 2-diode recombination current model, composed of both radiative and nonradiative components, to both the ERE-J and the J-V curves simultaneously and systematically investigated the differences between single junctions or subcells within tandem structures. We show that individual subcell J-V curves in a two-terminal tandem configuration can be accurately predicted from just the ERE measurements combined with a single dark or light J-V measurement. Therefore, we gain an understanding of what each subcell’s contribution is to the overall performance of the tandem structure and how the nonradiative losses in each subcell hamper the power conversion efficiency of the entire cell. These results have implications for advancing next-generation high-efficiency and cost-effective photovoltaics.

[1] Wu, S., Liu, M. and Jen, A.K.Y., 2023. Prospects and challenges for perovskite-organic tandem solar cells. Joule, 7, 484-502.