Minimizing Open-Circuit Voltage Losses in Perovskite/Perovskite/Silicon Triple-Junction Solar Cell with Optimized Top Cell

Following the impressive efficiencies achieved for two-terminal perovskite/silicon dual-junction solar cells, perovskite/perovskite/silicon triple-junction cells have now gained attention and are rapidly developing. In a two-terminal triple-junction cell, maximizing the open-circuit voltage (VOC) is not straightforward as it requires understanding and mitigating the dominant losses in such a complex structure. Herein, the high bandgap perovskite top cell is first identified as the main source of the VOC loss in the triple-junction cell. A multifaceted optimization approach is then implemented that improves the VOC of the 1.83 eV perovskite. This approach consists of 1) replacing the reference triple-cation/double-halide with a triple-cation/triple-halide perovskite, which improves perovskite bulk quality and reduces transport losses, and 2) implementing a piperazinium iodide passivation between the perovskite and the electron transport layer, which reduces nonradiative recombination losses at this interface. Employing these optimizations in the top cell of the triple-junction boost the VOC by average 124 mV. A high VOC of more than 3.00 V is achieved with a fill factor of 79.6%, a short-circuit current density of 9.0 mA cm-2, and an efficiency of 21.5%. Further study is conducted on the improvement of VOC in the triple-junction solar cell using subcell selective photoluminescence-based implied VOC imaging, which is applied for the first time to a perovskite-based triple-junction structure.