Background
Wide-bandgap perovskites are indispensable materials for achieving high efficiencies as top sub-cells in perovskite-silicon tandem and all-perovskite tandem solar cells. However, WBG perovskites, particularly in mixed bromine-iodine systems, have faced persistent challenges regarding instability, such as phase segregation and defect formation. Overcoming these issues requires a deep understanding of defect characteristics and effective control techniques. This research not only deepens the fundamental physicochemical understanding of perovskite materials but also provides concrete material design strategies to improve their stability, thus significantly contributing to the practical implementation of next-generation high-efficiency solar cells.
Key Findings
New research has unveiled that defect properties in mixed-halide perovskites exhibit bandgap-dependent behavior, leading to a crucial advancement in materials science understanding. Specifically, in bromine (Br)-rich wide-bandgap (WBG) perovskites, defect activation energy was found to increase with increasing bandgap, resulting in the formation of deeper defect states. One of the primary factors hindering the efficiency and stability of perovskite solar cells is the presence of these defects within the crystal and at interfaces. These defects promote “non-radiative recombination,” where light-generated electrons and holes are lost before they can be converted into electrical power. This study revealed that in perovskites with high bromine concentrations, as the bandgap widens, defect energy levels become deeper, which facilitates charge carrier trapping and degrades device performance.
Based on this insight, a novel passivation technique using p-phenylenediamine diiodide for iodide-vacancy-related defects was developed. The introduction of p-phenylenediamine diiodide successfully “passivated” (inactivated) defects associated with iodide vacancies (missing iodine atoms) within the perovskite crystal. This passivation layer neutralizes defect states, improving charge carrier transport efficiency and significantly suppressing non-radiative recombination. As a result, carrier lifetimes were extended, leading to improved open-circuit voltage (Voc) and fill factor (FF) of the solar cell, and ultimately, enhanced overall conversion efficiency and device performance.
Strategic Significance & Outlook
These new insights into defect control will profoundly impact the design and optimization of mixed-halide perovskite solar cells. Specifically, by improving the stability and efficiency of WBG perovskites, it will be possible to further enhance the overall performance of tandem solar cells. Moving forward, research will focus on integrating this passivation technique into large-scale manufacturing processes and verifying its applicability to different perovskite compositions. This is expected to accelerate the commercialization of more durable and highly efficient perovskite solar cells, thereby improving the cost-effectiveness and adoption rate of solar power.
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