Investigating Hole Extraction and Stability in Triple Cation Wide Bandgap Perovskite Solar Cells

Triple-cation (TC) perovskite solar cells (PSCs) with the general formula APbX₃, where the A-site cations are a combination of formamidinium (FA⁺), methylammonium (MA⁺), and cesium (Cs⁺), have demonstrated optimal power conversion efficiencies and long-term stability. Additionally, the bandgap of these perovskites can be effectively tuned by adjusting the stoichiometric ratios of halides (X = I, Br, and Cl), enabling the development of wider bandgap materials suitable for tandem and multi-junction solar cell applications. Therefore, further advancements in device architecture and a deeper understanding of fundamental charge transport mechanisms are imperative to enhance the performance of these devices.
Charge transport layers play a critical role in determining the performance and stability of perovskite solar cells. Specifically, efficient hole extraction through the hole transport layer (HTL) has been reported as a dominant factor influencing the efficiency and reliability of single-cation CH₃NH₃PbI₃ PSCs. However, the extent of this influence in triple-cation PSCs remains inadequately explored.
This work investigates the role of the HTL in TCPSCs with a p-i-n device structure. A triple-cation mixed-halide wide-bandgap perovskite with a bandgap of approximately 1.8 eV is developed and studied to assess the impact of HTL modifications, including (i) the insertion of an interface layer based on copper halide (CuX) and (ii) the use of a p-type dopant. Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) serves as the reference HTL. Various combinations of films and complete devices are examined for their efficiency and long-term stability under illumination. The strategies adopted in this study are expected to enhance both the efficiency and stability of wide-bandgap TCPSCs by enabling more efficient hole extraction and reducing phase segregation of halide phases.