Publication date: 23rd October 2020
Perovskite solar cells (PSCs) represent one of the most promising and emerging photovoltaic technologies. The strong interest to the PSCs is stemmed from the predicted low cost, simplicity of manufacturing, and high efficiency of perovskite photovoltaics, which currently reaches 25.5% and becomes comparable to the efficiency of the crystalline silicon solar cells [https://www.nrel.gov/pv]. The main obstacle for PSCs commercialization is their insufficient stability under realistic operational conditions.
There is a growing evidence that the efficiency and stability of PSCs can be influenced by the top interfacial charge-transport layer. In particular, in standard n-i-p configuration, the hole-transport layer (HTL) should provide selective and efficient hole extraction, sufficient hole-mobility (µh > 10‑4 cm2 V‑1 s‑1), and good encapsulation properties to ensure the high device performance and long-term operational stability. Application of the state-of-the-art polytriarylamine (PTAA) as HTL materials enables high efficiency and reasonable stability of PSCs [1]. However, the low solubility of PTAA in organic solvents (~6 mg ml-1 in hot chlorobenzene) leads to the appearance voids and inhomogeneous coverage of the perovskite surface [2]. Recently it has been shown that the introduction of the oligomeric ethylene glycol substituents results in increased material solubility and improved HTL adhesion to the perovskite absorber layer [3].
In this work, we present the design, synthesis, and investigation of four novel low molecular weight and polymeric triphenylamine-based compounds bearing oligomeric ethylene glycol substituents. The materials were investigated as HTL materials in PSCs with ITO/SnO2/PCBA/perovskite/HTL/MoOx/Ag configuration (where PCBA is [6,6]-phenyl-C61-butyric acid) [[5]]. It was shown that the application of the low molecular weight compounds as HTL materials leads to an increase in the short current density (Jsc), and a decrease in the open-circuit voltage (Voc) and the fill factors (FF) as compared to the PTAA-based reference devices. In contrast, the application of the polymeric materials with ethylene glycol substituents enabled improved FF and Voc, which indicates reduced defect density at the perovskite/HTL interface.
Thus, we can conclude, that the highly soluble PTAA analogs containing the oligomeric ethylene glycol substituents could be promising HTL materials for high-performance perovskite solar cells.